Adding upstream version 1:10.11.6.upstream/1%10.11.6upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2845 insertions, 0 deletions

diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
new file mode 100644
index 00000000..210f229a
--- /dev/null
+++ b/sql/sql_explain.cc
@@ -0,0 +1,2845 @@
+/*
+   Copyright (c) 2013 Monty Program Ab
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
+
+#ifdef USE_PRAGMA_IMPLEMENTATION
+#pragma implementation				// gcc: Class implementation
+#endif
+
+#include "mariadb.h"
+#include "sql_priv.h"
+#include "sql_select.h"
+#include "my_json_writer.h"
+#include "opt_range.h"
+#include "sql_expression_cache.h"
+
+#include <stack>
+
+const char * STR_DELETING_ALL_ROWS= "Deleting all rows";
+const char * STR_IMPOSSIBLE_WHERE= "Impossible WHERE";
+const char * STR_NO_ROWS_AFTER_PRUNING= "No matching rows after partition pruning";
+
+const char *unit_operation_text[4]=
+{
+   "UNIT RESULT","UNION RESULT","INTERSECT RESULT","EXCEPT RESULT"
+};
+
+const char *pushed_derived_text= "PUSHED DERIVED";
+const char *pushed_select_text= "PUSHED SELECT";
+
+static void write_item(Json_writer *writer, Item *item);
+static void append_item_to_str(String *out, Item *item);
+
+Explain_query::Explain_query(THD *thd_arg, MEM_ROOT *root) : 
+  mem_root(root), upd_del_plan(nullptr),  insert_plan(nullptr),
+  unions(root), selects(root), stmt_thd(thd_arg), apc_enabled(false),
+  operations(0)
+{
+  optimization_time_tracker.start_tracking(stmt_thd);
+}
+
+static void print_json_array(Json_writer *writer,
+                             const char *title, String_list &list)
+{
+  List_iterator_fast<char> it(list);
+  const char *name;
+  writer->add_member(title).start_array();
+  while ((name= it++))
+    writer->add_str(name);
+  writer->end_array();
+}
+
+
+
+Explain_query::~Explain_query()
+{
+  if (apc_enabled)
+    stmt_thd->apc_target.disable();
+
+  delete upd_del_plan;
+  delete insert_plan;
+  uint i;
+  for (i= 0 ; i < unions.elements(); i++)
+    delete unions.at(i);
+  for (i= 0 ; i < selects.elements(); i++)
+    delete selects.at(i);
+}
+
+
+Explain_node *Explain_query::get_node(uint select_id)
+{
+  Explain_union *u;
+  if ((u= get_union(select_id)))
+    return u;
+  else
+    return get_select(select_id);
+}
+
+Explain_union *Explain_query::get_union(uint select_id)
+{
+  return (unions.elements() > select_id) ? unions.at(select_id) : NULL;
+}
+
+Explain_select *Explain_query::get_select(uint select_id)
+{
+  return (selects.elements() > select_id) ? selects.at(select_id) : NULL;
+}
+
+
+void Explain_query::add_node(Explain_node *node)
+{
+  uint select_id;
+  operations++;
+  if (node->get_type() == Explain_node::EXPLAIN_UNION)
+  {
+    Explain_union *u= (Explain_union*)node;
+    select_id= u->get_select_id();
+    if (unions.elements() <= select_id)
+      unions.resize(MY_MAX(select_id+1, unions.elements()*2), NULL);
+
+    Explain_union *old_node;
+    if ((old_node= get_union(select_id)))
+      delete old_node;
+
+    unions.at(select_id)= u;
+  }
+  else
+  {
+    Explain_select *sel= (Explain_select*)node;
+    if (sel->select_id == FAKE_SELECT_LEX_ID)
+    {
+      DBUG_ASSERT(0); // this is a "fake select" from a UNION.
+    }
+    else
+    {
+      select_id= sel->select_id;
+      Explain_select *old_node;
+
+      if (selects.elements() <= select_id)
+        selects.resize(MY_MAX(select_id+1, selects.elements()*2), NULL);
+
+      if ((old_node= get_select(select_id)))
+        delete old_node;
+
+      selects.at(select_id)= sel;
+    }
+  }
+}
+
+
+void Explain_query::add_insert_plan(Explain_insert *insert_plan_arg)
+{
+  insert_plan= insert_plan_arg;
+  query_plan_ready();
+}
+
+
+void Explain_query::add_upd_del_plan(Explain_update *upd_del_plan_arg)
+{
+  upd_del_plan= upd_del_plan_arg;
+  query_plan_ready();
+}
+
+
+void Explain_query::query_plan_ready()
+{
+  optimization_time_tracker.stop_tracking(stmt_thd);
+
+  if (!apc_enabled)
+    stmt_thd->apc_target.enable();
+  apc_enabled= true;
+#ifndef DBUG_OFF
+  can_print_json= true;
+#endif
+}
+
+
+void Explain_query::notify_tables_are_closed()
+{
+  /*
+    Disable processing of SHOW EXPLAIN|ANALYZE. The query is about to close
+    the tables it is using, which will make it impossible to print Item*
+    values. See sql_explain.h:ExplainDataStructureLifetime for details.
+  */
+  if (apc_enabled)
+  {
+    stmt_thd->apc_target.disable();
+    apc_enabled= false;
+#ifndef DBUG_OFF
+    can_print_json= false;
+#endif
+  }
+}
+
+
+/*
+  Send EXPLAIN output to the client.
+*/
+
+int Explain_query::send_explain(THD *thd, bool extended)
+{
+  select_result *result;
+  LEX *lex= thd->lex;
+ 
+  if (!(result= new (thd->mem_root) select_send(thd)) || 
+      thd->send_explain_fields(result, lex->describe, lex->analyze_stmt))
+    return 1;
+
+  int res= 0;
+  if (thd->lex->explain_json)
+    print_explain_json(result, thd->lex->analyze_stmt);
+  else
+  {
+    res= print_explain(result, lex->describe, thd->lex->analyze_stmt);
+    if (extended)
+    {
+      char buff[1024];
+      String str(buff,(uint32) sizeof(buff), system_charset_info);
+                 str.length(0);
+     /*
+       The warnings system requires input in utf8, @see
+        mysqld_show_warnings().
+     */
+     lex->unit.print(&str, QT_EXPLAIN_EXTENDED);
+                     push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
+                     ER_YES, str.c_ptr_safe());
+    }
+  }
+  if (res)
+    result->abort_result_set();
+  else
+    result->send_eof();
+
+  return res;
+}
+
+
+
+/*
+  The main entry point to print EXPLAIN of the entire query
+*/
+
+int Explain_query::print_explain(select_result_sink *output, 
+                                 uint8 explain_flags, bool is_analyze)
+{
+  if (upd_del_plan)
+  {
+    upd_del_plan->print_explain(this, output, explain_flags, is_analyze);
+    return 0;
+  }
+  else if (insert_plan)
+  {
+    insert_plan->print_explain(this, output, explain_flags, is_analyze);
+    return 0;
+  }
+  else
+  {
+    /* Start printing from node with id=1 */
+    Explain_node *node= get_node(1);
+    if (!node)
+      return 1; /* No query plan */
+    return node->print_explain(this, output, explain_flags, is_analyze);
+  }
+}
+
+
+int Explain_query::print_explain_json(select_result_sink *output,
+                                      bool is_analyze,
+                                      ulonglong query_time_in_progress_ms)
+{
+  Json_writer writer;
+
+#ifndef DBUG_OFF
+  DBUG_ASSERT(can_print_json);
+#endif
+
+  writer.start_object();
+
+  if (is_analyze)
+  {
+    if (query_time_in_progress_ms > 0){
+      writer.add_member("r_query_time_in_progress_ms").
+            add_ull(query_time_in_progress_ms);
+    }
+
+    print_query_optimization_json(&writer);
+  }
+
+  bool plan_found = print_query_blocks_json(&writer, is_analyze);
+  writer.end_object();
+
+  if( plan_found )
+  {
+    send_explain_json_to_output(&writer, output);
+  }
+  
+  return 0;
+}
+
+void Explain_query::print_query_optimization_json(Json_writer *writer)
+{
+  if (optimization_time_tracker.has_timed_statistics())
+  {
+    // if more timers are added, move the query_optimization member 
+    // outside the if statement
+    writer->add_member("query_optimization").start_object();
+    writer->add_member("r_total_time_ms").
+            add_double(optimization_time_tracker.get_time_ms());
+    writer->end_object(); 
+  }
+}
+
+bool Explain_query::print_query_blocks_json(Json_writer *writer, const bool is_analyze)
+{
+  if (upd_del_plan)
+    upd_del_plan->print_explain_json(this, writer, is_analyze);
+  else if (insert_plan)
+    insert_plan->print_explain_json(this, writer, is_analyze);
+  else
+  {
+    /* Start printing from root node with id=1 */
+    Explain_node *node= get_node(1);
+    if (!node)
+      return false; /* No query plan */
+    node->print_explain_json(this, writer, is_analyze);
+  }
+
+  return true;
+}
+
+void Explain_query::send_explain_json_to_output(Json_writer *writer, 
+                                                select_result_sink *output)
+{
+  CHARSET_INFO *cs= system_charset_info;
+  List<Item> item_list;
+  const String *buf= writer->output.get_string();
+  THD *thd= output->thd;
+  item_list.push_back(new (thd->mem_root)
+                      Item_string(thd, buf->ptr(), buf->length(), cs),
+                      thd->mem_root);
+  output->send_data(item_list);
+} 
+
+bool print_explain_for_slow_log(LEX *lex, THD *thd, String *str)
+{
+  return lex->explain->print_explain_str(thd, str, /*is_analyze*/ true);
+}
+
+
+/* 
+  Return tabular EXPLAIN output as a text string
+*/
+
+bool Explain_query::print_explain_str(THD *thd, String *out_str,
+                                      bool is_analyze)
+{
+  List<Item> fields;
+  thd->make_explain_field_list(fields, thd->lex->describe, is_analyze);
+
+  select_result_text_buffer output_buf(thd);
+  output_buf.send_result_set_metadata(fields, thd->lex->describe);
+  if (print_explain(&output_buf, thd->lex->describe, is_analyze))
+    return true;
+  output_buf.save_to(out_str);
+  return false;
+}
+
+
+static void push_str(THD *thd, List<Item> *item_list, const char *str)
+{
+  item_list->push_back(new (thd->mem_root) Item_string_sys(thd, str),
+                       thd->mem_root);
+}
+
+
+static void push_string(THD *thd, List<Item> *item_list, String *str)
+{
+  item_list->push_back(new (thd->mem_root)
+                       Item_string_sys(thd, str->ptr(), str->length()),
+                       thd->mem_root);
+}
+
+static void push_string_list(THD *thd, List<Item> *item_list,
+                             String_list &lines, String *buf)
+{
+  List_iterator_fast<char> it(lines);
+  char *line;
+  bool first= true;
+  while ((line= it++))
+  {
+    if (first)
+      first= false;
+    else
+      buf->append(',');
+
+    buf->append(line, strlen(line));
+  }
+  push_string(thd, item_list, buf);
+}
+
+
+/*
+  Print an EXPLAIN output row, based on information provided in the parameters
+
+  @note
+    Parameters that may have NULL value in EXPLAIN output, should be passed
+    (char*)NULL.
+
+  @return 
+    0  - OK
+    1  - OOM Error
+*/
+
+static
+int print_explain_row(select_result_sink *result,
+                      uint8 options, bool is_analyze,
+                      uint select_number,
+                      const char *select_type,
+                      const char *table_name,
+                      const char *partitions,
+                      enum join_type jtype,
+                      String_list *possible_keys,
+                      const char *index,
+                      const char *key_len,
+                      const char *ref,
+                      ha_rows *rows,
+                      double *r_rows,
+                      double r_filtered,
+                      const char *extra)
+{
+  THD *thd= result->thd;
+  MEM_ROOT *mem_root= thd->mem_root;
+  Item *item_null= new (mem_root) Item_null(thd);
+  List<Item> item_list;
+  Item *item;
+
+  if (!select_type[0])
+    return 0;
+
+  item_list.push_back(new (mem_root) Item_int(thd, (int32) select_number),
+                      mem_root);
+  item_list.push_back(new (mem_root) Item_string_sys(thd, select_type),
+                      mem_root);
+  item_list.push_back(new (mem_root) Item_string_sys(thd, table_name),
+                      mem_root);
+  if (options & DESCRIBE_PARTITIONS)
+  {
+    if (partitions)
+    {
+      item_list.push_back(new (mem_root) Item_string_sys(thd, partitions),
+                          mem_root);
+    }
+    else
+      item_list.push_back(item_null, mem_root);
+  }
+  
+  const char *jtype_str= join_type_str[jtype];
+  item_list.push_back(new (mem_root) Item_string_sys(thd, jtype_str),
+                      mem_root);
+  
+  /* 'possible_keys'
+     The buffer must not be deallocated before we call send_data, otherwise
+     we may end up reading freed memory.
+  */
+  StringBuffer<64> possible_keys_buf;
+  if (possible_keys && !possible_keys->is_empty())
+  {
+    push_string_list(thd, &item_list, *possible_keys, &possible_keys_buf);
+  }
+  else
+    item_list.push_back(item_null, mem_root);
+  
+  /* 'index */
+  item= index ? new (mem_root) Item_string_sys(thd, index) : item_null;
+  item_list.push_back(item, mem_root);
+  
+  /* 'key_len */
+  item= key_len ? new (mem_root) Item_string_sys(thd, key_len) : item_null;
+  item_list.push_back(item, mem_root);
+  
+  /* 'ref' */
+  item= ref ? new (mem_root) Item_string_sys(thd, ref) : item_null;
+  item_list.push_back(item, mem_root);
+
+  /* 'rows' */
+  StringBuffer<64> rows_str;
+  if (rows)
+  {
+    rows_str.append_ulonglong((ulonglong)(*rows));
+    item_list.push_back(new (mem_root)
+                        Item_string_sys(thd, rows_str.ptr(),
+                                        rows_str.length()), mem_root);
+  }
+  else
+    item_list.push_back(item_null, mem_root);
+  
+  /* 'r_rows' */
+  StringBuffer<64> r_rows_str;
+  if (is_analyze)
+  {
+    if (r_rows)
+    {
+      Item_float *fl= new (mem_root) Item_float(thd, *r_rows, 2);
+      String tmp;
+      String *res= fl->val_str(&tmp);
+      r_rows_str.append(*res);
+      item_list.push_back(new (mem_root)
+                          Item_string_sys(thd, r_rows_str.ptr(),
+                                          r_rows_str.length()), mem_root);
+    }
+    else
+      item_list.push_back(item_null, mem_root);
+  }
+
+  /* 'filtered' */
+  const double filtered=100.0;
+  if (options & DESCRIBE_EXTENDED || is_analyze)
+    item_list.push_back(new (mem_root) Item_float(thd, filtered, 2), mem_root);
+  
+  /* 'r_filtered' */
+  if (is_analyze)
+    item_list.push_back(new (mem_root) Item_float(thd, r_filtered, 2),
+                        mem_root);
+  
+  /* 'Extra' */
+  if (extra)
+    item_list.push_back(new (mem_root) Item_string_sys(thd, extra), mem_root);
+  else
+    item_list.push_back(item_null, mem_root);
+
+  if (result->send_data(item_list))
+    return 1;
+  return 0;
+}
+
+
+
+
+uint Explain_union::make_union_table_name(char *buf)
+{
+  uint childno= 0;
+  uint len, lastop= 0;
+  LEX_CSTRING type;
+  switch (operation)
+  {
+    case OP_MIX:
+      lex_string_set3(&type, STRING_WITH_LEN("<unit"));
+      break;
+    case OP_UNION:
+      lex_string_set3(&type, STRING_WITH_LEN("<union"));
+      break;
+    case OP_INTERSECT:
+      lex_string_set3(&type, STRING_WITH_LEN("<intersect"));
+      break;
+    case OP_EXCEPT:
+      lex_string_set3(&type, STRING_WITH_LEN("<except"));
+      break;
+    default:
+      DBUG_ASSERT(0);
+      type.str= NULL;
+      type.length= 0;
+  }
+  memcpy(buf, type.str, (len= (uint)type.length));
+
+  for (; childno < union_members.elements() && len + lastop + 5 < NAME_LEN;
+       childno++)
+  {
+    len+= lastop;
+    lastop= (uint)my_snprintf(buf + len, NAME_LEN - len,
+                        "%u,", union_members.at(childno));
+  }
+
+  if (childno < union_members.elements() || len + lastop >= NAME_LEN)
+  {
+    memcpy(buf + len, STRING_WITH_LEN("...>") + 1);
+    len+= 4;
+  }
+  else
+  {
+    len+= lastop;
+    buf[len - 1]= '>';  // change ',' to '>'
+  }
+  return len;
+}
+
+
+int Explain_union::print_explain(Explain_query *query, 
+                                 select_result_sink *output,
+                                 uint8 explain_flags, 
+                                 bool is_analyze)
+{
+  THD *thd= output->thd;
+  MEM_ROOT *mem_root= thd->mem_root;
+  char table_name_buffer[SAFE_NAME_LEN];
+
+  /* print all UNION children, in order */
+  for (int i= 0; i < (int) union_members.elements(); i++)
+  {
+    Explain_select *sel= query->get_select(union_members.at(i));
+    sel->print_explain(query, output, explain_flags, is_analyze);
+  }
+
+  if (!using_tmp)
+    return 0;
+
+  /* Print a line with "UNIT RESULT" */
+  List<Item> item_list;
+  Item *item_null= new (mem_root) Item_null(thd);
+
+  /* `id` column */
+  item_list.push_back(item_null, mem_root);
+
+  /* `select_type` column */
+  push_str(thd, &item_list, fake_select_type);
+
+  /* `table` column: something like "<union1,2>" */
+  uint len= make_union_table_name(table_name_buffer);
+  item_list.push_back(new (mem_root)
+                      Item_string_sys(thd, table_name_buffer, len),
+                      mem_root);
+  
+  /* `partitions` column */
+  if (explain_flags & DESCRIBE_PARTITIONS)
+    item_list.push_back(item_null, mem_root);
+
+  /* `type` column */
+  push_str(thd, &item_list, join_type_str[JT_ALL]);
+
+  /* `possible_keys` column */
+  item_list.push_back(item_null, mem_root);
+
+  /* `key` */
+  item_list.push_back(item_null, mem_root);
+
+  /* `key_len` */
+  item_list.push_back(item_null, mem_root);
+
+  /* `ref` */
+  item_list.push_back(item_null, mem_root);
+ 
+  /* `rows` */
+  item_list.push_back(item_null, mem_root);
+  
+  /* `r_rows` */
+  StringBuffer<64> r_rows_str;
+  if (is_analyze)
+  {
+    double avg_rows= fake_select_lex_tracker.get_avg_rows();
+    Item_float *fl= new (mem_root) Item_float(thd, avg_rows, 2);
+    String tmp;
+    String *res= fl->val_str(&tmp);
+    r_rows_str.append(*res);
+    item_list.push_back(new (mem_root)
+                        Item_string_sys(thd, r_rows_str.ptr(),
+                                        r_rows_str.length()), mem_root);
+  }
+
+  /* `filtered` */
+  if (explain_flags & DESCRIBE_EXTENDED || is_analyze)
+    item_list.push_back(item_null, mem_root);
+
+  /* `r_filtered` */
+  if (is_analyze)
+    item_list.push_back(item_null, mem_root);
+
+  /* `Extra` */
+  StringBuffer<256> extra_buf;
+  if (using_filesort)
+  {
+    extra_buf.append(STRING_WITH_LEN("Using filesort"));
+  }
+  item_list.push_back(new (mem_root)
+                      Item_string_sys(thd, extra_buf.ptr(),
+                                      extra_buf.length()),
+                      mem_root);
+
+  //output->unit.offset_limit_cnt= 0; 
+  if (output->send_data(item_list))
+    return 1;
+  
+  /*
+    Print all subquery children (UNION children have already been printed at
+    the start of this function)
+  */
+  return print_explain_for_children(query, output, explain_flags, is_analyze);
+}
+
+
+void Explain_union::print_explain_json(Explain_query *query, 
+                                       Json_writer *writer, bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+  char table_name_buffer[SAFE_NAME_LEN];
+  
+  bool started_object= print_explain_json_cache(writer, is_analyze);
+
+  writer->add_member("query_block").start_object();
+  
+  if (is_recursive_cte)
+    writer->add_member("recursive_union").start_object();
+  else
+    writer->add_member("union_result").start_object();
+
+  if (using_tmp)
+  {
+    make_union_table_name(table_name_buffer);
+    writer->add_member("table_name").add_str(table_name_buffer);
+    writer->add_member("access_type").add_str("ALL"); // not very useful
+
+    /* r_loops (not present in tabular output) */
+    if (is_analyze)
+    {
+      writer->add_member("r_loops").add_ll(
+          fake_select_lex_tracker.get_loops());
+    }
+
+    /* `r_rows` */
+    if (is_analyze)
+    {
+      writer->add_member("r_rows");
+      if (fake_select_lex_tracker.has_scans())
+        writer->add_double(fake_select_lex_tracker.get_avg_rows());
+      else
+        writer->add_null();
+    }
+  }
+  writer->add_member("query_specifications").start_array();
+
+  for (int i= 0; i < (int) union_members.elements(); i++)
+  {
+    writer->start_object();
+    //writer->add_member("dependent").add_str("TODO");
+    //writer->add_member("cacheable").add_str("TODO");
+    Explain_select *sel= query->get_select(union_members.at(i));
+    sel->print_explain_json(query, writer, is_analyze);
+    writer->end_object();
+  }
+  writer->end_array();
+
+  print_explain_json_for_children(query, writer, is_analyze);
+
+  writer->end_object(); // union_result
+  writer->end_object(); // query_block
+
+  if (started_object)
+    writer->end_object();
+}
+
+
+/*
+  Print EXPLAINs for all children nodes (i.e. for subqueries)
+*/
+
+int Explain_node::print_explain_for_children(Explain_query *query, 
+                                             select_result_sink *output,
+                                             uint8 explain_flags, 
+                                             bool is_analyze)
+{
+  for (int i= 0; i < (int) children.elements(); i++)
+  {
+    Explain_node *node= query->get_node(children.at(i));
+    /*
+      Note: node may not be present because for certain kinds of subqueries,
+      the optimizer is not able to see that they were eliminated.
+    */
+    if (node && node->print_explain(query, output, explain_flags, is_analyze))
+      return 1;
+  }
+  return 0;
+}
+
+bool Explain_basic_join::add_table(Explain_table_access *tab, Explain_query *query)
+{
+  if (!join_tabs)
+  {
+    n_join_tabs= 0;
+    if (!(join_tabs= ((Explain_table_access**)
+                      alloc_root(query->mem_root,
+                                 sizeof(Explain_table_access*) *
+                                 MAX_TABLES))))
+      return true;
+  }
+  join_tabs[n_join_tabs++]= tab;
+  return false;
+}
+
+/*
+  This tells whether a child subquery should be printed in JSON output.
+
+  Derived tables and Non-merged semi-joins should not be printed, because they
+  are printed inline in Explain_table_access.
+*/
+bool is_connection_printable_in_json(enum Explain_node::explain_connection_type type)
+{
+  return (type != Explain_node::EXPLAIN_NODE_DERIVED && 
+          type != Explain_node::EXPLAIN_NODE_NON_MERGED_SJ);
+}
+
+
+void Explain_node::print_explain_json_for_children(Explain_query *query, 
+                                                  Json_writer *writer,
+                                                  bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+  
+  bool started= false;
+  for (int i= 0; i < (int) children.elements(); i++)
+  {
+    Explain_node *node= query->get_node(children.at(i));
+    
+    /*
+      Note: node may not be present because for certain kinds of subqueries,
+      the optimizer is not able to see that they were eliminated.
+    */
+    if (!node)
+      continue;
+
+    /* Derived tables are printed inside Explain_table_access objects */
+    if (!is_connection_printable_in_json(node->connection_type))
+      continue;
+
+    if (!started)
+    {
+      writer->add_member("subqueries").start_array();
+      started= true;
+    }
+
+    writer->start_object();
+    node->print_explain_json(query, writer, is_analyze);
+    writer->end_object();
+  }
+
+  if (started)
+    writer->end_array();
+}
+
+
+bool Explain_node::print_explain_json_cache(Json_writer *writer,
+                                            bool is_analyze)
+{
+  if (cache_tracker)
+  {
+    cache_tracker->fetch_current_stats();
+    writer->add_member("expression_cache").start_object();
+    if (cache_tracker->state != Expression_cache_tracker::OK)
+    {
+      writer->add_member("state").
+        add_str(Expression_cache_tracker::state_str[cache_tracker->state]);
+    }
+
+    if (is_analyze)
+    {
+      longlong cache_reads= cache_tracker->hit + cache_tracker->miss;
+      writer->add_member("r_loops").add_ll(cache_reads);
+      if (cache_reads != 0) 
+      {
+        double hit_ratio= double(cache_tracker->hit) / cache_reads * 100.0;
+        writer->add_member("r_hit_ratio").add_double(hit_ratio);
+      }
+    }
+    return true;
+  }
+  return false;
+}
+
+
+Explain_basic_join::~Explain_basic_join()
+{
+  if (join_tabs)
+  {
+    for (uint i= 0; i< n_join_tabs; i++)
+      delete join_tabs[i];
+  }
+} 
+
+
+int Explain_select::print_explain(Explain_query *query, 
+                                  select_result_sink *output,
+                                  uint8 explain_flags, bool is_analyze)
+{
+  THD *thd= output->thd;
+  MEM_ROOT *mem_root= thd->mem_root;
+
+  if (select_type == pushed_derived_text || select_type == pushed_select_text)
+  {
+     print_explain_message_line(output, explain_flags, is_analyze,
+                                select_id /*select number*/,
+                                select_type,
+                                NULL, /* rows */
+                                NULL);
+  }
+  else if (message)
+  {
+    List<Item> item_list;
+    Item *item_null= new (mem_root) Item_null(thd);
+
+    item_list.push_back(new (mem_root) Item_int(thd, (int32) select_id),
+                        mem_root);
+    item_list.push_back(new (mem_root) Item_string_sys(thd, select_type),
+                        mem_root);
+    for (uint i=0 ; i < 7; i++)
+      item_list.push_back(item_null, mem_root);
+    if (explain_flags & DESCRIBE_PARTITIONS)
+      item_list.push_back(item_null, mem_root);
+
+    /* filtered */
+    if (is_analyze || explain_flags & DESCRIBE_EXTENDED)
+      item_list.push_back(item_null, mem_root);
+    
+    if (is_analyze)
+    {
+      /* r_rows, r_filtered */
+      item_list.push_back(item_null, mem_root);
+      item_list.push_back(item_null, mem_root);
+    }
+
+    item_list.push_back(new (mem_root) Item_string_sys(thd, message),
+                        mem_root);
+
+    if (output->send_data(item_list))
+      return 1;
+  }
+  else
+  {
+    bool using_tmp= false;
+    bool using_fs= false;
+
+    for (Explain_aggr_node *node= aggr_tree; node; node= node->child)
+    {
+      switch (node->get_type())
+      {
+        case AGGR_OP_TEMP_TABLE:
+          using_tmp= true;
+          break;
+        case AGGR_OP_FILESORT:
+          using_fs= true;
+          break;
+        default:
+          break;
+      }
+    }
+
+    for (uint i=0; i< n_join_tabs; i++)
+    {
+      join_tabs[i]->print_explain(output, explain_flags, is_analyze, select_id,
+                                  select_type, using_tmp, using_fs);
+      if (i == 0)
+      {
+        /* 
+          "Using temporary; Using filesort" should only be shown near the 1st
+          table
+        */
+        using_tmp= false;
+        using_fs= false;
+      }
+    }
+    for (uint i=0; i< n_join_tabs; i++)
+    {
+      Explain_basic_join* nest;
+      if ((nest= join_tabs[i]->sjm_nest))
+        nest->print_explain(query, output, explain_flags, is_analyze);
+    }
+  }
+
+  return print_explain_for_children(query, output, explain_flags, is_analyze);
+}
+
+
+int Explain_basic_join::print_explain(Explain_query *query, 
+                                      select_result_sink *output,
+                                      uint8 explain_flags, bool is_analyze)
+{
+  for (uint i=0; i< n_join_tabs; i++)
+  {
+    if (join_tabs[i]->print_explain(output, explain_flags, is_analyze, 
+                                    select_id,
+                                    "MATERIALIZED" /*select_type*/, 
+                                    FALSE /*using temporary*/, 
+                                    FALSE /*using filesort*/))
+      return 1;
+  }
+  return 0;
+}
+
+
+void Explain_select::add_linkage(Json_writer *writer)
+{
+  const char *operation= NULL;
+  switch (linkage)
+  {
+     case UNION_TYPE:
+       operation= "UNION";
+       break;
+     case INTERSECT_TYPE:
+       operation= "INTERSECT";
+       break;
+     case EXCEPT_TYPE:
+       operation= "EXCEPT";
+       break;
+     default:
+       // It is the first or the only SELECT => no operation
+       break;
+  }
+  if (operation)
+    writer->add_member("operation").add_str(operation);
+}
+
+void Explain_select::print_explain_json(Explain_query *query, 
+                                        Json_writer *writer, bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+  
+  bool started_cache= print_explain_json_cache(writer, is_analyze);
+
+  if (message ||
+      select_type == pushed_derived_text ||
+      select_type == pushed_select_text)
+  {
+    writer->add_member("query_block").start_object();
+    writer->add_member("select_id").add_ll(select_id);
+    add_linkage(writer);
+
+    writer->add_member("table").start_object();
+    writer->add_member("message").add_str(select_type == pushed_derived_text ?
+                                          "Pushed derived" :
+                                          select_type == pushed_select_text ?
+                                          "Pushed select" :
+                                          message);
+    writer->end_object();
+
+    print_explain_json_for_children(query, writer, is_analyze);
+    writer->end_object();
+  }
+  else
+  {
+    writer->add_member("query_block").start_object();
+    writer->add_member("select_id").add_ll(select_id);
+    add_linkage(writer);
+
+    if (is_analyze && time_tracker.get_loops())
+    {
+      writer->add_member("r_loops").add_ll(time_tracker.get_loops());
+      if (time_tracker.has_timed_statistics())
+      {
+        writer->add_member("r_total_time_ms").
+                add_double(time_tracker.get_time_ms());
+      }
+    }
+
+    if (exec_const_cond)
+    {
+      writer->add_member("const_condition");
+      write_item(writer, exec_const_cond);
+    }
+    if (outer_ref_cond)
+    {
+      writer->add_member("outer_ref_condition");
+      write_item(writer, outer_ref_cond);
+    }
+    if (pseudo_bits_cond)
+    {
+      writer->add_member("pseudo_bits_condition");
+      write_item(writer, pseudo_bits_cond);
+    }
+
+    /* we do not print HAVING which always evaluates to TRUE */
+    if (having || (having_value == Item::COND_FALSE))
+    {
+      writer->add_member("having_condition");
+      if (likely(having))
+        write_item(writer, having);
+      else
+      {
+        /* Normally we should not go this branch, left just for safety */
+        DBUG_ASSERT(having_value == Item::COND_FALSE);
+        writer->add_str("0");
+      }
+    }
+
+    int started_objects= 0;
+    
+    Explain_aggr_node *node= aggr_tree;
+
+    for (; node; node= node->child)
+    {
+      switch (node->get_type())
+      {
+        case AGGR_OP_TEMP_TABLE:
+          writer->add_member("temporary_table").start_object();
+          break;
+        case AGGR_OP_FILESORT:
+        {
+          writer->add_member("filesort").start_object();
+          auto aggr_node= (Explain_aggr_filesort*)node;
+          aggr_node->print_json_members(writer, is_analyze);
+          break;
+        }
+        case AGGR_OP_REMOVE_DUPLICATES:
+          writer->add_member("duplicate_removal").start_object();
+          break;
+        case AGGR_OP_WINDOW_FUNCS:
+        {
+          //TODO: make print_json_members virtual?
+          writer->add_member("window_functions_computation").start_object();
+          auto aggr_node= (Explain_aggr_window_funcs*)node;
+          aggr_node->print_json_members(writer, is_analyze);
+          break;
+        }
+        default:
+          DBUG_ASSERT(0);
+      }
+      started_objects++;
+    }
+    
+    Explain_basic_join::print_explain_json_interns(query, writer, is_analyze);
+
+    for (;started_objects; started_objects--)
+      writer->end_object();
+
+    writer->end_object();
+  }
+
+  if (started_cache)
+    writer->end_object();
+}
+
+
+Explain_aggr_filesort::Explain_aggr_filesort(MEM_ROOT *mem_root, 
+                                             bool is_analyze,
+                                             Filesort *filesort)
+ : tracker(is_analyze)
+{
+  child= NULL;
+  for (ORDER *ord= filesort->order; ord; ord= ord->next)
+  {
+    sort_items.push_back(ord->item[0], mem_root);
+    sort_directions.push_back(&ord->direction, mem_root);
+  }
+  filesort->tracker= &tracker;
+}
+
+
+void Explain_aggr_filesort::print_json_members(Json_writer *writer, 
+                                               bool is_analyze)
+{
+  char item_buf[256];
+  String str(item_buf, sizeof(item_buf), &my_charset_bin);
+  str.length(0);
+  
+  List_iterator_fast<Item> it(sort_items);
+  List_iterator_fast<ORDER::enum_order> it_dir(sort_directions);
+  Item* item;
+  ORDER::enum_order *direction;
+  bool first= true;
+  while ((item= it++))
+  {
+    direction= it_dir++;
+    if (first)
+      first= false;
+    else
+    {
+      str.append(STRING_WITH_LEN(", "));
+    }
+    append_item_to_str(&str, item);
+    if (*direction == ORDER::ORDER_DESC)
+      str.append(STRING_WITH_LEN(" desc"));
+  }
+
+  writer->add_member("sort_key").add_str(str.c_ptr_safe());
+
+  if (is_analyze)
+    tracker.print_json_members(writer);
+}
+
+
+void Explain_aggr_window_funcs::print_json_members(Json_writer *writer, 
+                                                   bool is_analyze)
+{
+  Explain_aggr_filesort *srt;
+  List_iterator<Explain_aggr_filesort> it(sorts);
+  Json_writer_array sorts(writer, "sorts");
+  while ((srt= it++))
+  {
+    Json_writer_object sort(writer);
+    Json_writer_object filesort(writer, "filesort");
+    srt->print_json_members(writer, is_analyze);
+  }
+}
+
+
+void Explain_basic_join::print_explain_json(Explain_query *query, 
+                                            Json_writer *writer, 
+                                            bool is_analyze)
+{
+  writer->add_member("query_block").start_object();
+  writer->add_member("select_id").add_ll(select_id);
+  
+  print_explain_json_interns(query, writer, is_analyze);
+
+  writer->end_object();
+}
+
+
+void Explain_basic_join::
+print_explain_json_interns(Explain_query *query, 
+                           Json_writer *writer, 
+                           bool is_analyze)
+{
+  {
+    Json_writer_array loop(writer, "nested_loop");
+    for (uint i=0; i< n_join_tabs; i++)
+    {
+      if (join_tabs[i]->start_dups_weedout)
+      {
+        writer->start_object();
+        writer->add_member("duplicates_removal");
+        writer->start_array();
+      }
+
+      join_tabs[i]->print_explain_json(query, writer, is_analyze);
+
+      if (join_tabs[i]->end_dups_weedout)
+      {
+        writer->end_array();
+        writer->end_object();
+      }
+    }
+  } // "nested_loop"
+  print_explain_json_for_children(query, writer, is_analyze);
+}
+
+
+void Explain_table_access::push_extra(enum explain_extra_tag extra_tag)
+{
+  extra_tags.append(extra_tag);
+}
+
+
+/*
+  Put the contents of 'key' field of EXPLAIN otuput into key_str.
+
+  It is surprisingly complex:
+  - hash join shows #hash#used_key
+  - quick selects that use single index will print index name
+*/
+
+void Explain_table_access::fill_key_str(String *key_str, bool is_json) const
+{
+  CHARSET_INFO *cs= system_charset_info;
+  bool is_hj= (type == JT_HASH || type == JT_HASH_NEXT || 
+               type == JT_HASH_RANGE || type == JT_HASH_INDEX_MERGE);
+  LEX_CSTRING hash_key_prefix= { STRING_WITH_LEN("#hash#") };
+  const char *key_name;
+
+  if ((key_name= key.get_key_name()))
+  {
+    if (is_hj)
+      key_str->append(hash_key_prefix.str, hash_key_prefix.length, cs);
+
+    key_str->append(key_name, strlen(key_name));
+
+    if (is_hj && type != JT_HASH)
+      key_str->append(':');
+  }
+  
+  if (quick_info)
+  {
+    StringBuffer<64> buf2;
+    if (is_json)
+      quick_info->print_extra_recursive(&buf2);
+    else
+      quick_info->print_key(&buf2);
+    key_str->append(buf2);
+  }
+  if (type == JT_HASH_NEXT)
+  {
+    key_name= hash_next_key.get_key_name();
+    key_str->append(key_name, strlen(key_name));
+  }
+}
+
+
+/*
+  Fill "key_length".
+   - this is just used key length for ref/range 
+   - for index_merge, it is a comma-separated list of lengths.
+   - for hash join, it is key_len:pseudo_key_len
+   - [tabular form only] rowid filter length is added after "|".
+
+  In JSON, we consider this column to be legacy, it is superceded by
+  used_key_parts.
+*/
+
+void Explain_table_access::fill_key_len_str(String *key_len_str,
+                                            bool is_json) const
+{
+  bool is_hj= (type == JT_HASH || type == JT_HASH_NEXT || 
+               type == JT_HASH_RANGE || type == JT_HASH_INDEX_MERGE);
+  if (key.get_key_len() != (uint)-1)
+  {
+    char buf[64];
+    size_t length;
+    length= longlong10_to_str(key.get_key_len(), buf, 10) - buf;
+    key_len_str->append(buf, length);
+    if (is_hj && type != JT_HASH)
+      key_len_str->append(':');
+  }
+
+  if (quick_info)
+  {
+    StringBuffer<64> buf2;
+    quick_info->print_key_len(&buf2);
+    key_len_str->append(buf2);
+  } 
+
+  if (type == JT_HASH_NEXT)
+  {
+    char buf[64];
+    size_t length;
+    length= longlong10_to_str(hash_next_key.get_key_len(), buf, 10) - buf;
+    key_len_str->append(buf, length);
+  }
+
+  if (!is_json && rowid_filter)
+  {
+    key_len_str->append('|');
+    StringBuffer<64> filter_key_len;
+    rowid_filter->quick->print_key_len(&filter_key_len);
+    key_len_str->append(filter_key_len);
+  }
+}
+
+
+bool Explain_index_use::set(MEM_ROOT *mem_root, KEY *key, uint key_len_arg)
+{
+  if (set_pseudo_key(mem_root, key->name.str))
+    return 1;
+
+  key_len= key_len_arg;
+  uint len= 0;
+  for (uint i= 0; i < key->usable_key_parts; i++)
+  {
+    if (!key_parts_list.append_str(mem_root,
+                                   key->key_part[i].field->field_name.str))
+      return 1;
+    len += key->key_part[i].store_length;
+    if (len >= key_len_arg)
+      break;
+  }
+  return 0;
+}
+
+
+bool Explain_index_use::set_pseudo_key(MEM_ROOT *root, const char* key_name_arg)
+{
+  if (key_name_arg)
+  {
+    if (!(key_name= strdup_root(root, key_name_arg)))
+      return 1;
+  }
+  else
+    key_name= NULL;
+  key_len= ~(uint) 0;
+  return 0;
+}
+
+
+/*
+  Given r_filtered% from join buffer condition and join condition, produce a
+  combined r_filtered% number. This is needed for tabular EXPLAIN output which
+  has only one cell for r_filtered value.
+*/
+
+double Explain_table_access::get_r_filtered()
+{
+  double r_filtered= tracker.get_filtered_after_where();
+  if (bka_type.is_using_jbuf())
+    r_filtered *= jbuf_tracker.get_filtered_after_where();
+  return r_filtered;
+}
+
+
+int Explain_table_access::print_explain(select_result_sink *output, uint8 explain_flags, 
+                                        bool is_analyze,
+                                        uint select_id, const char *select_type,
+                                        bool using_temporary, bool using_filesort)
+{
+  THD *thd= output->thd; // note: for SHOW EXPLAIN, this is target thd.
+  MEM_ROOT *mem_root= thd->mem_root;
+
+  List<Item> item_list;
+  Item *item_null= new (mem_root) Item_null(thd);
+  
+  /* `id` column */
+  item_list.push_back(new (mem_root) Item_int(thd, (int32) select_id),
+                      mem_root);
+
+  /* `select_type` column */
+  push_str(thd, &item_list, select_type);
+
+  /* `table` column */
+  push_string(thd, &item_list, &table_name);
+  
+  /* `partitions` column */
+  if (explain_flags & DESCRIBE_PARTITIONS)
+  {
+    if (used_partitions_set)
+    {
+      push_string(thd, &item_list, &used_partitions);
+    }
+    else
+      item_list.push_back(item_null, mem_root);
+  }
+
+  /* `type` column */
+   StringBuffer<64> join_type_buf;
+  if (rowid_filter == NULL)
+    push_str(thd, &item_list, join_type_str[type]);
+  else
+  {
+    join_type_buf.append(join_type_str[type], strlen(join_type_str[type]));
+    join_type_buf.append(STRING_WITH_LEN("|filter"));
+    item_list.push_back(new (mem_root)
+                        Item_string_sys(thd, join_type_buf.ptr(),
+                                             join_type_buf.length()),
+                        mem_root);
+  }
+
+  /* `possible_keys` column */
+  StringBuffer<64> possible_keys_buf;
+  if (possible_keys.is_empty())
+    item_list.push_back(item_null, mem_root);
+  else
+    push_string_list(thd, &item_list, possible_keys, &possible_keys_buf);
+
+  /* `key` */
+  StringBuffer<64> key_str;
+  fill_key_str(&key_str, false);
+
+  if (rowid_filter)
+  {
+    key_str.append('|');
+    StringBuffer<64> rowid_key_str;
+    rowid_filter->quick->print_key(&rowid_key_str);
+    key_str.append(rowid_key_str);
+  }
+  
+  if (key_str.length() > 0)
+    push_string(thd, &item_list, &key_str);
+  else
+    item_list.push_back(item_null, mem_root);
+
+  /* `key_len` */
+  StringBuffer<64> key_len_str;
+  fill_key_len_str(&key_len_str, false);
+
+  if (key_len_str.length() > 0)
+    push_string(thd, &item_list, &key_len_str);
+  else
+    item_list.push_back(item_null, mem_root);
+
+  /* `ref` */
+  StringBuffer<64> ref_list_buf;
+  if (ref_list.is_empty())
+  {
+    if (type == JT_FT)
+    {
+      /* Traditionally, EXPLAIN lines with type=fulltext have ref='' */
+      push_str(thd, &item_list, "");
+    }
+    else
+      item_list.push_back(item_null, mem_root);
+  }
+  else
+    push_string_list(thd, &item_list, ref_list, &ref_list_buf);
+ 
+  /* `rows` */
+  StringBuffer<64> rows_str;
+  if (rows_set)
+  {
+    rows_str.append_ulonglong((ulonglong)rows);
+
+    if (rowid_filter)
+    {
+      rows_str.append(STRING_WITH_LEN(" ("));
+      rows_str.append_ulonglong((ulonglong) (round(rowid_filter->selectivity *
+						   100.0)));
+      rows_str.append(STRING_WITH_LEN("%)"));
+    }
+    item_list.push_back(new (mem_root)
+                        Item_string_sys(thd, rows_str.ptr(),
+                                        rows_str.length()), mem_root);
+  }
+  else
+    item_list.push_back(item_null, mem_root);
+
+  /* `r_rows` */
+  StringBuffer<64> r_rows_str;
+  if (is_analyze)
+  {
+    if (!tracker.has_scans())
+    {
+      item_list.push_back(item_null, mem_root);
+    }
+    else
+    {
+      double avg_rows= tracker.get_avg_rows();
+      Item_float *fl= new (mem_root) Item_float(thd, avg_rows, 2);
+      String tmp;
+      String *res= fl->val_str(&tmp);
+      r_rows_str.append(*res);
+      if (rowid_filter)
+      {
+        r_rows_str.append(STRING_WITH_LEN(" ("));
+        r_rows_str.append_ulonglong(
+	  (ulonglong) (rowid_filter->tracker->get_r_selectivity_pct() * 100.0));
+        r_rows_str.append(STRING_WITH_LEN("%)"));
+      }
+      item_list.push_back(new (mem_root)
+                          Item_string_sys(thd, r_rows_str.ptr(),
+                                          r_rows_str.length()), mem_root);
+    }
+  }
+
+  /* `filtered` */
+  if (explain_flags & DESCRIBE_EXTENDED || is_analyze)
+  {
+    if (filtered_set)
+    {
+      item_list.push_back(new (mem_root) Item_float(thd, filtered, 2),
+                          mem_root);
+    }
+    else
+      item_list.push_back(item_null, mem_root);
+  }
+
+  /* `r_filtered` */
+  if (is_analyze)
+  {
+    if (!tracker.has_scans())
+    {
+      item_list.push_back(item_null, mem_root);
+    }
+    else
+    {
+      double r_filtered= tracker.get_filtered_after_where();
+      if (bka_type.is_using_jbuf())
+        r_filtered *= jbuf_tracker.get_filtered_after_where();
+      item_list.push_back(new (mem_root)
+                          Item_float(thd, r_filtered * 100.0, 2),
+                          mem_root);
+    }
+  }
+
+  /* `Extra` */
+  StringBuffer<256> extra_buf;
+  bool first= true;
+  for (int i=0; i < (int)extra_tags.elements(); i++)
+  {
+    if (first)
+      first= false;
+    else
+      extra_buf.append(STRING_WITH_LEN("; "));
+    append_tag_name(&extra_buf, extra_tags.at(i));
+  }
+
+  if (using_temporary)
+  {
+    if (first)
+      first= false;
+    else
+      extra_buf.append(STRING_WITH_LEN("; "));
+    extra_buf.append(STRING_WITH_LEN("Using temporary"));
+  }
+
+  if (using_filesort || this->pre_join_sort)
+  {
+    if (first)
+      first= false;
+    else
+      extra_buf.append(STRING_WITH_LEN("; "));
+    extra_buf.append(STRING_WITH_LEN("Using filesort"));
+  }
+
+  if (rowid_filter)
+  {
+    if (first)
+      first= false;
+    else
+      extra_buf.append(STRING_WITH_LEN("; "));
+    extra_buf.append(STRING_WITH_LEN("Using rowid filter"));
+  }
+
+  item_list.push_back(new (mem_root)
+                      Item_string_sys(thd, extra_buf.ptr(),
+                                      extra_buf.length()),
+                      mem_root);
+
+  if (output->send_data(item_list))
+    return 1;
+
+  return 0;
+}
+
+
+/**
+  Adds copy of the string to the list
+
+  @param mem_root        where to allocate string
+  @param str             string to copy and add
+
+  @return
+    NULL - out of memory error
+    poiner on allocated copy of the string
+*/
+
+const char *String_list::append_str(MEM_ROOT *mem_root, const char *str)
+{
+  size_t len= strlen(str);
+  char *cp;
+  if (!(cp = (char*)alloc_root(mem_root, len+1)))
+    return NULL;
+  memcpy(cp, str, len+1);
+  push_back(cp, mem_root);
+  return cp;
+}
+
+
+static void write_item(Json_writer *writer, Item *item)
+{
+  THD *thd= current_thd;
+  char item_buf[256];
+  String str(item_buf, sizeof(item_buf), &my_charset_bin);
+  str.length(0);
+
+  ulonglong save_option_bits= thd->variables.option_bits;
+  thd->variables.option_bits &= ~OPTION_QUOTE_SHOW_CREATE;
+
+  item->print(&str, QT_EXPLAIN);
+
+  thd->variables.option_bits= save_option_bits;
+  writer->add_str(str.c_ptr_safe());
+}
+
+static void append_item_to_str(String *out, Item *item)
+{
+  THD *thd= current_thd;
+  ulonglong save_option_bits= thd->variables.option_bits;
+  thd->variables.option_bits &= ~OPTION_QUOTE_SHOW_CREATE;
+
+  item->print(out, QT_EXPLAIN);
+
+  thd->variables.option_bits= save_option_bits;
+}
+
+void Explain_table_access::tag_to_json(Json_writer *writer,
+                                       enum explain_extra_tag tag)
+{
+  switch (tag)
+  {
+    case ET_OPEN_FULL_TABLE:
+      writer->add_member("open_full_table").add_bool(true);
+      break;
+    case ET_SCANNED_0_DATABASES:
+      writer->add_member("scanned_databases").add_ll(0);
+      break;
+    case ET_SCANNED_1_DATABASE:
+      writer->add_member("scanned_databases").add_ll(1);
+      break;
+    case ET_SCANNED_ALL_DATABASES:
+      writer->add_member("scanned_databases").add_str("all");
+      break;
+    case ET_SKIP_OPEN_TABLE:
+      writer->add_member("skip_open_table").add_bool(true);
+      break;
+    case ET_OPEN_FRM_ONLY:
+      writer->add_member("open_frm_only").add_bool(true);
+      break;
+    case ET_USING_INDEX_CONDITION:
+      writer->add_member("index_condition");
+      write_item(writer, pushed_index_cond);
+      break;
+    case ET_USING_INDEX_CONDITION_BKA:
+      writer->add_member("index_condition_bka");
+      write_item(writer, pushed_index_cond);
+      break;
+    case ET_USING_WHERE:
+      {
+        /*
+          We are printing the condition that is checked when scanning this
+          table.
+          - when join buffer is used, it is cache_cond. 
+          - in other cases, it is where_cond.
+        */
+        Item *item= bka_type.is_using_jbuf()? cache_cond: where_cond;
+        if (item)
+        {
+          writer->add_member("attached_condition");
+          write_item(writer, item);
+        }
+      }
+      break;
+    case ET_USING_INDEX:
+      writer->add_member("using_index").add_bool(true);
+      break;
+    case ET_USING:
+      // index merge: case ET_USING 
+      break;
+    case ET_RANGE_CHECKED_FOR_EACH_RECORD:
+      /* Handled as range_checked_fer */
+    case ET_USING_JOIN_BUFFER:
+      /* Do nothing. Join buffer is handled differently */
+    case ET_START_TEMPORARY:
+    case ET_END_TEMPORARY:
+      /* Handled as "duplicates_removal: { ... } */
+    case ET_FULL_SCAN_ON_NULL_KEY:
+      /* Handled in full_scan_on_null_key */
+      break;
+    case ET_FIRST_MATCH:
+      writer->add_member("first_match").add_str(firstmatch_table_name.c_ptr());
+      break;
+    case ET_LOOSESCAN:
+      writer->add_member("loose_scan").add_bool(true);
+      break;
+    case ET_USING_MRR:
+      writer->add_member("mrr_type").add_str(mrr_type.c_ptr());
+      break;
+    case ET_USING_INDEX_FOR_GROUP_BY:
+      writer->add_member("using_index_for_group_by");
+      if (loose_scan_is_scanning)
+        writer->add_str("scanning");
+      else
+        writer->add_bool(true);
+      break;
+
+    /*new:*/
+    case ET_CONST_ROW_NOT_FOUND:
+      writer->add_member("const_row_not_found").add_bool(true);
+      break;
+    case ET_UNIQUE_ROW_NOT_FOUND:
+      /* 
+        Currently, we never get here.  All SELECTs that have 
+        ET_UNIQUE_ROW_NOT_FOUND for a table are converted into degenerate
+        SELECTs with message="Impossible WHERE ...". 
+        MySQL 5.6 has the same property.
+        I'm leaving the handling in just for the sake of covering all enum
+        members and safety.
+      */
+      writer->add_member("unique_row_not_found").add_bool(true);
+      break;
+    case ET_IMPOSSIBLE_ON_CONDITION:
+      writer->add_member("impossible_on_condition").add_bool(true);
+      break;
+    case ET_USING_WHERE_WITH_PUSHED_CONDITION:
+      /*
+        It would be nice to print the pushed condition, but current Storage
+        Engine API doesn't provide any way to do that
+      */
+      writer->add_member("pushed_condition").add_bool(true);
+      break;
+
+    case ET_NOT_EXISTS:
+      writer->add_member("not_exists").add_bool(true);
+      break;
+    case ET_DISTINCT:
+      writer->add_member("distinct").add_bool(true);
+      break;
+    case ET_TABLE_FUNCTION:
+      writer->add_member("table_function").add_str("json_table");
+      break;
+
+    default:
+      DBUG_ASSERT(0);
+  }
+}
+
+
+static
+void add_json_keyset(Json_writer *writer, const char *elem_name,
+                     String_list *keyset)
+{
+  if (!keyset->is_empty())
+    print_json_array(writer, elem_name, *keyset);
+}
+
+
+void Explain_rowid_filter::print_explain_json(Explain_query *query,
+                                              Json_writer *writer,
+                                              bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+  writer->add_member("rowid_filter").start_object();
+  quick->print_json(writer);
+  writer->add_member("rows").add_ll(rows);
+  writer->add_member("selectivity_pct").add_double(selectivity * 100.0);
+  if (is_analyze)
+  {
+    writer->add_member("r_rows").add_double(tracker->get_container_elements());
+    writer->add_member("r_lookups").add_ll(tracker->get_container_lookups());
+    writer->add_member("r_selectivity_pct").
+      add_double(tracker->get_r_selectivity_pct() * 100.0);
+    writer->add_member("r_buffer_size").
+      add_double((double) (tracker->get_container_buff_size()));
+    writer->add_member("r_filling_time_ms").
+      add_double(tracker->get_time_fill_container_ms());
+  }
+  writer->end_object(); // rowid_filter
+}
+
+static void trace_engine_stats(handler *file, Json_writer *writer)
+{
+  if (file && file->handler_stats)
+  {
+    ha_handler_stats *hs= file->handler_stats;
+    writer->add_member("r_engine_stats").start_object();
+    if (hs->pages_accessed)
+      writer->add_member("pages_accessed").add_ull(hs->pages_accessed);
+    if (hs->pages_updated)
+      writer->add_member("pages_updated").add_ull(hs->pages_updated);
+    if (hs->pages_read_count)
+      writer->add_member("pages_read_count").add_ull(hs->pages_read_count);
+    if (hs->pages_read_time)
+      writer->add_member("pages_read_time_ms").
+        add_double(hs->pages_read_time / 1000.0);
+    if (hs->undo_records_read)
+      writer->add_member("old_rows_read").add_ull(hs->undo_records_read);
+    writer->end_object();
+  }
+}
+
+void Explain_table_access::print_explain_json(Explain_query *query,
+                                              Json_writer *writer,
+                                              bool is_analyze)
+{
+  Json_writer_object jsobj(writer);
+  
+  if (pre_join_sort)
+  {
+    /* filesort was invoked on this join tab before doing the join with the rest */
+    writer->add_member("read_sorted_file").start_object();
+    if (is_analyze)
+    {
+      writer->add_member("r_rows");
+      /*
+        r_rows when reading filesort result. This can be less than the number
+        of rows produced by filesort due to NL-join having LIMIT.
+      */
+      if (tracker.has_scans())
+        writer->add_double(tracker.get_avg_rows());
+      else
+        writer->add_null();
+
+      /* 
+        r_filtered when reading filesort result. We should have checked the
+        WHERE while doing filesort but lets check just in case.
+      */
+      if (tracker.has_scans() && tracker.get_filtered_after_where() < 1.0)
+      {
+        writer->add_member("r_filtered");
+        writer->add_double(tracker.get_filtered_after_where()*100.0);
+      }
+    }
+    writer->add_member("filesort").start_object();
+    pre_join_sort->print_json_members(writer, is_analyze);
+  }
+
+  if (bka_type.is_using_jbuf())
+  {
+    writer->add_member("block-nl-join").start_object();
+  }
+
+  if (range_checked_fer)
+  {
+    range_checked_fer->print_json(writer, is_analyze);
+  }
+
+  if (full_scan_on_null_key)
+    writer->add_member("full-scan-on-null_key").start_object();
+
+  writer->add_member("table").start_object();
+
+  writer->add_member("table_name").add_str(table_name);
+
+  if (used_partitions_set)
+    print_json_array(writer, "partitions", used_partitions_list);
+
+  writer->add_member("access_type").add_str(join_type_str[type]);
+
+  add_json_keyset(writer, "possible_keys", &possible_keys);
+
+  /* `key` */
+  /* For non-basic quick select, 'key' will not be present */
+  if (!quick_info || quick_info->is_basic())
+  {
+    StringBuffer<64> key_str;
+    fill_key_str(&key_str, true);
+    if (key_str.length())
+      writer->add_member("key").add_str(key_str);
+  }
+
+  /* `key_length` */
+  StringBuffer<64> key_len_str;
+  fill_key_len_str(&key_len_str, true);
+  if (key_len_str.length())
+    writer->add_member("key_length").add_str(key_len_str);
+
+  /* `used_key_parts` */
+  String_list *parts_list= NULL;
+  if (quick_info && quick_info->is_basic())
+    parts_list= &quick_info->range.key_parts_list;
+  else
+    parts_list= &key.key_parts_list;
+
+  if (parts_list && !parts_list->is_empty())
+    print_json_array(writer, "used_key_parts", *parts_list);
+
+  if (quick_info && !quick_info->is_basic())
+  {
+    writer->add_member("index_merge").start_object();
+    quick_info->print_json(writer);
+    writer->end_object();
+  }
+  
+  /* `ref` */
+  if (!ref_list.is_empty())
+    print_json_array(writer, "ref", ref_list);
+
+  if (rowid_filter)
+  {
+    rowid_filter->print_explain_json(query, writer, is_analyze);
+  }
+
+  /* r_loops (not present in tabular output) */
+  if (is_analyze)
+  {
+    writer->add_member("r_loops").add_ll(tracker.get_loops());
+  }
+  
+  /* `rows` */
+  if (rows_set)
+    writer->add_member("rows").add_ull(rows);
+
+  /* `r_rows` */
+  if (is_analyze)
+  {
+    writer->add_member("r_rows");
+    if (pre_join_sort)
+    {
+      /* Get r_rows value from filesort */
+      if (pre_join_sort->tracker.get_r_loops())
+        writer->add_double(pre_join_sort->tracker.get_avg_examined_rows());
+      else
+        writer->add_null();
+    }
+    else
+    {
+      if (tracker.has_scans())
+        writer->add_double(tracker.get_avg_rows());
+      else
+        writer->add_null();
+    }
+
+    if (op_tracker.get_loops())
+    {
+      double total_time= op_tracker.get_time_ms();
+      if (rowid_filter)
+        total_time+= rowid_filter->tracker->get_time_fill_container_ms();
+      writer->add_member("r_table_time_ms").add_double(total_time);
+      writer->add_member("r_other_time_ms").add_double(extra_time_tracker.get_time_ms());
+    }
+    trace_engine_stats(handler_for_stats, writer);
+  }
+
+  /* `filtered` */
+  if (filtered_set)
+    writer->add_member("filtered").add_double(filtered);
+
+  /* `r_filtered` */
+  if (is_analyze)
+  {
+    writer->add_member("r_filtered");
+    if (pre_join_sort)
+    {
+      /* Get r_filtered value from filesort */
+      if (pre_join_sort->tracker.get_r_loops())
+        writer->add_double(pre_join_sort->tracker.get_r_filtered()*100);
+      else
+        writer->add_null();
+    }
+    else
+    {
+      /* Get r_filtered from the NL-join runtime */
+      if (tracker.has_scans())
+        writer->add_double(tracker.get_filtered_after_where()*100.0);
+      else
+        writer->add_null();
+    }
+  }
+
+  for (int i=0; i < (int)extra_tags.elements(); i++)
+  {
+    tag_to_json(writer, extra_tags.at(i));
+  }
+  
+  if (full_scan_on_null_key)
+    writer->end_object(); //"full-scan-on-null_key"
+
+  if (range_checked_fer)
+    writer->end_object(); // "range-checked-for-each-record"
+
+  if (bka_type.is_using_jbuf())
+  {
+    writer->end_object(); // "block-nl-join"
+    writer->add_member("buffer_type").add_str(bka_type.incremental?
+                                              "incremental":"flat");
+    writer->add_member("buffer_size").add_size(bka_type.join_buffer_size);
+    writer->add_member("join_type").add_str(bka_type.join_alg);
+    if (bka_type.mrr_type.length())
+      writer->add_member("mrr_type").add_str(bka_type.mrr_type);
+    if (where_cond)
+    {
+      writer->add_member("attached_condition");
+      write_item(writer, where_cond);
+    }
+
+    if (is_analyze)
+    {
+      writer->add_member("r_loops").add_ll(jbuf_loops_tracker.get_loops());
+
+      writer->add_member("r_filtered");
+      if (jbuf_tracker.has_scans())
+        writer->add_double(jbuf_tracker.get_filtered_after_where()*100.0);
+      else
+        writer->add_null();
+
+      writer->add_member("r_unpack_time_ms");
+      writer->add_double(jbuf_unpack_tracker.get_time_ms());
+      DBUG_EXECUTE_IF("analyze_print_r_unpack_ops",
+                      {
+                        writer->add_member("r_unpack_ops");
+                        writer->add_ull(jbuf_unpack_tracker.get_loops());
+                      });
+
+      writer->add_member("r_other_time_ms").
+        add_double(jbuf_extra_time_tracker.get_time_ms());
+      /*
+        effective_rows is average number of matches we got for an incoming
+        row. The row is stored in the join buffer and then is read
+        from there, possibly multiple times. We can't count this number
+        directly. Infer it as:
+         total_number_of_row_combinations_considered / r_loops.
+      */
+      writer->add_member("r_effective_rows");
+      if (jbuf_loops_tracker.has_scans())
+      {
+        double loops= (double)jbuf_loops_tracker.get_loops();
+        double row_combinations= (double)jbuf_tracker.r_rows;
+        writer->add_double(row_combinations / loops);
+      }
+      else
+        writer->add_null();
+    }
+  }
+
+  if (derived_select_number)
+  {
+    /* This is a derived table. Print its contents here */
+    writer->add_member("materialized").start_object();
+    Explain_node *node= query->get_node(derived_select_number);
+    if (node->get_type() == Explain_node::EXPLAIN_SELECT &&
+        ((Explain_select*)node)->is_lateral)
+    {
+      writer->add_member("lateral").add_ll(1);
+    }
+    node->print_explain_json(query, writer, is_analyze);
+    writer->end_object();
+  }
+  if (non_merged_sjm_number)
+  {
+    /* This is a non-merged semi-join table. Print its contents here */
+    writer->add_member("materialized").start_object();
+    writer->add_member("unique").add_ll(1);
+    Explain_node *node= query->get_node(non_merged_sjm_number);
+    node->connection_type= Explain_node::EXPLAIN_NODE_NON_MERGED_SJ;
+    node->print_explain_json(query, writer, is_analyze);
+    writer->end_object();
+  }
+  if (sjm_nest)
+  {
+    /* This is a non-merged semi-join table. Print its contents here */
+    writer->add_member("materialized").start_object();
+    writer->add_member("unique").add_ll(1);
+    sjm_nest->print_explain_json(query, writer, is_analyze);
+    writer->end_object();
+  }
+
+  if (pre_join_sort)
+  {
+    writer->end_object(); // filesort
+    writer->end_object(); // read_sorted_file
+  }
+
+  writer->end_object();
+}
+
+
+/*
+  Elements in this array match members of enum explain_extra_tag, defined in
+  sql_explain.h
+*/
+
+const LEX_CSTRING extra_tag_text[]=
+{
+  { STRING_WITH_LEN("ET_none") },
+  { STRING_WITH_LEN("Using index condition") },
+  { STRING_WITH_LEN("Using index condition(BKA)") },
+  { STRING_WITH_LEN("Using ") }, // special handling
+  { STRING_WITH_LEN("Range checked for each record (index map: 0x") },  // special handling
+  { STRING_WITH_LEN("Using where with pushed condition") },
+  { STRING_WITH_LEN("Using where") },
+  { STRING_WITH_LEN("Not exists") },
+  
+  { STRING_WITH_LEN("Using index") },
+  { STRING_WITH_LEN("Full scan on NULL key") },
+  { STRING_WITH_LEN("Skip_open_table") },
+  { STRING_WITH_LEN("Open_frm_only") },
+  { STRING_WITH_LEN("Open_full_table") },
+
+  { STRING_WITH_LEN("Scanned 0 databases") },
+  { STRING_WITH_LEN("Scanned 1 database") },
+  { STRING_WITH_LEN("Scanned all databases") },
+
+  { STRING_WITH_LEN("Using index for group-by") }, // special handling
+  { STRING_WITH_LEN("USING MRR: DONT PRINT ME") }, // special handling
+
+  { STRING_WITH_LEN("Distinct") },
+  { STRING_WITH_LEN("LooseScan") },
+  { STRING_WITH_LEN("Start temporary") },
+  { STRING_WITH_LEN("End temporary") },
+  { STRING_WITH_LEN("FirstMatch") },               // special handling
+
+  { STRING_WITH_LEN("Using join buffer") },        // special handling
+
+  { STRING_WITH_LEN("Const row not found") },
+  { STRING_WITH_LEN("Unique row not found") },
+  { STRING_WITH_LEN("Impossible ON condition") }
+};
+
+
+void Explain_table_access::append_tag_name(String *str, enum explain_extra_tag tag)
+{
+  switch (tag) {
+    case ET_USING:
+    {
+      // quick select
+      str->append(STRING_WITH_LEN("Using "));
+      quick_info->print_extra(str);
+      break;
+    }
+    case ET_RANGE_CHECKED_FOR_EACH_RECORD:
+    {
+      /* 4 bits per 1 hex digit + terminating '\0' */
+      char buf[MAX_KEY / 4 + 1];
+      str->append(STRING_WITH_LEN("Range checked for each "
+                                   "record (index map: 0x"));
+      range_checked_fer->keys_map.print(buf);
+      str->append(buf, strlen(buf));
+      str->append(')');
+      break;
+    }
+    case ET_USING_MRR:
+    {
+      str->append(mrr_type);
+      break;
+    }
+    case ET_USING_JOIN_BUFFER:
+    {
+      str->append(extra_tag_text[tag]);
+
+      str->append(STRING_WITH_LEN(" ("));
+      LEX_CSTRING buffer_type;
+      if (bka_type.incremental)
+        buffer_type= { STRING_WITH_LEN("incremental") };
+      else
+        buffer_type= { STRING_WITH_LEN("flat") };
+      str->append(buffer_type);
+      str->append(STRING_WITH_LEN(", "));
+      str->append(bka_type.join_alg, strlen(bka_type.join_alg));
+      str->append(STRING_WITH_LEN(" join"));
+      str->append(')');
+      if (bka_type.mrr_type.length())
+      {
+        str->append(STRING_WITH_LEN("; "));
+        str->append(bka_type.mrr_type);
+      }
+
+      break;
+    }
+    case ET_FIRST_MATCH:
+    {
+      if (firstmatch_table_name.length())
+      {
+        str->append(STRING_WITH_LEN("FirstMatch("));
+        str->append(firstmatch_table_name);
+        str->append(')');
+      }
+      else
+        str->append(extra_tag_text[tag]);
+      break;
+    }
+    case ET_USING_INDEX_FOR_GROUP_BY:
+    {
+      str->append(extra_tag_text[tag]);
+      if (loose_scan_is_scanning)
+        str->append(STRING_WITH_LEN(" (scanning)"));
+      break;
+    case ET_TABLE_FUNCTION:
+      str->append(STRING_WITH_LEN("Table function: json_table"));
+      break;
+    }
+    default:
+     str->append(extra_tag_text[tag]);
+  }
+}
+
+
+/* 
+  This is called for top-level Explain_quick_select only. The point of this
+  function is:
+  - index_merge should print $index_merge_type (child, ...)
+  - 'range'  should not print anything.
+*/
+
+void Explain_quick_select::print_extra(String *str)
+{
+  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
+      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC ||
+      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+  {
+    /* print nothing */
+  }
+  else
+    print_extra_recursive(str);
+}
+
+void Explain_quick_select::print_json(Json_writer *writer)
+{
+  if (is_basic())
+  {
+    writer->add_member("range").start_object();
+
+    writer->add_member("key").add_str(range.get_key_name());
+
+    print_json_array(writer, "used_key_parts", range.key_parts_list);
+
+    writer->end_object();
+  }
+  else
+  {
+    Json_writer_array ranges(writer, get_name_by_type());
+
+    List_iterator_fast<Explain_quick_select> it (children);
+    Explain_quick_select* child;
+    while ((child = it++))
+    {
+      Json_writer_object obj(writer);
+      child->print_json(writer);
+    }
+  }
+}
+
+void Explain_quick_select::print_extra_recursive(String *str)
+{
+  const char *name;
+  if (is_basic())
+  {
+    name= range.get_key_name();
+    str->append(name, strlen(name));
+  }
+  else
+  {
+    name= get_name_by_type();
+    str->append(name, strlen(name));
+    str->append('(');
+    List_iterator_fast<Explain_quick_select> it (children);
+    Explain_quick_select* child;
+    bool first= true;
+    while ((child = it++))
+    {
+      if (first)
+        first= false;
+      else
+        str->append(',');
+
+      child->print_extra_recursive(str);
+    }
+    str->append(')');
+  }
+}
+
+
+const char * Explain_quick_select::get_name_by_type()
+{
+  switch (quick_type) {
+    case QUICK_SELECT_I::QS_TYPE_INDEX_MERGE:
+      return "sort_union";
+    case QUICK_SELECT_I::QS_TYPE_ROR_UNION:
+      return "union";
+    case QUICK_SELECT_I::QS_TYPE_ROR_INTERSECT:
+      return "intersect";
+    case QUICK_SELECT_I::QS_TYPE_INDEX_INTERSECT:
+      return "sort_intersect";
+    default:
+      DBUG_ASSERT(0);
+      return "unknown quick select type";
+  }
+}
+
+
+/*
+  This prints a comma-separated list of used indexes, ignoring nesting
+*/
+
+void Explain_quick_select::print_key(String *str)
+{
+  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
+      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC || 
+      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+  {
+    if (str->length() > 0)
+      str->append(',');
+    str->append(range.get_key_name(), strlen(range.get_key_name()));
+  }
+  else
+  {
+    List_iterator_fast<Explain_quick_select> it (children);
+    Explain_quick_select* child;
+    while ((child = it++))
+    {
+      child->print_key(str);
+    }
+  }
+}
+
+
+/*
+  This prints a comma-separated list of used key_lengths, ignoring nesting
+*/
+
+void Explain_quick_select::print_key_len(String *str)
+{
+  if (quick_type == QUICK_SELECT_I::QS_TYPE_RANGE || 
+      quick_type == QUICK_SELECT_I::QS_TYPE_RANGE_DESC ||
+      quick_type == QUICK_SELECT_I::QS_TYPE_GROUP_MIN_MAX)
+  {
+    char buf[64];
+    size_t length;
+    length= longlong10_to_str(range.get_key_len(), buf, 10) - buf;
+    if (str->length() > 0)
+      str->append(',');
+    str->append(buf, length);
+  }
+  else
+  {
+    List_iterator_fast<Explain_quick_select> it (children);
+    Explain_quick_select* child;
+    while ((child = it++))
+    {
+      child->print_key_len(str);
+    }
+  }
+}
+
+
+int Explain_delete::print_explain(Explain_query *query, 
+                                  select_result_sink *output,
+                                  uint8 explain_flags,
+                                  bool is_analyze)
+{
+  if (deleting_all_rows)
+  {
+    const char *msg= STR_DELETING_ALL_ROWS;
+    int res= print_explain_message_line(output, explain_flags, is_analyze,
+                                        1 /*select number*/,
+                                        select_type, &rows, msg);
+    return res;
+
+  }
+  else
+  {
+    return Explain_update::print_explain(query, output, explain_flags,
+                                         is_analyze);
+  }
+}
+
+
+void Explain_delete::print_explain_json(Explain_query *query, 
+                                        Json_writer *writer,
+                                        bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+
+  if (deleting_all_rows)
+  {
+    writer->add_member("query_block").start_object();
+    writer->add_member("select_id").add_ll(1);
+    writer->add_member("table").start_object();
+    // just like mysql-5.6, we don't print table name. Is this ok?
+    writer->add_member("message").add_str(STR_DELETING_ALL_ROWS);
+    writer->end_object(); // table
+    writer->end_object(); // query_block
+    return;
+  }
+  Explain_update::print_explain_json(query, writer, is_analyze);
+}
+
+
+int Explain_update::print_explain(Explain_query *query, 
+                                  select_result_sink *output,
+                                  uint8 explain_flags,
+                                  bool is_analyze)
+{
+  StringBuffer<64> key_buf;
+  StringBuffer<64> key_len_buf;
+  StringBuffer<64> extra_str;
+  if (impossible_where || no_partitions)
+  {
+    const char *msg= impossible_where ? 
+                     STR_IMPOSSIBLE_WHERE : 
+                     STR_NO_ROWS_AFTER_PRUNING;
+    int res= print_explain_message_line(output, explain_flags, is_analyze,
+                                        1 /*select number*/,
+                                        select_type, 
+                                        NULL, /* rows */
+                                        msg);
+    return res;
+  }
+
+  if (quick_info)
+  {
+    quick_info->print_key(&key_buf);
+    quick_info->print_key_len(&key_len_buf);
+
+    StringBuffer<64> quick_buf;
+    quick_info->print_extra(&quick_buf);
+    if (quick_buf.length())
+    {
+      extra_str.append(STRING_WITH_LEN("Using "));
+      extra_str.append(quick_buf);
+    }
+  }
+  else if (key.get_key_name())
+  {
+    const char *name= key.get_key_name();
+    key_buf.set(name, strlen(name), &my_charset_bin);
+    char buf[64];
+    size_t length= longlong10_to_str(key.get_key_len(), buf, 10) - buf;
+    key_len_buf.copy(buf, length, &my_charset_bin);
+  }
+
+  if (using_where)
+  {
+    if (extra_str.length() !=0)
+      extra_str.append(STRING_WITH_LEN("; "));
+    extra_str.append(STRING_WITH_LEN("Using where"));
+  }
+
+  if (mrr_type.length() != 0)
+  {
+    if (extra_str.length() !=0)
+      extra_str.append(STRING_WITH_LEN("; "));
+    extra_str.append(mrr_type);
+  }
+  
+  if (is_using_filesort())
+  {
+    if (extra_str.length() !=0)
+      extra_str.append(STRING_WITH_LEN("; "));
+    extra_str.append(STRING_WITH_LEN("Using filesort"));
+  }
+
+  if (using_io_buffer)
+  {
+    if (extra_str.length() !=0)
+      extra_str.append(STRING_WITH_LEN("; "));
+    extra_str.append(STRING_WITH_LEN("Using buffer"));
+  }
+
+  /* 
+    Single-table DELETE commands do not do "Using temporary".
+    "Using index condition" is also not possible (which is an unjustified limitation)
+  */
+  double r_filtered= 100 * tracker.get_filtered_after_where();
+  double r_rows= tracker.get_avg_rows();
+
+  print_explain_row(output, explain_flags, is_analyze,
+                    1, /* id */
+                    select_type,
+                    table_name.c_ptr(), 
+                    used_partitions_set? used_partitions.c_ptr() : NULL,
+                    jtype,
+                    &possible_keys,
+                    key_buf.length()? key_buf.c_ptr() : NULL,
+                    key_len_buf.length() ? key_len_buf.c_ptr() : NULL,
+                    NULL, /* 'ref' is always NULL in single-table EXPLAIN DELETE */
+                    &rows,
+                    tracker.has_scans()? &r_rows : NULL,
+                    r_filtered,
+                    extra_str.c_ptr_safe());
+
+  return print_explain_for_children(query, output, explain_flags, is_analyze);
+}
+
+
+void Explain_update::print_explain_json(Explain_query *query,
+                                        Json_writer *writer,
+                                        bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+
+  writer->add_member("query_block").start_object();
+  writer->add_member("select_id").add_ll(1);
+ 
+  /* This is the total time it took to do the UPDATE/DELETE */
+  if (is_analyze && command_tracker.has_timed_statistics())
+  {
+    writer->add_member("r_total_time_ms").
+            add_double(command_tracker.get_time_ms());
+  }
+  
+  if (impossible_where || no_partitions)
+  {
+    const char *msg= impossible_where ?  STR_IMPOSSIBLE_WHERE : 
+                                         STR_NO_ROWS_AFTER_PRUNING;
+    writer->add_member("table").start_object();
+    writer->add_member("message").add_str(msg);
+    writer->end_object(); // table
+    writer->end_object(); // query_block
+    return;
+  }
+
+  DBUG_ASSERT(!(is_using_filesort() && using_io_buffer));
+  
+  bool doing_buffering= false;
+
+  if (is_using_filesort())
+  {
+    writer->add_member("filesort").start_object();
+    if (is_analyze)
+      filesort_tracker->print_json_members(writer);
+    doing_buffering= true;
+  }
+
+  if (using_io_buffer)
+  {
+    writer->add_member("buffer").start_object();
+    doing_buffering= true;
+  }
+
+  /* Produce elements that are common for buffered and un-buffered cases */
+  writer->add_member("table").start_object();
+
+  if (get_type() == EXPLAIN_UPDATE)
+    writer->add_member("update").add_ll(1);
+  else
+    writer->add_member("delete").add_ll(1);
+
+  writer->add_member("table_name").add_str(table_name);
+
+  if (used_partitions_set)
+    print_json_array(writer, "partitions", used_partitions_list);
+
+  writer->add_member("access_type").add_str(join_type_str[jtype]);
+
+  if (!possible_keys.is_empty())
+  {
+    List_iterator_fast<char> it(possible_keys);
+    const char *name;
+    writer->add_member("possible_keys").start_array();
+    while ((name= it++))
+      writer->add_str(name);
+    writer->end_array();
+  }
+
+  /* `key`, `key_length` */
+  if (quick_info && quick_info->is_basic())
+  {
+    StringBuffer<64> key_buf;
+    StringBuffer<64> key_len_buf;
+    quick_info->print_extra_recursive(&key_buf);
+    quick_info->print_key_len(&key_len_buf);
+    
+    writer->add_member("key").add_str(key_buf);
+    writer->add_member("key_length").add_str(key_len_buf);
+  }
+  else if (key.get_key_name())
+  {
+    writer->add_member("key").add_str(key.get_key_name());
+    writer->add_member("key_length").add_str(key.get_key_len());
+  }
+
+  /* `used_key_parts` */
+  String_list *parts_list= NULL;
+  if (quick_info && quick_info->is_basic())
+    parts_list= &quick_info->range.key_parts_list;
+  else
+    parts_list= &key.key_parts_list;
+
+  if (parts_list && !parts_list->is_empty())
+  {
+    List_iterator_fast<char> it(*parts_list);
+    const char *name;
+    writer->add_member("used_key_parts").start_array();
+    while ((name= it++))
+      writer->add_str(name);
+    writer->end_array();
+  }
+
+  if (quick_info && !quick_info->is_basic())
+  {
+    writer->add_member("index_merge").start_object();
+    quick_info->print_json(writer);
+    writer->end_object();
+  }
+  
+  /* `rows` */
+  writer->add_member("rows").add_ull(rows);
+
+
+  if (mrr_type.length() != 0)
+    writer->add_member("mrr_type").add_str(mrr_type.ptr());
+
+  if (is_analyze)
+  {
+    if (doing_buffering)
+    {
+      ha_rows r_rows;
+      double r_filtered;
+
+      if (is_using_filesort())
+      {
+        if (filesort_tracker->get_r_loops())
+          r_rows= (ha_rows) filesort_tracker->get_avg_examined_rows();
+        else
+          r_rows= 0;
+        r_filtered= filesort_tracker->get_r_filtered() * 100.0;
+      }
+      else
+      {
+        if (buf_tracker.has_scans())
+          r_rows= (ha_rows) buf_tracker.get_avg_rows();
+        else
+          r_rows= 0;
+        r_filtered= buf_tracker.get_filtered_after_where() * 100.0;
+      }
+      writer->add_member("r_rows").add_ull(r_rows);
+      writer->add_member("r_filtered").add_double(r_filtered);
+    }
+    else /* Not doing buffering */
+    {
+      writer->add_member("r_rows");
+      if (tracker.has_scans())
+        writer->add_double(tracker.get_avg_rows());
+      else
+        writer->add_null();
+
+      /* There is no 'filtered' estimate in UPDATE/DELETE atm */
+      double r_filtered= tracker.get_filtered_after_where() * 100.0;
+      writer->add_member("r_filtered").add_double(r_filtered);
+    }
+
+    if (table_tracker.has_timed_statistics())
+    {
+      writer->add_member("r_total_time_ms").
+              add_double(table_tracker.get_time_ms());
+    }
+  }
+
+  trace_engine_stats(handler_for_stats, writer);
+
+  if (where_cond)
+  {
+    writer->add_member("attached_condition");
+    write_item(writer, where_cond);
+  }
+
+  /*** The part of plan that is before the buffering/sorting ends here ***/
+  if (is_using_filesort())
+    writer->end_object();
+
+  if (using_io_buffer)
+    writer->end_object();
+
+  writer->end_object(); // table
+
+  print_explain_json_for_children(query, writer, is_analyze);
+  writer->end_object(); // query_block
+}
+
+
+int Explain_insert::print_explain(Explain_query *query, 
+                                  select_result_sink *output, 
+                                  uint8 explain_flags,
+                                  bool is_analyze)
+{
+  const char *select_type="INSERT";
+  print_explain_row(output, explain_flags, is_analyze,
+                    1, /* id */
+                    select_type,
+                    table_name.c_ptr(), 
+                    NULL, // partitions
+                    JT_ALL,
+                    NULL, // possible_keys
+                    NULL, // key
+                    NULL, // key_len
+                    NULL, // ref
+                    NULL, // rows
+                    NULL, // r_rows
+                    100.0, // r_filtered
+                    NULL);
+
+  return print_explain_for_children(query, output, explain_flags, is_analyze);
+}
+
+void Explain_insert::print_explain_json(Explain_query *query, 
+                                        Json_writer *writer, bool is_analyze)
+{
+  Json_writer_nesting_guard guard(writer);
+
+  writer->add_member("query_block").start_object();
+  writer->add_member("select_id").add_ll(1);
+  writer->add_member("table").start_object();
+  writer->add_member("table_name").add_str(table_name.c_ptr());
+  writer->end_object(); // table
+  print_explain_json_for_children(query, writer, is_analyze);
+  writer->end_object(); // query_block
+}
+
+
+void delete_explain_query(LEX *lex)
+{
+  DBUG_ENTER("delete_explain_query");
+  delete lex->explain;
+  lex->explain= NULL;
+  DBUG_VOID_RETURN;
+}
+
+
+void create_explain_query(LEX *lex, MEM_ROOT *mem_root)
+{
+  DBUG_ASSERT(!lex->explain);
+  DBUG_ENTER("create_explain_query");
+
+  lex->explain= new (mem_root) Explain_query(lex->thd, mem_root);
+  DBUG_ASSERT(mem_root == current_thd->mem_root);
+
+  DBUG_VOID_RETURN;
+}
+
+void create_explain_query_if_not_exists(LEX *lex, MEM_ROOT *mem_root)
+{
+  if (!lex->explain)
+    create_explain_query(lex, mem_root);
+}
+
+
+/**
+  Build arrays for collectiong keys statistics, sdd possible key names
+  to the list and name array
+
+  @param alloc           MEM_ROOT to put data in
+  @param list            list of possible key names to fill
+  @param table           table of the keys
+  @patam possible_keys   possible keys map
+
+  @retval 0 - OK
+  @retval 1 - Error
+*/
+
+int Explain_range_checked_fer::append_possible_keys_stat(MEM_ROOT *alloc,
+                                                         TABLE *table,
+                                                         key_map possible_keys)
+{
+  uint j;
+  multi_alloc_root(alloc, &keys_stat, sizeof(ha_rows) * table->s->keys,
+                   &keys_stat_names, sizeof(char *) * table->s->keys, NULL);
+  if ((!keys_stat) || (!keys_stat_names))
+  {
+    keys_stat= NULL;
+    keys_stat_names= NULL;
+    return 1;
+  }
+  keys_map= possible_keys;
+  keys= table->s->keys;
+  bzero(keys_stat, sizeof(ha_rows) * table->s->keys);
+  for (j= 0; j < table->s->keys; j++)
+  {
+    if (possible_keys.is_set(j))
+    {
+      if (!(keys_stat_names[j]= key_set.append_str(alloc,
+                                                   table->key_info[j].name.str)))
+        return 1;
+    }
+    else
+      keys_stat_names[j]= NULL;
+  }
+  return 0;
+}
+
+void Explain_range_checked_fer::collect_data(QUICK_SELECT_I *quick)
+{
+  if (quick)
+  {
+    if (quick->index == MAX_KEY)
+      index_merge++;
+    else
+    {
+      DBUG_ASSERT(quick->index < keys);
+      DBUG_ASSERT(keys_stat);
+      DBUG_ASSERT(keys_stat_names);
+      DBUG_ASSERT(keys_stat_names[ quick->index]);
+      keys_stat[quick->index]++;
+    }
+  }
+  else
+    full_scan++;
+}
+
+
+void Explain_range_checked_fer::print_json(Json_writer *writer,
+                                           bool is_analyze)
+{
+  writer->add_member("range-checked-for-each-record").start_object();
+  add_json_keyset(writer, "keys", &key_set);
+  if (is_analyze)
+  {
+    writer->add_member("r_keys").start_object();
+    writer->add_member("full_scan").add_ll(full_scan);
+    writer->add_member("index_merge").add_ll(index_merge);
+    if (keys_stat)
+    {
+      writer->add_member("range").start_object();
+      for (uint i= 0; i < keys; i++)
+      {
+        if (keys_stat_names[i])
+        {
+          writer->add_member(keys_stat_names[i]).add_ll(keys_stat[i]);
+        }
+      }
+      writer->end_object();
+    }
+    writer->end_object();
+  }
+}