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, 1455 insertions, 0 deletions

diff --git a/sql/sql_join_cache.h b/sql/sql_join_cache.h
new file mode 100644
index 00000000..d2d2e1a1
--- /dev/null
+++ b/sql/sql_join_cache.h
@@ -0,0 +1,1455 @@
+/*
+   Copyright (c) 2011, 2012, 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 */
+
+/*
+  This file contains declarations for implementations
+  of block based join algorithms
+*/
+
+#define JOIN_CACHE_INCREMENTAL_BIT           1
+#define JOIN_CACHE_HASHED_BIT                2
+#define JOIN_CACHE_BKA_BIT                   4
+
+/* 
+  Categories of data fields of variable length written into join cache buffers.
+  The value of any of these fields is written into cache together with the
+  prepended length of the value.     
+*/
+#define CACHE_BLOB      1        /* blob field  */
+#define CACHE_STRIPPED  2        /* field stripped of trailing spaces */
+#define CACHE_VARSTR1   3        /* short string value (length takes 1 byte) */ 
+#define CACHE_VARSTR2   4        /* long string value (length takes 2 bytes) */
+#define CACHE_ROWID     5        /* ROWID field */
+
+/*
+  The CACHE_FIELD structure used to describe fields of records that
+  are written into a join cache buffer from record buffers and backward.
+*/
+typedef struct st_cache_field {
+  uchar *str;   /**< buffer from/to where the field is to be copied */ 
+  uint length;  /**< maximal number of bytes to be copied from/to str */
+  /* 
+    Field object for the moved field
+    (0 - for a flag field, see JOIN_CACHE::create_flag_fields).
+  */
+  Field *field;
+  uint type;    /**< category of the of the copied field (CACHE_BLOB et al.) */
+  /* 
+    The number of the record offset value for the field in the sequence
+    of offsets placed after the last field of the record. These
+    offset values are used to access fields referred to from other caches.
+    If the value is 0 then no offset for the field is saved in the
+    trailing sequence of offsets.
+  */ 
+  uint referenced_field_no; 
+  /* The remaining structure fields are used as containers for temp values */
+  uint blob_length; /**< length of the blob to be copied */
+  uint offset;      /**< field offset to be saved in cache buffer */
+} CACHE_FIELD;
+
+
+class JOIN_TAB_SCAN;
+
+class EXPLAIN_BKA_TYPE;
+
+/*
+  JOIN_CACHE is the base class to support the implementations of 
+  - Block Nested Loop (BNL) Join Algorithm,
+  - Block Nested Loop Hash (BNLH) Join Algorithm,
+  - Batched Key Access (BKA) Join Algorithm.
+
+  The first algorithm is supported by the derived class JOIN_CACHE_BNL,
+  the second algorithm is supported by the derived class JOIN_CACHE_BNLH,
+  while the third algorithm is implemented in two variant supported by
+  the classes JOIN_CACHE_BKA and JOIN_CACHE_BKAH.
+  These three algorithms have a lot in common. Each of them first accumulates
+  the records of the left join operand in a join buffer and then searches for
+  matching rows of the second operand for all accumulated records.
+  For the first two algorithms this strategy saves on logical I/O operations:
+  the entire set of records from the join buffer requires only one look-through
+  of the records provided by the second operand. 
+  For the third algorithm the accumulation of records allows to optimize
+  fetching rows of the second operand from disk for some engines (MyISAM, 
+  InnoDB), or to minimize the number of round-trips between the Server and
+  the engine nodes.        
+*/ 
+
+class JOIN_CACHE :public Sql_alloc
+{
+
+private:
+
+  /* Size of the offset of a record from the cache */   
+  uint size_of_rec_ofs;    
+  /* Size of the length of a record in the cache */
+  uint size_of_rec_len;
+  /* Size of the offset of a field within a record in the cache */   
+  uint size_of_fld_ofs;
+
+  /* This structure is used only for explain, not for execution */
+  bool for_explain_only;
+
+protected:
+       
+  /* 3 functions below actually do not use the hidden parameter 'this' */ 
+
+  /* Calculate the number of bytes used to store an offset value */
+  uint offset_size(size_t len)
+  { return (len < 256 ? 1 : len < 256*256 ? 2 : 4); }
+
+  /* Get the offset value that takes ofs_sz bytes at the position ptr */
+  ulong get_offset(uint ofs_sz, uchar *ptr)
+  {
+    switch (ofs_sz) {
+    case 1: return uint(*ptr);
+    case 2: return uint2korr(ptr);
+    case 4: return uint4korr(ptr);
+    }
+    return 0;
+  }
+
+  /* Set the offset value ofs that takes ofs_sz bytes at the position ptr */ 
+  void store_offset(uint ofs_sz, uchar *ptr, ulong ofs)
+  {
+    switch (ofs_sz) {
+    case 1: *ptr= (uchar) ofs; return;
+    case 2: int2store(ptr, (uint16) ofs); return;
+    case 4: int4store(ptr, (uint32) ofs); return;
+    }
+  }
+  size_t calc_avg_record_length();
+  
+  /* 
+    The maximum total length of the fields stored for a record in the cache.
+    For blob fields only the sizes of the blob lengths are taken into account. 
+  */
+  uint length;
+
+  /* 
+    Representation of the executed multi-way join through which all needed
+    context can be accessed.  
+  */   
+  JOIN *join;  
+
+  /*
+    JOIN_TAB of the first table that can have it's fields in the join cache. 
+    That is, tables in the [start_tab, tab) range can have their fields in the
+    join cache. 
+    If a join tab in the range represents an SJM-nest, then all tables from the
+    nest can have their fields in the join cache, too.
+  */
+  JOIN_TAB *start_tab;
+
+  /* 
+    The total number of flag and data fields that can appear in a record
+    written into the cache. Fields with null values are always skipped 
+    to save space. 
+  */
+  uint fields;
+
+  /* 
+    The total number of flag fields in a record put into the cache. They are
+    used for table null bitmaps, table null row flags, and an optional match
+    flag. Flag fields go before other fields in a cache record with the match
+    flag field placed always at the very beginning of the record.
+  */
+  uint flag_fields;
+
+  /* The total number of blob fields that are written into the cache */ 
+  uint blobs;
+
+  /* 
+    The total number of fields referenced from field descriptors for other join
+    caches. These fields are used to construct key values.
+    When BKA join algorithm is employed the constructed key values serve to
+    access matching rows with index lookups.
+    The key values are put into a hash table when the BNLH join algorithm
+    is employed and when BKAH is used for the join operation. 
+  */   
+  uint referenced_fields;
+   
+  /* 
+    The current number of already created data field descriptors.
+    This number can be useful for implementations of the init methods.  
+  */
+  uint data_field_count; 
+
+  /* 
+    The current number of already created pointers to the data field
+    descriptors. This number can be useful for implementations of
+    the init methods.  
+  */
+  uint data_field_ptr_count;
+ 
+  /* 
+    Array of the descriptors of fields containing 'fields' elements.
+    These are all fields that are stored for a record in the cache. 
+  */
+  CACHE_FIELD *field_descr;
+
+  /* 
+    Array of pointers to the blob descriptors that contains 'blobs' elements.
+  */
+  CACHE_FIELD **blob_ptr;
+
+  /* 
+    This flag indicates that records written into the join buffer contain
+    a match flag field.
+    This is set to true for the first inner table of an outer join or a
+    semi-join.
+    The flag must be set by the init method.
+    Currently any implementation of the virtial init method calls
+    the function JOIN_CACHE::calc_record_fields() to set this flag.
+  */
+  bool with_match_flag;
+  /*
+    This flag indicates that any record is prepended with the length of the
+    record which allows us to skip the record or part of it without reading.
+  */
+  bool with_length;
+
+  /* 
+    The maximal number of bytes used for a record representation in
+    the cache excluding the space for blob data. 
+    For future derived classes this representation may contains some
+    redundant info such as a key value associated with the record.     
+  */
+  uint pack_length;
+  /* 
+    The value of pack_length incremented by the total size of all 
+    pointers of a record in the cache to the blob data. 
+  */
+  uint pack_length_with_blob_ptrs;
+
+  /* 
+    The total size of the record base prefix. The base prefix of record may
+    include the following components:
+     - the length of the record
+     - the link to a record in a previous buffer.
+    Each record in the buffer are supplied with the same set of the components.
+  */
+  uint base_prefix_length;
+
+  /*
+    The expected length of a record in the join buffer together with     
+    all prefixes and postfixes
+  */
+  size_t avg_record_length;
+
+  /* The expected size of the space per record in the auxiliary buffer */
+  size_t avg_aux_buffer_incr;
+
+  /* Pointer to the beginning of the join buffer */
+  uchar *buff;         
+  /* 
+    Size of the entire memory allocated for the join buffer.
+    Part of this memory may be reserved for the auxiliary buffer.
+  */ 
+  size_t buff_size;
+  /* The minimal join buffer size when join buffer still makes sense to use */
+  size_t min_buff_size;
+  /* The maximum expected size if the join buffer to be used */
+  size_t max_buff_size;
+  /* Size of the auxiliary buffer */ 
+  size_t aux_buff_size;
+
+  /* The number of records put into the join buffer */ 
+  size_t records;
+  /* 
+    The number of records in the fully refilled join buffer of
+    the minimal size equal to min_buff_size
+  */
+  size_t min_records;
+
+  /* 
+    Pointer to the current position in the join buffer.
+    This member is used both when writing to buffer and
+    when reading from it.
+  */
+  uchar *pos;
+  /* 
+    Pointer to the first free position in the join buffer,
+    right after the last record into it.
+  */
+  uchar *end_pos; 
+
+  /* 
+    Pointer to the beginning of the first field of the current read/write
+    record from the join buffer. The value is adjusted by the 
+    get_record/put_record functions.
+  */
+  uchar *curr_rec_pos;
+  /* 
+    Pointer to the beginning of the first field of the last record
+    from the join buffer.
+  */
+  uchar *last_rec_pos;
+
+  /* 
+    Flag is set if the blob data for the last record in the join buffer
+    is in record buffers rather than in the join cache.
+  */
+  bool last_rec_blob_data_is_in_rec_buff;
+
+  /* 
+    Pointer to the position to the current record link. 
+    Record links are used only with linked caches. Record links allow to set
+    connections between parts of one join record that are stored in different
+    join buffers.
+    In the simplest case a record link is just a pointer to the beginning of
+    the record stored in the buffer.
+    In a more general case a link could be a reference to an array of pointers
+    to records in the buffer.
+  */
+  uchar *curr_rec_link;
+
+  /* 
+    This flag is set to TRUE if join_tab is the first inner table of an outer
+    join and  the latest record written to the join buffer is detected to be
+    null complemented after checking on conditions over the outer tables for
+    this outer join operation
+  */ 
+  bool last_written_is_null_compl;
+
+  /*
+    The number of fields put in the join buffer of the join cache that are
+    used in building keys to access the table join_tab
+  */
+  uint local_key_arg_fields;
+  /* 
+    The total number of the fields in the previous caches that are used
+    in building keys to access the table join_tab
+  */
+  uint external_key_arg_fields;
+
+  /* 
+    This flag indicates that the key values will be read directly from the join
+    buffer. It will save us building key values in the key buffer.
+  */
+  bool use_emb_key;
+  /* The length of an embedded key value */ 
+  uint emb_key_length;
+
+  /* This flag is used only when 'not exists' optimization can be applied */
+  bool not_exists_opt_is_applicable;
+
+  /*
+    This object provides the methods to iterate over records of
+    the joined table join_tab when looking for join matches between
+    records from join buffer and records from join_tab.
+    BNL and BNLH join algorithms retrieve all records from join_tab,
+    while BKA/BKAH algorithm iterates only over those records from
+    join_tab that can be accessed by look-ups with join keys built
+    from records in join buffer.  
+  */
+  JOIN_TAB_SCAN *join_tab_scan;
+
+  void calc_record_fields();     
+  void collect_info_on_key_args();
+  int alloc_fields();
+  void create_flag_fields();
+  void create_key_arg_fields();
+  void create_remaining_fields();
+  void set_constants();
+  int alloc_buffer();
+
+  /* Shall reallocate the join buffer */
+  virtual int realloc_buffer();
+  
+  /* Check the possibility to read the access keys directly from join buffer */ 
+  bool check_emb_key_usage();
+
+  uint get_size_of_rec_offset() { return size_of_rec_ofs; }
+  uint get_size_of_rec_length() { return size_of_rec_len; }
+  uint get_size_of_fld_offset() { return size_of_fld_ofs; }
+
+  uchar *get_rec_ref(uchar *ptr)
+  {
+    return buff+get_offset(size_of_rec_ofs, ptr-size_of_rec_ofs);
+  }
+  ulong get_rec_length(uchar *ptr)
+  { 
+    return (ulong) get_offset(size_of_rec_len, ptr);
+  }
+  ulong get_fld_offset(uchar *ptr)
+  { 
+    return (ulong) get_offset(size_of_fld_ofs, ptr);
+  }
+
+  void store_rec_ref(uchar *ptr, uchar* ref)
+  {
+    store_offset(size_of_rec_ofs, ptr-size_of_rec_ofs, (ulong) (ref-buff));
+  }
+  void store_rec_length(uchar *ptr, ulong len)
+  {
+    store_offset(size_of_rec_len, ptr, len);
+  }
+  void store_fld_offset(uchar *ptr, ulong ofs)
+  {
+    store_offset(size_of_fld_ofs, ptr, ofs);
+  }
+
+  /* Write record fields and their required offsets into the join buffer */ 
+  uint write_record_data(uchar *link, bool *is_full);
+
+  /* Get the total length of all prefixes of a record in the join buffer */ 
+  virtual uint get_prefix_length() { return base_prefix_length; }
+  /* Get maximum total length of all affixes of a record in the join buffer */
+  virtual uint get_record_max_affix_length(); 
+
+  /* 
+    Shall get maximum size of the additional space per record used for
+    record keys
+  */
+  virtual uint get_max_key_addon_space_per_record() { return 0; }
+
+  /* 
+    This method must determine for how much the auxiliary buffer should be
+    incremented when a new record is added to the join buffer.
+    If no auxiliary buffer is needed the function should return 0.
+  */
+  virtual uint aux_buffer_incr(size_t recno);
+
+  /* Shall calculate how much space is remaining in the join buffer */ 
+  virtual size_t rem_space() 
+  { 
+    return MY_MAX(buff_size-(end_pos-buff)-aux_buff_size,0);
+  }
+
+  /* 
+    Shall calculate how much space is taken by allocation of the key
+    for a record in the join buffer
+  */
+  virtual uint extra_key_length() { return 0; }
+
+  /*  Read all flag and data fields of a record from the join buffer */
+  uint read_all_record_fields();
+  
+  /* Read all flag fields of a record from the join buffer */
+  uint read_flag_fields();
+
+  /* Read a data record field from the join buffer */
+  uint read_record_field(CACHE_FIELD *copy, bool last_record);
+
+  /* Read a referenced field from the join buffer */
+  bool read_referenced_field(CACHE_FIELD *copy, uchar *rec_ptr, uint *len);
+
+  /* 
+    Shall skip record from the join buffer if its match flag
+    is set to MATCH_FOUND
+ */
+  virtual bool skip_if_matched();
+
+  /* 
+    Shall skip record from the join buffer if its match flag
+    commands to do so
+  */
+  virtual bool skip_if_not_needed_match();
+
+  /* 
+    True if rec_ptr points to the record whose blob data stay in
+    record buffers
+  */
+  bool blob_data_is_in_rec_buff(uchar *rec_ptr)
+  {
+    return rec_ptr == last_rec_pos && last_rec_blob_data_is_in_rec_buff;
+  }
+
+  /* Find matches from the next table for records from the join buffer */
+  virtual enum_nested_loop_state join_matching_records(bool skip_last);
+
+  /* Shall set an auxiliary buffer up (currently used only by BKA joins) */
+  virtual int setup_aux_buffer(HANDLER_BUFFER &aux_buff) 
+  {
+    DBUG_ASSERT(0);
+    return 0;
+  }
+
+  /*
+    Shall get the number of ranges in the cache buffer passed
+    to the MRR interface
+  */  
+  virtual uint get_number_of_ranges_for_mrr() { return 0; };
+
+  /* 
+    Shall prepare to look for records from the join cache buffer that would
+    match the record of the joined table read into the record buffer
+  */ 
+  virtual bool prepare_look_for_matches(bool skip_last)= 0;
+  /* 
+    Shall return a pointer to the record from join buffer that is checked
+    as the next candidate for a match with the current record from join_tab.
+    Each implementation of this virtual function should bare in mind
+    that the record position it returns shall be exactly the position
+    passed as the parameter to the implementations of the virtual functions 
+    skip_next_candidate_for_match and read_next_candidate_for_match.
+  */   
+  virtual uchar *get_next_candidate_for_match()= 0;
+  /*
+    Shall check whether the given record from the join buffer has its match
+    flag settings commands to skip the record in the buffer.
+  */
+  virtual bool skip_next_candidate_for_match(uchar *rec_ptr)= 0;
+  /*
+    Shall read the given record from the join buffer into the
+    the corresponding record buffer
+  */
+  virtual void read_next_candidate_for_match(uchar *rec_ptr)= 0;
+
+  /* 
+    Shall return the location of the association label returned by 
+    the multi_read_range_next function for the current record loaded
+    into join_tab's record buffer
+  */
+  virtual uchar **get_curr_association_ptr() { return 0; };
+
+  /* Add null complements for unmatched outer records from the join buffer */
+  virtual enum_nested_loop_state join_null_complements(bool skip_last);
+
+  /* Restore the fields of the last record from the join buffer */
+  virtual void restore_last_record();
+
+  /* Set match flag for a record in join buffer if it has not been set yet */
+  bool set_match_flag_if_none(JOIN_TAB *first_inner, uchar *rec_ptr);
+
+  enum_nested_loop_state generate_full_extensions(uchar *rec_ptr);
+
+  /* Check matching to a partial join record from the join buffer */
+  bool check_match(uchar *rec_ptr);
+
+  /* 
+    This constructor creates an unlinked join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+  */   
+  JOIN_CACHE(JOIN *j, JOIN_TAB *tab)
+  {
+    join= j;
+    join_tab= tab;
+    prev_cache= next_cache= 0;
+    buff= 0;
+    min_buff_size= max_buff_size= 0;            // Caches
+    not_exists_opt_is_applicable= false;
+  }
+
+  /* 
+    This constructor creates a linked join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+  */   
+  JOIN_CACHE(JOIN *j, JOIN_TAB *tab, JOIN_CACHE *prev)   
+  {  
+    join= j;
+    join_tab= tab;
+    next_cache= 0;
+    prev_cache= prev;
+    buff= 0;
+    min_buff_size= max_buff_size= 0;            // Caches
+    if (prev)
+      prev->next_cache= this;
+  }
+
+public:
+ 
+  /*
+    The enumeration type Join_algorithm includes a mnemonic constant for
+    each join algorithm that employs join buffers
+  */
+
+  enum Join_algorithm
+  { 
+    BNL_JOIN_ALG,     /* Block Nested Loop Join algorithm                  */
+    BNLH_JOIN_ALG,    /* Block Nested Loop Hash Join algorithm             */
+    BKA_JOIN_ALG,     /* Batched Key Access Join algorithm                 */
+    BKAH_JOIN_ALG    /* Batched Key Access with Hash Table Join Algorithm */
+  };
+
+  /* 
+    The enumeration type Match_flag describes possible states of the match flag
+    field  stored for the records of the first inner tables of outer joins and
+    semi-joins in the cases when the first match strategy is used for them.
+    When a record with match flag field is written into the join buffer the
+    state of the field usually is MATCH_NOT_FOUND unless this is a record of the
+    first inner table of the outer join for which the on precondition (the
+    condition from on expression over outer tables)  has turned out not to be 
+    true. In the last case the state of the match flag is MATCH_IMPOSSIBLE.
+    The state of the match flag field is changed to MATCH_FOUND as soon as
+    the first full matching combination of inner tables of the outer join or
+    the semi-join is discovered. 
+  */
+  enum Match_flag { MATCH_NOT_FOUND, MATCH_FOUND, MATCH_IMPOSSIBLE };
+
+  /* Table to be joined with the partial join records from the cache */ 
+  JOIN_TAB *join_tab;
+
+  /* Pointer to the previous join cache if there is any */
+  JOIN_CACHE *prev_cache;
+  /* Pointer to the next join cache if there is any */
+  JOIN_CACHE *next_cache;
+
+  /* Shall initialize the join cache structure */ 
+  virtual int init(bool for_explain);
+
+  /* Get the current size of the cache join buffer */ 
+  size_t get_join_buffer_size() { return buff_size; }
+  /* Set the size of the cache join buffer to a new value */
+  void set_join_buffer_size(size_t sz) { buff_size= sz; }
+
+  /* Get the minimum possible size of the cache join buffer */
+  size_t get_min_join_buffer_size();
+  /* Get the maximum possible size of the cache join buffer */ 
+  size_t get_max_join_buffer_size(bool optimize_buff_size,
+                                  size_t min_buffer_size_arg);
+
+  /* Shrink the size if the cache join buffer in a given ratio */
+  bool shrink_join_buffer_in_ratio(ulonglong n, ulonglong d);
+
+  /*  Shall return the type of the employed join algorithm */
+  virtual enum Join_algorithm get_join_alg()= 0;
+
+  /* 
+    The function shall return TRUE only when there is a key access
+    to the join table
+  */
+  virtual bool is_key_access()= 0;
+
+  /* Shall reset the join buffer for reading/writing */
+  virtual void reset(bool for_writing);
+
+  /* 
+    This function shall add a record into the join buffer and return TRUE
+    if it has been decided that it should be the last record in the buffer.
+  */ 
+  virtual bool put_record();
+
+  /* 
+    This function shall read the next record into the join buffer and return
+    TRUE if there is no more next records.
+  */ 
+  virtual bool get_record();
+
+  /* 
+    This function shall read the record at the position rec_ptr
+    in the join buffer
+  */ 
+  virtual void get_record_by_pos(uchar *rec_ptr);
+
+  /* Shall return the value of the match flag for the positioned record */
+  virtual enum Match_flag get_match_flag_by_pos(uchar *rec_ptr);
+
+  /*
+    Shall return the value of the match flag for the positioned record
+    from the join buffer attached to the specified table
+  */
+  virtual enum Match_flag
+    get_match_flag_by_pos_from_join_buffer(uchar *rec_ptr, JOIN_TAB *tab);
+
+  /* Shall return the position of the current record */
+  virtual uchar *get_curr_rec() { return curr_rec_pos; }
+
+  /* Shall set the current record link */
+  virtual void set_curr_rec_link(uchar *link) { curr_rec_link= link; }
+
+  /* Shall return the current record link */
+  virtual uchar *get_curr_rec_link()
+  { 
+    return (curr_rec_link ? curr_rec_link : get_curr_rec());
+  }
+     
+  /* Join records from the join buffer with records from the next join table */ 
+  enum_nested_loop_state join_records(bool skip_last);
+
+  /* Add a comment on the join algorithm employed by the join cache */
+  virtual bool save_explain_data(EXPLAIN_BKA_TYPE *explain);
+
+  THD *thd();
+
+  virtual ~JOIN_CACHE() = default;
+  void reset_join(JOIN *j) { join= j; }
+  void free()
+  { 
+    my_free(buff);
+    buff= 0;
+  }   
+  
+  friend class JOIN_CACHE_HASHED;
+  friend class JOIN_CACHE_BNL;
+  friend class JOIN_CACHE_BKA;
+  friend class JOIN_TAB_SCAN;
+  friend class JOIN_TAB_SCAN_MRR;
+
+};
+
+
+/*
+  The class JOIN_CACHE_HASHED is the base class for the classes
+  JOIN_CACHE_HASHED_BNL and JOIN_CACHE_HASHED_BKA. The first of them supports
+  an implementation of Block Nested Loop Hash (BNLH) Join Algorithm,
+  while the second is used for a variant of the BKA Join algorithm that performs
+  only one lookup for any records from join buffer with the same key value. 
+  For a join cache of this class the records from the join buffer that have
+  the same access key are linked into a chain attached to a key entry structure
+  that either itself contains the key value, or, in the case when the keys are
+  embedded, refers to its occurrence in one of the records from the chain.
+  To build the chains with the same keys a hash table is employed. It is placed
+  at the very end of the join buffer. The array of hash entries is allocated
+  first at the very bottom of the join buffer, while key entries are placed
+  before this array.
+  A hash entry contains a header of the list of the key entries with the same
+  hash value. 
+  Each key entry is a structure of the following type:
+    struct st_join_cache_key_entry {
+      union { 
+        uchar[] value;
+        cache_ref *value_ref; // offset from the beginning of the buffer
+      } hash_table_key;
+      key_ref next_key; // offset backward from the beginning of hash table
+      cache_ref *last_rec // offset from the beginning of the buffer
+    }
+  The references linking the records in a chain are always placed at the very
+  beginning of the record info stored in the join buffer. The records are 
+  linked in a circular list. A new record is always added to the end of this 
+  list.
+
+  The following picture represents a typical layout for the info stored in the
+  join buffer of a join cache object of the JOIN_CACHE_HASHED class.
+    
+  buff
+  V
+  +----------------------------------------------------------------------------+
+  |     |[*]record_1_1|                                                        |
+  |     ^ |                                                                    |
+  |     | +--------------------------------------------------+                 |
+  |     |                           |[*]record_2_1|          |                 |
+  |     |                           ^ |                      V                 |
+  |     |                           | +------------------+   |[*]record_1_2|   |
+  |     |                           +--------------------+-+   |               |
+  |+--+ +---------------------+                          | |   +-------------+ |
+  ||  |                       |                          V |                 | |
+  |||[*]record_3_1|         |[*]record_1_3|              |[*]record_2_2|     | |
+  ||^                       ^                            ^                   | |
+  ||+----------+            |                            |                   | |
+  ||^          |            |<---------------------------+-------------------+ |
+  |++          | | ... mrr  |   buffer ...           ... |     |               |
+  |            |            |                            |                     |
+  |      +-----+--------+   |                      +-----|-------+             |
+  |      V     |        |   |                      V     |       |             |
+  ||key_3|[/]|[*]|      |   |                |key_2|[/]|[*]|     |             |
+  |                   +-+---|-----------------------+            |             |
+  |                   V |   |                       |            |             |
+  |             |key_1|[*]|[*]|         |   | ... |[*]|   ...  |[*]|  ...  |   |
+  +----------------------------------------------------------------------------+
+                                        ^           ^            ^
+                                        |           i-th entry   j-th entry
+                                        hash table
+
+  i-th hash entry:
+    circular record chain for key_1:
+      record_1_1
+      record_1_2
+      record_1_3 (points to record_1_1)
+    circular record chain for key_3:
+      record_3_1 (points to itself)
+
+  j-th hash entry:
+    circular record chain for key_2:
+      record_2_1
+      record_2_2 (points to record_2_1)
+
+*/
+
+class JOIN_CACHE_HASHED: public JOIN_CACHE
+{
+
+  typedef uint (JOIN_CACHE_HASHED::*Hash_func) (uchar *key, uint key_len);
+  typedef bool (JOIN_CACHE_HASHED::*Hash_cmp_func) (uchar *key1, uchar *key2,
+                                                    uint key_len);
+  
+private:
+
+  /* Size of the offset of a key entry in the hash table */
+  uint size_of_key_ofs;
+
+  /* 
+    Length of the key entry in the hash table.
+    A key entry either contains the key value, or it contains a reference
+    to the key value if use_emb_key flag is set for the cache.
+  */ 
+  uint key_entry_length;
+ 
+  /* The beginning of the hash table in the join buffer */
+  uchar *hash_table;
+  /* Number of hash entries in the hash table */
+  uint hash_entries;
+
+
+  /* The position of the currently retrieved key entry in the hash table */
+  uchar *curr_key_entry;
+
+  /* The offset of the data fields from the beginning of the record fields */
+  uint data_fields_offset;
+
+  inline uint get_hash_idx_simple(uchar *key, uint key_len);
+  inline uint get_hash_idx_complex(uchar *key, uint key_len);
+
+  inline bool equal_keys_simple(uchar *key1, uchar *key2, uint key_len);
+  inline bool equal_keys_complex(uchar *key1, uchar *key2, uint key_len);
+
+  int init_hash_table();
+  void cleanup_hash_table();
+  
+protected:
+
+  /* 
+    Index info on the TABLE_REF object used by the hash join
+    to look for matching records
+  */    
+  KEY *ref_key_info;
+  /* 
+    Number of the key parts the TABLE_REF object used by the hash join
+    to look for matching records
+  */    
+  uint ref_used_key_parts;
+
+  /*
+    The hash function used in the hash table,
+    usually set by the init() method
+  */ 
+  Hash_func hash_func;
+  /*
+    The function to check whether two key entries in the hash table
+    are equal or not, usually set by the init() method
+  */ 
+  Hash_cmp_func hash_cmp_func;
+
+  /* 
+    Length of a key value.
+    It is assumed that all key values have the same length.
+  */
+  uint key_length;
+  /* Buffer to store key values for probing */
+  uchar *key_buff;
+
+  /* Number of key entries in the hash table (number of distinct keys) */
+  uint key_entries;
+
+  /* The position of the last key entry in the hash table */
+  uchar *last_key_entry;
+
+  /* 
+    The offset of the record fields from the beginning of the record
+    representation. The record representation starts with a reference to
+    the next record in the key record chain followed by the length of
+    the trailing record data followed by a reference to the record segment
+    in the previous cache, if any, followed by the record fields.
+  */ 
+  uint rec_fields_offset;
+
+  uint get_size_of_key_offset() { return size_of_key_ofs; }
+
+  /* 
+    Get the position of the next_key_ptr field pointed to by 
+    a linking reference stored at the position key_ref_ptr. 
+    This reference is actually the offset backward from the
+    beginning of hash table.
+  */  
+  uchar *get_next_key_ref(uchar *key_ref_ptr)
+  {
+    return hash_table-get_offset(size_of_key_ofs, key_ref_ptr);
+  }
+
+  /* 
+    Store the linking reference to the next_key_ptr field at 
+    the position key_ref_ptr. The position of the next_key_ptr
+    field is pointed to by ref. The stored reference is actually
+    the offset backward from the beginning of the hash table.
+  */  
+  void store_next_key_ref(uchar *key_ref_ptr, uchar *ref)
+  {
+    store_offset(size_of_key_ofs, key_ref_ptr, (ulong) (hash_table-ref));
+  }     
+  
+  /* 
+    Check whether the reference to the next_key_ptr field at the position
+    key_ref_ptr contains  a nil value.
+  */
+  bool is_null_key_ref(uchar *key_ref_ptr)
+  {
+    ulong nil= 0;
+    return memcmp(key_ref_ptr, &nil, size_of_key_ofs ) == 0;
+  } 
+
+  /* 
+    Set the reference to the next_key_ptr field at the position
+    key_ref_ptr equal to nil.
+  */
+  void store_null_key_ref(uchar *key_ref_ptr)
+  {
+    ulong nil= 0;
+    store_offset(size_of_key_ofs, key_ref_ptr, nil);
+  } 
+
+  uchar *get_next_rec_ref(uchar *ref_ptr)
+  {
+    return buff+get_offset(get_size_of_rec_offset(), ref_ptr);
+  }
+
+  void store_next_rec_ref(uchar *ref_ptr, uchar *ref)
+  {
+    store_offset(get_size_of_rec_offset(), ref_ptr, (ulong) (ref-buff));
+  } 
+
+  /*
+    Get the position of the embedded key value for the current
+    record pointed to by get_curr_rec().
+  */ 
+  uchar *get_curr_emb_key()
+  {
+    return get_curr_rec()+data_fields_offset;
+  }
+
+  /*
+    Get the position of the embedded key value pointed to by a reference
+    stored at ref_ptr. The stored reference is actually the offset from
+    the beginning of the join buffer.
+  */  
+  uchar *get_emb_key(uchar *ref_ptr)
+  {
+    return buff+get_offset(get_size_of_rec_offset(), ref_ptr);
+  }
+
+  /* 
+    Store the reference to an embedded key at the position key_ref_ptr.
+    The position of the embedded key is pointed to by ref. The stored
+    reference is actually the offset from the beginning of the join buffer.
+  */  
+  void store_emb_key_ref(uchar *ref_ptr, uchar *ref)
+  {
+    store_offset(get_size_of_rec_offset(), ref_ptr, (ulong) (ref-buff));
+  }
+  
+  /* Get the total length of all prefixes of a record in hashed join buffer */ 
+  uint get_prefix_length() 
+  { 
+    return base_prefix_length + get_size_of_rec_offset();
+  }
+
+  /* 
+    Get maximum size of the additional space per record used for
+    the hash table with record keys
+  */
+  uint get_max_key_addon_space_per_record();
+
+  /* 
+    Calculate how much space in the buffer would not be occupied by
+    records, key entries and additional memory for the MMR buffer.
+  */ 
+  size_t rem_space() 
+  { 
+    return MY_MAX(last_key_entry-end_pos-aux_buff_size,0);
+  }
+
+  /* 
+    Calculate how much space is taken by allocation of the key
+    entry for a record in the join buffer
+  */
+  uint extra_key_length() { return key_entry_length; }
+
+  /* 
+    Skip record from a hashed join buffer if its match flag
+    is set to MATCH_FOUND
+  */
+  bool skip_if_matched();
+
+  /*
+    Skip record from a hashed join buffer if its match flag setting 
+    commands to do so
+  */
+  bool skip_if_not_needed_match();
+
+  /* Search for a key in the hash table of the join buffer */
+  bool key_search(uchar *key, uint key_len, uchar **key_ref_ptr);
+
+  /* Reallocate the join buffer of a hashed join cache */
+  int realloc_buffer();
+
+  /* 
+    This constructor creates an unlinked hashed join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+  */   
+  JOIN_CACHE_HASHED(JOIN *j, JOIN_TAB *tab) :JOIN_CACHE(j, tab) {}
+
+  /* 
+    This constructor creates a linked hashed join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+  */   
+  JOIN_CACHE_HASHED(JOIN *j, JOIN_TAB *tab, JOIN_CACHE *prev) 
+		    :JOIN_CACHE(j, tab, prev) {}
+
+public:
+
+  /* Initialize a hashed join cache */       
+  int init(bool for_explain);
+
+  /* Reset the buffer of a hashed join cache for reading/writing */
+  void reset(bool for_writing);
+
+  /* Add a record into the buffer of a hashed join cache */
+  bool put_record();
+
+  /* Read the next record from the buffer of a hashed join cache */
+  bool get_record();
+
+  /*
+    Shall check whether all records in a key chain have 
+    their match flags set on
+  */   
+  virtual bool check_all_match_flags_for_key(uchar *key_chain_ptr);
+
+  uint get_next_key(uchar **key); 
+  
+  /* Get the head of the record chain attached to the current key entry */ 
+  uchar *get_curr_key_chain()
+  {
+    return get_next_rec_ref(curr_key_entry+key_entry_length-
+                            get_size_of_rec_offset());
+  }
+  
+};
+
+
+/*
+  The class JOIN_TAB_SCAN is a companion class for the classes JOIN_CACHE_BNL
+  and JOIN_CACHE_BNLH. Actually the class implements the iterator over the
+  table joinded by BNL/BNLH join algorithm.
+  The virtual functions open, next and close are called for any iteration over
+  the table. The function open is called to initiate the process of the 
+  iteration. The function next shall read the next record from the joined
+  table. The record is read into the record buffer of the joined table.
+  The record is to be matched with records from the join cache buffer. 
+  The function close shall perform the finalizing actions for the iteration.
+*/
+   
+class JOIN_TAB_SCAN: public Sql_alloc
+{
+
+private:
+  /* TRUE if this is the first record from the joined table to iterate over */
+  bool is_first_record;
+
+protected:
+
+  /* The joined table to be iterated over */
+  JOIN_TAB *join_tab;
+  /* The join cache used to join the table join_tab */ 
+  JOIN_CACHE *cache;
+  /* 
+    Representation of the executed multi-way join through which
+    all needed context can be accessed.  
+  */   
+  JOIN *join;
+
+public:
+  
+  JOIN_TAB_SCAN(JOIN *j, JOIN_TAB *tab)
+  {
+    join= j;
+    join_tab= tab;
+    cache= join_tab->cache;
+  }
+
+  virtual ~JOIN_TAB_SCAN() = default;
+ 
+  /* 
+    Shall calculate the increment of the auxiliary buffer for a record
+    write if such a buffer is used by the table scan object 
+  */
+  virtual uint aux_buffer_incr(size_t recno) { return 0; }
+
+  /* Initiate the process of iteration over the joined table */
+  virtual int open();
+  /* 
+    Shall read the next candidate for matches with records from 
+    the join buffer.
+  */
+  virtual int next();
+  /* 
+    Perform the finalizing actions for the process of iteration
+    over the joined_table.
+  */ 
+  virtual void close();
+
+};
+
+/*
+  The class JOIN_CACHE_BNL is used when the BNL join algorithm is
+  employed to perform a join operation   
+*/
+
+class JOIN_CACHE_BNL :public JOIN_CACHE
+{
+private:
+  /* 
+    The number of the records in the join buffer that have to be
+    checked yet for a match with the current record of join_tab 
+    read into the record buffer.
+  */
+  uint rem_records;
+
+protected:
+
+  bool prepare_look_for_matches(bool skip_last);
+
+  uchar *get_next_candidate_for_match();
+
+  bool skip_next_candidate_for_match(uchar *rec_ptr);
+
+  void read_next_candidate_for_match(uchar *rec_ptr);
+
+public:
+
+  /* 
+    This constructor creates an unlinked BNL join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+  */   
+  JOIN_CACHE_BNL(JOIN *j, JOIN_TAB *tab) :JOIN_CACHE(j, tab) {}
+
+  /* 
+    This constructor creates a linked BNL join cache. The cache is to be 
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+  */   
+  JOIN_CACHE_BNL(JOIN *j, JOIN_TAB *tab, JOIN_CACHE *prev) 
+    :JOIN_CACHE(j, tab, prev) {}
+
+  /* Initialize the BNL cache */       
+  int init(bool for_explain);
+
+  enum Join_algorithm get_join_alg() { return BNL_JOIN_ALG; }
+
+  bool is_key_access() { return FALSE; }
+
+};
+
+
+/*
+  The class JOIN_CACHE_BNLH is used when the BNLH join algorithm is
+  employed to perform a join operation   
+*/
+
+class JOIN_CACHE_BNLH :public JOIN_CACHE_HASHED
+{
+
+protected:
+
+  /* 
+    The pointer to the last record from the circular list of the records
+    that  match the join key built out of the record in the join buffer for
+    the join_tab table
+  */
+  uchar *last_matching_rec_ref_ptr;
+  /*
+    The pointer to the next current  record from the circular list of the
+    records that match the join key built out of the record in the join buffer
+    for the join_tab table. This pointer is used by the class method 
+    get_next_candidate_for_match to iterate over records from the circular
+    list.
+  */
+  uchar *next_matching_rec_ref_ptr;
+
+  /*
+    Get the chain of records from buffer matching the current candidate
+    record for join
+  */
+  uchar *get_matching_chain_by_join_key();
+
+  bool prepare_look_for_matches(bool skip_last);
+
+  uchar *get_next_candidate_for_match();
+
+  bool skip_next_candidate_for_match(uchar *rec_ptr);
+
+  void read_next_candidate_for_match(uchar *rec_ptr);
+
+public:
+
+  /* 
+    This constructor creates an unlinked BNLH join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+  */   
+  JOIN_CACHE_BNLH(JOIN *j, JOIN_TAB *tab) : JOIN_CACHE_HASHED(j, tab) {}
+
+  /* 
+    This constructor creates a linked BNLH join cache. The cache is to be 
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+  */   
+  JOIN_CACHE_BNLH(JOIN *j, JOIN_TAB *tab, JOIN_CACHE *prev) 
+    : JOIN_CACHE_HASHED(j, tab, prev) {}
+
+  /* Initialize the BNLH cache */       
+  int init(bool for_explain);
+
+  enum Join_algorithm get_join_alg() { return BNLH_JOIN_ALG; }
+
+  bool is_key_access() { return TRUE; }
+
+};
+
+
+/*
+  The class JOIN_TAB_SCAN_MRR is a companion class for the classes
+  JOIN_CACHE_BKA and JOIN_CACHE_BKAH. Actually the class implements the
+  iterator over the records from join_tab selected by BKA/BKAH join
+  algorithm as the candidates to be joined. 
+  The virtual functions open, next and close are called for any iteration over
+  join_tab record candidates. The function open is called to initiate the
+  process of the iteration. The function next shall read the next record from
+  the set of the record candidates. The record is read into the record buffer
+  of the joined table. The function close shall perform the finalizing actions
+  for the iteration.
+*/
+   
+class JOIN_TAB_SCAN_MRR: public JOIN_TAB_SCAN
+{
+  /* Interface object to generate key ranges for MRR */
+  RANGE_SEQ_IF range_seq_funcs;
+
+  /* Number of ranges to be processed by the MRR interface */
+  uint ranges;
+
+  /* Flag to to be passed to the MRR interface */ 
+  uint mrr_mode;
+
+  /* MRR buffer assotiated with this join cache */
+  HANDLER_BUFFER mrr_buff;
+
+  /* Shall initialize the MRR buffer */
+  virtual void init_mrr_buff()
+  {
+    cache->setup_aux_buffer(mrr_buff);
+  }
+
+public:
+
+  JOIN_TAB_SCAN_MRR(JOIN *j, JOIN_TAB *tab, uint flags, RANGE_SEQ_IF rs_funcs)
+    :JOIN_TAB_SCAN(j, tab), range_seq_funcs(rs_funcs), mrr_mode(flags) {}
+
+  uint aux_buffer_incr(size_t recno);
+
+  int open();
+ 
+  int next();
+
+  friend class JOIN_CACHE_BKA; /* it needs to add an mrr_mode flag after JOIN_CACHE::init() call */
+};
+
+/*
+  The class JOIN_CACHE_BKA is used when the BKA join algorithm is
+  employed to perform a join operation   
+*/
+
+class JOIN_CACHE_BKA :public JOIN_CACHE
+{
+private:
+
+  /* Flag to to be passed to the companion JOIN_TAB_SCAN_MRR object */
+  uint mrr_mode;
+
+  /* 
+    This value is set to 1 by the class prepare_look_for_matches method
+    and back to 0 by the class get_next_candidate_for_match method
+  */
+  uint rem_records;
+
+  /*
+    This field contains the current association label set by a call of
+    the multi_range_read_next handler function.
+    See the function JOIN_CACHE_BKA::get_curr_key_association()
+  */
+  uchar *curr_association;
+
+protected:
+
+  /* 
+    Get the number of ranges in the cache buffer passed to the MRR
+    interface. For each record its own range is passed.
+  */
+  uint get_number_of_ranges_for_mrr() { return (uint)records; }
+
+ /*
+   Setup the MRR buffer as the space between the last record put
+   into the join buffer and the very end of the join buffer 
+ */
+  int setup_aux_buffer(HANDLER_BUFFER &aux_buff)
+  {
+    aux_buff.buffer= end_pos;
+    aux_buff.buffer_end= buff+buff_size;
+    return 0;
+  }
+
+  bool prepare_look_for_matches(bool skip_last);
+
+  uchar *get_next_candidate_for_match();
+
+  bool skip_next_candidate_for_match(uchar *rec_ptr);
+
+  void read_next_candidate_for_match(uchar *rec_ptr);
+
+public:
+
+  /* 
+    This constructor creates an unlinked BKA join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+    The MRR mode initially is set to 'flags'.
+  */   
+  JOIN_CACHE_BKA(JOIN *j, JOIN_TAB *tab, uint flags)
+    :JOIN_CACHE(j, tab), mrr_mode(flags) {}
+  /* 
+    This constructor creates a linked BKA join cache. The cache is to be 
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+    The MRR mode initially is set to 'flags'.
+  */   
+  JOIN_CACHE_BKA(JOIN *j, JOIN_TAB *tab, uint flags, JOIN_CACHE *prev)
+    :JOIN_CACHE(j, tab, prev), mrr_mode(flags) {}
+  
+  JOIN_CACHE_BKA(JOIN_CACHE_BKA *bka)
+    :JOIN_CACHE(bka->join, bka->join_tab, bka->prev_cache),
+      mrr_mode(bka->mrr_mode)  {}
+
+  uchar **get_curr_association_ptr() { return &curr_association; }
+
+  /* Initialize the BKA cache */       
+  int init(bool for_explain);
+
+  enum Join_algorithm get_join_alg() { return BKA_JOIN_ALG; }
+
+  bool is_key_access() { return TRUE; }
+
+  /* Get the key built over the next record from the join buffer */
+  uint get_next_key(uchar **key);
+
+  /* Check index condition of the joined table for a record from BKA cache */
+  bool skip_index_tuple(range_id_t range_info);
+
+  bool save_explain_data(EXPLAIN_BKA_TYPE *explain);
+};
+
+
+
+/*
+  The class JOIN_CACHE_BKAH is used when the BKAH join algorithm is
+  employed to perform a join operation   
+*/
+
+class JOIN_CACHE_BKAH :public JOIN_CACHE_BNLH
+{
+
+private:
+  /* Flag to to be passed to the companion JOIN_TAB_SCAN_MRR object */
+  uint mrr_mode;
+
+  /* 
+    This flag is set to TRUE if the implementation of the MRR interface cannot
+    handle range association labels and does not return them to the caller of
+    the multi_range_read_next handler function. E.g. the implementation of
+    the MRR inteface for the Falcon engine could not return association
+    labels to the caller of multi_range_read_next.
+    The flag is set by JOIN_CACHE_BKA::init() and is not ever changed.
+  */       
+  bool no_association;
+
+  /* 
+    This field contains the association label returned by the 
+    multi_range_read_next function.
+    See the function JOIN_CACHE_BKAH::get_curr_key_association()
+  */
+  uchar *curr_matching_chain;
+
+protected:
+
+  uint get_number_of_ranges_for_mrr() { return key_entries; }
+
+  /* 
+    Initialize the MRR buffer allocating some space within the join buffer.
+    The entire space between the last record put into the join buffer and the
+    last key entry added to the hash table is used for the MRR buffer.
+  */
+  int setup_aux_buffer(HANDLER_BUFFER &aux_buff)
+  {
+    aux_buff.buffer= end_pos;
+    aux_buff.buffer_end= last_key_entry;
+    return 0;
+  }
+
+  bool prepare_look_for_matches(bool skip_last);
+
+  /*
+    The implementations of the methods
+    - get_next_candidate_for_match
+    - skip_recurrent_candidate_for_match
+    - read_next_candidate_for_match
+    are inherited from the JOIN_CACHE_BNLH class
+  */
+
+public:
+
+  /* 
+    This constructor creates an unlinked BKAH join cache. The cache is to be
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter.
+    The MRR mode initially is set to 'flags'.
+  */   
+  JOIN_CACHE_BKAH(JOIN *j, JOIN_TAB *tab, uint flags) 
+    :JOIN_CACHE_BNLH(j, tab), mrr_mode(flags) {}
+
+  /* 
+    This constructor creates a linked BKAH join cache. The cache is to be 
+    used to join table 'tab' to the result of joining the previous tables 
+    specified by the 'j' parameter. The parameter 'prev' specifies the previous
+    cache object to which this cache is linked.
+    The MRR mode initially is set to 'flags'.
+  */   
+  JOIN_CACHE_BKAH(JOIN *j, JOIN_TAB *tab, uint flags, JOIN_CACHE *prev)
+    :JOIN_CACHE_BNLH(j, tab, prev), mrr_mode(flags)  {}
+
+  JOIN_CACHE_BKAH(JOIN_CACHE_BKAH *bkah)
+    :JOIN_CACHE_BNLH(bkah->join, bkah->join_tab, bkah->prev_cache),
+      mrr_mode(bkah->mrr_mode)  {}
+
+  uchar **get_curr_association_ptr() { return &curr_matching_chain; }
+
+  /* Initialize the BKAH cache */       
+  int init(bool for_explain);
+
+  enum Join_algorithm get_join_alg() { return BKAH_JOIN_ALG; }
+
+  /* Check index condition of the joined table for a record from BKAH cache */
+  bool skip_index_tuple(range_id_t range_info);
+
+  bool save_explain_data(EXPLAIN_BKA_TYPE *explain);
+};