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, 995 insertions, 0 deletions

diff --git a/storage/maria/trnman.c b/storage/maria/trnman.c
new file mode 100644
index 00000000..7cac6a2d
--- /dev/null
+++ b/storage/maria/trnman.c
@@ -0,0 +1,995 @@
+/* Copyright (C) 2006-2008 MySQL AB, 2008-2009 Sun Microsystems, Inc.
+
+   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 */
+
+
+#include <my_global.h>
+#include <my_sys.h>
+#include <m_string.h>
+#include "trnman.h"
+#include "ma_checkpoint.h"
+#include "ma_control_file.h"
+
+/*
+  status variables:
+  how many trns in the active list currently,
+  in the committed list currently, allocated since startup.
+*/
+uint trnman_active_transactions, trnman_committed_transactions,
+  trnman_allocated_transactions;
+
+#ifdef WORKAROUND_GCC_4_3_2_BUG
+volatile
+#endif
+/* list of active transactions in the trid order */
+static TRN active_list_min, active_list_max;
+/* list of committed transactions in the trid order */
+static TRN committed_list_min, committed_list_max;
+
+/* a counter, used to generate transaction ids */
+static TrID global_trid_generator;
+
+/*
+  The minimum existing transaction id for trnman_get_min_trid()
+  The default value is used when transaction manager not initialize;
+  Probably called from maria_chk
+*/
+static TrID trid_min_read_from= MAX_TRID;
+
+/* the mutex for everything above */
+static mysql_mutex_t LOCK_trn_list;
+
+/* LIFO pool of unused TRN structured for reuse */
+static TRN *pool;
+
+/* a hash for committed transactions that maps trid to a TRN structure */
+static LF_HASH trid_to_trn;
+
+/* an array that maps short_id of an active transaction to a TRN structure */
+static TRN **short_trid_to_active_trn;
+
+/* locks for short_trid_to_active_trn and pool */
+static my_bool default_trnman_end_trans_hook(TRN *, my_bool, my_bool);
+static void trnman_free_trn(TRN *);
+
+my_bool (*trnman_end_trans_hook)(TRN *, my_bool, my_bool)=
+  default_trnman_end_trans_hook;
+
+/*
+  Simple interface functions
+  QQ: if they stay so simple, should we make them inline?
+*/
+
+uint trnman_increment_locked_tables(TRN *trn)
+{
+  return trn->locked_tables++;
+}
+
+uint trnman_has_locked_tables(TRN *trn)
+{
+  return trn->locked_tables;
+}
+
+uint trnman_decrement_locked_tables(TRN *trn)
+{
+  return --trn->locked_tables;
+}
+
+void trnman_reset_locked_tables(TRN *trn, uint locked_tables)
+{
+  trn->locked_tables= locked_tables;
+}
+
+#ifdef EXTRA_DEBUG
+uint16 trnman_get_flags(TRN *trn)
+{
+  return trn->flags;
+}
+
+void trnman_set_flags(TRN *trn, uint16 flags)
+{
+  trn->flags= flags;
+}
+#endif
+
+/** Wake up threads waiting for this transaction */
+static void wt_thd_release_self(TRN *trn)
+{
+  if (trn->wt)
+  {
+    WT_RESOURCE_ID rc;
+    rc.type= &ma_rc_dup_unique;
+    rc.value= (intptr)trn;
+    wt_thd_release(trn->wt, & rc);
+    trn->wt= 0;
+  }
+}
+
+static my_bool
+default_trnman_end_trans_hook(TRN *trn __attribute__ ((unused)),
+                              my_bool commit __attribute__ ((unused)),
+                              my_bool active_transactions
+                              __attribute__ ((unused)))
+{
+  return 0;
+}
+
+
+static uchar *trn_get_hash_key(const uchar *trn, size_t *len,
+                              my_bool unused __attribute__ ((unused)))
+{
+  *len= sizeof(TrID);
+  return (uchar *) & ((*((TRN **)trn))->trid);
+}
+
+
+/**
+   @brief Initializes transaction manager.
+
+   @param  initial_trid        Generated TrIDs will start from initial_trid+1.
+
+   @return Operation status
+     @retval 0      OK
+     @retval !=0    Error
+*/
+
+int trnman_init(TrID initial_trid)
+{
+  DBUG_ENTER("trnman_init");
+  DBUG_PRINT("enter", ("initial_trid: %lu", (ulong) initial_trid));
+
+  short_trid_to_active_trn= (TRN **)my_malloc(PSI_INSTRUMENT_ME, SHORT_TRID_MAX*sizeof(TRN*),
+                                     MYF(MY_WME|MY_ZEROFILL));
+  if (unlikely(!short_trid_to_active_trn))
+    DBUG_RETURN(1);
+  short_trid_to_active_trn--; /* min short_id is 1 */
+
+  /*
+    Initialize lists.
+    active_list_max.min_read_from must be larger than any trid,
+    so that when an active list is empty we would could free
+    all committed list.
+    And  committed_list_max itself can not be freed so
+    committed_list_max.commit_trid must not be smaller that
+    active_list_max.min_read_from
+  */
+
+  active_list_max.trid= active_list_min.trid= 0;
+  active_list_max.min_read_from= MAX_TRID;
+  active_list_max.next= active_list_min.prev= 0;
+  active_list_max.prev= &active_list_min;
+  active_list_min.next= &active_list_max;
+
+  committed_list_max.commit_trid= MAX_TRID;
+  committed_list_max.next= committed_list_min.prev= 0;
+  committed_list_max.prev= &committed_list_min;
+  committed_list_min.next= &committed_list_max;
+
+  trnman_active_transactions= 0;
+  trnman_committed_transactions= 0;
+  trnman_allocated_transactions= 0;
+  /* This is needed for recovery and repair */
+  dummy_transaction_object.min_read_from= ~(TrID) 0;
+  dummy_transaction_object.first_undo_lsn= TRANSACTION_LOGGED_LONG_ID;
+
+  pool= 0;
+  global_trid_generator= initial_trid;
+  trid_min_read_from= initial_trid;
+  lf_hash_init(&trid_to_trn, sizeof(TRN*), LF_HASH_UNIQUE,
+               0, 0, trn_get_hash_key, 0);
+  DBUG_PRINT("info", ("mysql_mutex_init LOCK_trn_list"));
+  mysql_mutex_init(key_LOCK_trn_list, &LOCK_trn_list, MY_MUTEX_INIT_FAST);
+
+  DBUG_RETURN(0);
+}
+
+
+/*
+  NOTE
+    this could only be called in the "idle" state - no transaction can be
+    running. See asserts below.
+*/
+void trnman_destroy()
+{
+  DBUG_ENTER("trnman_destroy");
+
+  if (short_trid_to_active_trn == NULL) /* trnman already destroyed */
+    DBUG_VOID_RETURN;
+  DBUG_ASSERT(trid_to_trn.count == 0);
+  DBUG_ASSERT(trnman_active_transactions == 0);
+  DBUG_ASSERT(trnman_committed_transactions == 0);
+  DBUG_ASSERT(active_list_max.prev == &active_list_min);
+  DBUG_ASSERT(active_list_min.next == &active_list_max);
+  DBUG_ASSERT(committed_list_max.prev == &committed_list_min);
+  DBUG_ASSERT(committed_list_min.next == &committed_list_max);
+  while (pool)
+  {
+    TRN *trn= pool;
+    pool= pool->next;
+    DBUG_ASSERT(trn->wt == NULL);
+    mysql_mutex_destroy(&trn->state_lock);
+    my_free(trn);
+  }
+  lf_hash_destroy(&trid_to_trn);
+  DBUG_PRINT("info", ("mysql_mutex_destroy LOCK_trn_list"));
+  mysql_mutex_destroy(&LOCK_trn_list);
+  my_free(short_trid_to_active_trn+1);
+  short_trid_to_active_trn= NULL;
+
+  DBUG_VOID_RETURN;
+}
+
+
+/*
+  NOTE
+    TrID is limited to 6 bytes. Initial value of the generator
+    is set by the recovery code - being read from the last checkpoint
+    (or 1 on a first run).
+*/
+static TrID new_trid()
+{
+  DBUG_ENTER("new_trid");
+  DBUG_ASSERT(global_trid_generator < MAX_INTERNAL_TRID);
+  DBUG_PRINT("info", ("mysql_mutex_assert_owner LOCK_trn_list"));
+  mysql_mutex_assert_owner(&LOCK_trn_list);
+  DBUG_RETURN(++global_trid_generator);
+}
+
+static uint get_short_trid(TRN *trn)
+{
+  int i= (int) ((global_trid_generator + (intptr)trn) * 312089 %
+                SHORT_TRID_MAX) + 1;
+  uint res=0;
+
+  for ( ; !res ; i= 1)
+  {
+    for ( ; i <= SHORT_TRID_MAX; i++) /* the range is [1..SHORT_TRID_MAX] */
+    {
+      void *tmp= NULL;
+      if (short_trid_to_active_trn[i] == NULL &&
+          my_atomic_casptr((void **)&short_trid_to_active_trn[i], &tmp, trn))
+      {
+        res= i;
+        break;
+      }
+    }
+  }
+  return res;
+}
+
+/**
+  Allocates and initializes a new TRN object
+
+  @note the 'wt' parameter can only be 0 in a single-threaded code (or,
+  generally, where threads cannot block each other), otherwise the
+  first call to the deadlock detector will sigsegv.
+*/
+
+TRN *trnman_new_trn(WT_THD *wt)
+{
+  int res;
+  TRN *trn;
+  union { TRN *trn; void *v; } tmp;
+  DBUG_ENTER("trnman_new_trn");
+
+  /*
+    we have a mutex, to do simple things under it - allocate a TRN,
+    increment trnman_active_transactions, set trn->min_read_from.
+
+    Note that all the above is fast. generating short_id may be slow,
+    as it involves scanning a large array - so it's done outside of the
+    mutex.
+  */
+
+  DBUG_PRINT("info", ("mysql_mutex_lock LOCK_trn_list"));
+  mysql_mutex_lock(&LOCK_trn_list);
+
+  /* Allocating a new TRN structure */
+  tmp.trn= pool;
+  /*
+    Popping an unused TRN from the pool
+    (ABA isn't possible, we're behind a mutex
+  */
+  while (tmp.trn && !my_atomic_casptr((void **)(char*) &pool, &tmp.v,
+                                      (void *)tmp.trn->next))
+    /* no-op */;
+
+  /* Nothing in the pool ? Allocate a new one */
+  if (!(trn= tmp.trn))
+  {
+    /*
+      trn should be completely initialized at create time to allow
+      one to keep a known state on it.
+      (Like redo_lns, which is assumed to be 0 at start of row handling
+      and reset to zero before end of row handling)
+    */
+    trn= (TRN *)my_malloc(PSI_INSTRUMENT_ME, sizeof(TRN), MYF(MY_WME | MY_ZEROFILL));
+    if (unlikely(!trn))
+    {
+      DBUG_PRINT("info", ("mysql_mutex_unlock LOCK_trn_list"));
+      mysql_mutex_unlock(&LOCK_trn_list);
+      return 0;
+    }
+    trnman_allocated_transactions++;
+    mysql_mutex_init(key_TRN_state_lock, &trn->state_lock, MY_MUTEX_INIT_FAST);
+  }
+  trn->wt= wt;
+  trn->pins= lf_hash_get_pins(&trid_to_trn);
+  if (!trn->pins)
+  {
+    trnman_free_trn(trn);
+    mysql_mutex_unlock(&LOCK_trn_list);
+    return 0;
+  }
+
+  trnman_active_transactions++;
+
+  trn->min_read_from= active_list_min.next->trid;
+
+  trn->trid= new_trid();
+
+  trn->next= &active_list_max;
+  trn->prev= active_list_max.prev;
+  active_list_max.prev= trn->prev->next= trn;
+  trid_min_read_from= active_list_min.next->min_read_from;
+  DBUG_PRINT("info", ("mysql_mutex_unlock LOCK_trn_list"));
+  mysql_mutex_unlock(&LOCK_trn_list);
+
+  if (unlikely(!trn->min_read_from))
+  {
+    /*
+      We are the only transaction. Set min_read_from so that we can read
+      our own rows
+    */
+    trn->min_read_from= trn->trid + 1;
+  }
+
+  /* no other transaction can read changes done by this one */
+  trn->commit_trid=  MAX_TRID;
+  trn->rec_lsn= trn->undo_lsn= trn->first_undo_lsn= 0;
+  trn->used_tables= 0;
+  trn->used_instances= 0;
+
+  trn->locked_tables= 0;
+  trn->flags= 0;
+
+  /*
+    only after the following function TRN is considered initialized,
+    so it must be done the last
+  */
+  mysql_mutex_lock(&trn->state_lock);
+  trn->short_id= get_short_trid(trn);
+  mysql_mutex_unlock(&trn->state_lock);
+
+  res= lf_hash_insert(&trid_to_trn, trn->pins, &trn);
+  DBUG_ASSERT(res <= 0);
+  if (res)
+  {
+    trnman_end_trn(trn, 0);
+    return 0;
+  }
+
+  DBUG_PRINT("exit", ("trn: %p  trid: 0x%lu  min_read_from: 0x%lu",
+                      trn, (ulong) trn->trid, (ulong) trn->min_read_from));
+
+  DBUG_RETURN(trn);
+}
+
+
+/*
+  Initialize a temporary TRN object for logging a new transaction id (trid)
+  to it. Used by create table to associate a create trid to the table.
+
+  Out: trn->trid is updated with next available trid
+*/
+
+void trnman_init_tmp_trn_for_logging_trid(TRN *trn)
+{
+  *trn= dummy_transaction_object;
+  /* Avoid logging short_id */
+  trn->short_id= 1;
+  /* Trid gets logged in translog_write_record */
+  trn->first_undo_lsn= 0;
+  /* Get next free trid */
+  trn->trid= trnman_get_min_safe_trid();
+}
+
+
+/*
+  remove a trn from the active list.
+  if necessary - move to committed list and set commit_trid
+
+  NOTE
+    Locks are released at the end. In particular, after placing the
+    transaction in commit list, and after setting commit_trid. It's
+    important, as commit_trid affects visibility.  Locks don't affect
+    anything they simply delay execution of other threads - they could be
+    released arbitrarily late. In other words, when locks are released it
+    serves as a start banner for other threads, they start to run. So
+    everything they may need must be ready at that point.
+
+  RETURN
+    0  ok
+    1  error
+*/
+my_bool trnman_end_trn(TRN *trn, my_bool commit)
+{
+  int res= 1;
+  uint16 cached_short_id= trn->short_id; /* we have to cache it, see below */
+  TRN *free_me= 0;
+  LF_PINS *pins= trn->pins;
+  DBUG_ENTER("trnman_end_trn");
+  DBUG_PRINT("enter", ("trn: %p  commit: %d", trn, commit));
+
+  /* if a rollback, all UNDO records should have been executed */
+  DBUG_ASSERT(commit || trn->undo_lsn == 0);
+  DBUG_ASSERT(trn != &dummy_transaction_object);
+  DBUG_ASSERT(trn->locked_tables == 0 && trn->used_instances == 0);
+  DBUG_PRINT("info", ("mysql_mutex_lock LOCK_trn_list"));
+
+  mysql_mutex_lock(&LOCK_trn_list);
+
+  /* remove from active list */
+  trn->next->prev= trn->prev;
+  trn->prev->next= trn->next;
+
+  /*
+    if trn was the oldest active transaction, now that it goes away there
+    may be committed transactions in the list which no active transaction
+    needs to bother about - clean up the committed list
+  */
+  if (trn->prev == &active_list_min)
+  {
+    uint free_me_count;
+    TRN *t;
+    for (t= committed_list_min.next, free_me_count= 0;
+         t->commit_trid < active_list_min.next->min_read_from;
+         t= t->next, free_me_count++) /* no-op */;
+
+    DBUG_ASSERT((t != committed_list_min.next && free_me_count > 0) ||
+                (t == committed_list_min.next && free_me_count == 0));
+    /* found transactions committed before the oldest active one */
+    if (t != committed_list_min.next)
+    {
+      free_me= committed_list_min.next;
+      committed_list_min.next= t;
+      t->prev->next= 0;
+      t->prev= &committed_list_min;
+      trnman_committed_transactions-= free_me_count;
+    }
+  }
+
+  mysql_mutex_lock(&trn->state_lock);
+  if (commit)
+    trn->commit_trid= global_trid_generator;
+  wt_thd_release_self(trn);
+  mysql_mutex_unlock(&trn->state_lock);
+
+  /*
+    if transaction is committed and it was not the only active transaction -
+    add it to the committed list
+  */
+  if (commit && active_list_min.next != &active_list_max)
+  {
+    trn->next= &committed_list_max;
+    trn->prev= committed_list_max.prev;
+    trnman_committed_transactions++;
+    committed_list_max.prev= trn->prev->next= trn;
+  }
+  else
+  {
+    trn->next= free_me;
+    free_me= trn;
+  }
+  trid_min_read_from= active_list_min.next->min_read_from;
+
+  if ((*trnman_end_trans_hook)(trn, commit,
+                               active_list_min.next != &active_list_max))
+    res= -1;
+  trnman_active_transactions--;
+
+  DBUG_PRINT("info", ("mysql_mutex_unlock LOCK_trn_list"));
+  mysql_mutex_unlock(&LOCK_trn_list);
+
+  /*
+    the rest is done outside of a critical section
+
+    note that we don't own trn anymore, it may be in a shared list now.
+    Thus, we cannot dereference it, and must use cached_short_id below.
+  */
+  my_atomic_storeptr((void **)&short_trid_to_active_trn[cached_short_id], 0);
+
+  /*
+    we, under the mutex, removed going-in-free_me transactions from the
+    active and committed lists, thus nobody else may see them when it scans
+    those lists, and thus nobody may want to free them. Now we don't
+    need a mutex to access free_me list
+  */
+  /* QQ: send them to the purge thread */
+  while (free_me)
+  {
+    TRN *t= free_me;
+    free_me= free_me->next;
+
+    /* ignore OOM. it's harmless, and we can do nothing here anyway */
+    (void)lf_hash_delete(&trid_to_trn, pins, &t->trid, sizeof(TrID));
+
+    trnman_free_trn(t);
+  }
+
+  lf_hash_put_pins(pins);
+
+  DBUG_RETURN(res < 0);
+}
+
+/*
+  free a trn (add to the pool, that is)
+  note - we can never really free() a TRN if there's at least one other
+  running transaction - see, e.g., how lock waits are implemented in
+  lockman.c
+  The same is true for other lock-free data structures too. We may need some
+  kind of FLUSH command to reset them all - ensuring that no transactions are
+  running. It may even be called automatically on checkpoints if no
+  transactions are running.
+*/
+static void trnman_free_trn(TRN *trn)
+{
+  /*
+     union is to solve strict aliasing issue.
+     without it gcc 3.4.3 doesn't notice that updating *(void **)&tmp
+     modifies the value of tmp.
+  */
+  union { TRN *trn; void *v; } tmp;
+
+  DBUG_ASSERT(trn != &dummy_transaction_object);
+
+  mysql_mutex_lock(&trn->state_lock);
+  trn->short_id= 0;
+  mysql_mutex_unlock(&trn->state_lock);
+
+  tmp.trn= pool;
+
+  do
+  {
+    /*
+      without this volatile cast gcc-3.4.4 moves the assignment
+      down after the loop at -O2
+    */
+    *(TRN * volatile *)&(trn->next)= tmp.trn;
+  } while (!my_atomic_casptr((void **)(char*)&pool, &tmp.v, trn));
+}
+
+/*
+  NOTE
+    here we access the hash in a lock-free manner.
+    It's safe, a 'found' TRN can never be freed/reused before we access it.
+    In fact, it cannot be freed before 'trn' ends, because a 'found' TRN
+    can only be removed from the hash when:
+                found->commit_trid < ALL (trn->min_read_from)
+    that is, at least
+                found->commit_trid < trn->min_read_from
+    but
+                found->trid >= trn->min_read_from
+    and
+                found->commit_trid > found->trid
+
+  RETURN
+    1   can
+    0   cannot
+   -1   error (OOM)
+*/
+int trnman_can_read_from(TRN *trn, TrID trid)
+{
+  TRN **found;
+  my_bool can;
+
+  if (trid < trn->min_read_from)
+    return 1; /* Row is visible by all transactions in the system */
+
+  if (trid >= trn->trid)
+  {
+    /*
+      We have now two cases
+      trid > trn->trid, in which case the row is from a new transaction
+      and not visible, in which case we should return 0.
+      trid == trn->trid in which case the row is from the current transaction
+      and we should return 1
+    */
+    return trid == trn->trid;
+  }
+
+  found= lf_hash_search(&trid_to_trn, trn->pins, &trid, sizeof(trid));
+  if (found == NULL)
+    return 0; /* not in the hash of transactions = cannot read */
+  if (found == MY_ERRPTR)
+    return -1;
+
+  can= (*found)->commit_trid < trn->trid;
+  lf_hash_search_unpin(trn->pins);
+  return can;
+}
+
+/**
+  Finds a TRN by its TrID
+
+  @param trn    current trn. Needed for pinning pointers (see lf_pin)
+  @param trid   trid to search for
+
+  @return found trn or 0
+
+  @note that trn is returned with its state locked!
+*/
+TRN *trnman_trid_to_trn(TRN *trn, TrID trid)
+{
+  TRN **found;
+
+  if (trid < trn->min_read_from)
+    return 0; /* it's committed eons ago */
+
+  found= lf_hash_search(&trid_to_trn, trn->pins, &trid, sizeof(trid));
+  if (found == NULL || found == MY_ERRPTR)
+    return 0; /* no luck */
+
+  /* we've found something */
+  mysql_mutex_lock(&(*found)->state_lock);
+
+  if ((*found)->short_id == 0)
+  {
+    mysql_mutex_unlock(&(*found)->state_lock);
+    lf_hash_search_unpin(trn->pins);
+    return 0; /* but it was a ghost */
+  }
+  lf_hash_search_unpin(trn->pins);
+
+  /* Gotcha! */
+  return *found;
+}
+
+/* TODO: the stubs below are waiting for savepoints to be implemented */
+
+void trnman_new_statement(TRN *trn __attribute__ ((unused)))
+{
+}
+
+void trnman_rollback_statement(TRN *trn __attribute__ ((unused)))
+{
+}
+
+
+/**
+   @brief Allocates buffers and stores in them some info about transactions
+
+   Does the allocation because the caller cannot know the size itself.
+   Memory freeing is to be done by the caller (if the "str" member of the
+   LEX_STRING is not NULL).
+   The caller has the intention of doing checkpoints.
+
+   @param[out]  str_act    pointer to where the allocated buffer,
+                           and its size, will be put; buffer will be filled
+                           with info about active transactions
+   @param[out]  str_com    pointer to where the allocated buffer,
+                           and its size, will be put; buffer will be filled
+                           with info about committed transactions
+   @param[out]  min_first_undo_lsn pointer to where the minimum
+                           first_undo_lsn of all transactions will be put
+
+   @return Operation status
+     @retval 0      OK
+     @retval 1      Error
+*/
+
+my_bool trnman_collect_transactions(LEX_STRING *str_act, LEX_STRING *str_com,
+                                    LSN *min_rec_lsn, LSN *min_first_undo_lsn)
+{
+  my_bool error;
+  TRN *trn;
+  char *ptr;
+  uint stored_transactions= 0;
+  LSN minimum_rec_lsn= LSN_MAX, minimum_first_undo_lsn= LSN_MAX;
+  DBUG_ENTER("trnman_collect_transactions");
+
+  DBUG_ASSERT((NULL == str_act->str) && (NULL == str_com->str));
+
+  /* validate the use of read_non_atomic() in general: */
+  compile_time_assert((sizeof(LSN) == 8) && (sizeof(LSN_WITH_FLAGS) == 8));
+  mysql_mutex_lock(&LOCK_trn_list);
+  str_act->length= 2 + /* number of active transactions */
+    LSN_STORE_SIZE + /* minimum of their rec_lsn */
+    TRANSID_SIZE + /* current TrID generator value */
+    (2 + /* short id */
+     6 + /* long id */
+     LSN_STORE_SIZE + /* undo_lsn */
+#ifdef MARIA_VERSIONING /* not enabled yet */
+     LSN_STORE_SIZE + /* undo_purge_lsn */
+#endif
+     LSN_STORE_SIZE /* first_undo_lsn */
+     ) * trnman_active_transactions;
+  str_com->length= 4 + /* number of committed transactions */
+    (6 + /* long id */
+#ifdef MARIA_VERSIONING /* not enabled yet */
+     LSN_STORE_SIZE + /* undo_purge_lsn */
+#endif
+     LSN_STORE_SIZE /* first_undo_lsn */
+     ) * trnman_committed_transactions;
+  if ((NULL == (str_act->str= my_malloc(PSI_INSTRUMENT_ME, str_act->length, MYF(MY_WME)))) ||
+      (NULL == (str_com->str= my_malloc(PSI_INSTRUMENT_ME, str_com->length, MYF(MY_WME)))))
+    goto err;
+  /* First, the active transactions */
+  ptr= str_act->str + 2 + LSN_STORE_SIZE;
+  transid_store(ptr, global_trid_generator);
+  ptr+= TRANSID_SIZE;
+  for (trn= active_list_min.next; trn != &active_list_max; trn= trn->next)
+  {
+    uint sid;
+    LSN rec_lsn, undo_lsn, first_undo_lsn;
+    mysql_mutex_lock(&trn->state_lock);
+    sid= trn->short_id;
+    mysql_mutex_unlock(&trn->state_lock);
+    if (sid == 0)
+    {
+      /*
+        Not even inited, has done nothing. Or it is the
+        dummy_transaction_object, which does only non-transactional
+        immediate-sync operations (CREATE/DROP/RENAME/REPAIR TABLE), and so
+        can be forgotten for Checkpoint.
+      */
+      continue;
+    }
+    /* needed for low-water mark calculation */
+    if (((rec_lsn= lsn_read_non_atomic(trn->rec_lsn)) > 0) &&
+        (cmp_translog_addr(rec_lsn, minimum_rec_lsn) < 0))
+      minimum_rec_lsn= rec_lsn;
+    /*
+      If trn has not logged LOGREC_LONG_TRANSACTION_ID, this trn will be
+      discovered when seeing that log record which is for sure located after
+      checkpoint_start_log_horizon.
+    */
+    if ((LSN_WITH_FLAGS_TO_FLAGS(trn->first_undo_lsn) &
+         TRANSACTION_LOGGED_LONG_ID) == 0)
+      continue;
+    /*
+      On the other hand, if undo_lsn is LSN_IMPOSSIBLE, trn may later log
+      records; so we must include trn in the checkpoint now, because we cannot
+      count on LOGREC_LONG_TRANSACTION_ID (as we are already past it).
+    */
+    undo_lsn= trn->undo_lsn;
+    stored_transactions++;
+    int2store(ptr, sid);
+    ptr+= 2;
+    int6store(ptr, trn->trid);
+    ptr+= 6;
+    lsn_store(ptr, undo_lsn); /* needed for rollback */
+    ptr+= LSN_STORE_SIZE;
+    /* needed for low-water mark calculation */
+    if (((first_undo_lsn= lsn_read_non_atomic(trn->first_undo_lsn)) > 0) &&
+        (cmp_translog_addr(first_undo_lsn, minimum_first_undo_lsn) < 0))
+      minimum_first_undo_lsn= first_undo_lsn;
+    lsn_store(ptr, first_undo_lsn);
+    ptr+= LSN_STORE_SIZE;
+#ifdef MARIA_VERSIONING /* not enabled yet */
+    /* to know where purging should start (last delete of this trn) */
+    lsn_store(ptr, trn->undo_purge_lsn);
+    ptr+= LSN_STORE_SIZE;
+#endif
+    /**
+       @todo RECOVERY: add a comment explaining why we can dirtily read some
+       vars, inspired by the text of "assumption 8" in WL#3072
+    */
+  }
+  str_act->length= ptr - str_act->str; /* as we maybe over-estimated */
+  ptr= str_act->str;
+  DBUG_PRINT("info",("collected %u active transactions",
+                     (uint)stored_transactions));
+  int2store(ptr, stored_transactions);
+  ptr+= 2;
+  /* this LSN influences how REDOs for any page can be ignored by Recovery */
+  lsn_store(ptr, minimum_rec_lsn);
+  /* one day there will also be a list of prepared transactions */
+  /* do the same for committed ones */
+  ptr= str_com->str;
+  int4store(ptr, trnman_committed_transactions);
+  ptr+= 4;
+  DBUG_PRINT("info",("collected %u committed transactions",
+                     (uint)trnman_committed_transactions));
+  for (trn= committed_list_min.next; trn != &committed_list_max;
+       trn= trn->next)
+  {
+    LSN first_undo_lsn;
+    int6store(ptr, trn->trid);
+    ptr+= 6;
+#ifdef MARIA_VERSIONING /* not enabled yet */
+    lsn_store(ptr, trn->undo_purge_lsn);
+    ptr+= LSN_STORE_SIZE;
+#endif
+    first_undo_lsn= LSN_WITH_FLAGS_TO_LSN(trn->first_undo_lsn);
+    if (cmp_translog_addr(first_undo_lsn, minimum_first_undo_lsn) < 0)
+      minimum_first_undo_lsn= first_undo_lsn;
+    lsn_store(ptr, first_undo_lsn);
+    ptr+= LSN_STORE_SIZE;
+  }
+  /*
+    TODO: if we see there exists no transaction (active and committed) we can
+    tell the lock-free structures to do some freeing (my_free()).
+  */
+  error= 0;
+  *min_rec_lsn= minimum_rec_lsn;
+  *min_first_undo_lsn= minimum_first_undo_lsn;
+  goto end;
+err:
+  error= 1;
+end:
+  mysql_mutex_unlock(&LOCK_trn_list);
+  DBUG_RETURN(error);
+}
+
+
+TRN *trnman_recreate_trn_from_recovery(uint16 shortid, TrID longid)
+{
+  TrID old_trid_generator= global_trid_generator;
+  TRN *trn;
+  DBUG_ASSERT(maria_in_recovery && !maria_multi_threaded);
+  global_trid_generator= longid-1; /* force a correct trid in the new trn */
+  if (unlikely((trn= trnman_new_trn(NULL)) == NULL))
+    return NULL;
+  /* deallocate excessive allocations of trnman_new_trn() */
+  global_trid_generator= old_trid_generator;
+  set_if_bigger(global_trid_generator, longid);
+  short_trid_to_active_trn[trn->short_id]= 0;
+  DBUG_ASSERT(short_trid_to_active_trn[shortid] == NULL);
+  short_trid_to_active_trn[shortid]= trn;
+  trn->short_id= shortid;
+  return trn;
+}
+
+
+TRN *trnman_get_any_trn()
+{
+  TRN *trn= active_list_min.next;
+  return (trn != &active_list_max) ? trn : NULL;
+}
+
+
+/**
+  Returns the minimum existing transaction id. May return a too small
+  number in race conditions, but this is ok as the value is used to
+  remove not visible transid from index/rows.
+*/
+
+TrID trnman_get_min_trid()
+{
+  return trid_min_read_from;
+}
+
+
+/**
+  Returns the minimum possible transaction id
+
+  @notes
+  If there is no transactions running, returns number for next running
+  transaction.
+  If one has an active transaction, the returned number will be less or
+  equal to this.  If one is not running in a transaction one will ge the
+  number for the next started transaction.  This is used in create table
+  to get a safe minimum trid to use.
+*/
+
+TrID trnman_get_min_safe_trid()
+{
+  TrID trid;
+  mysql_mutex_lock(&LOCK_trn_list);
+  trid= MY_MIN(active_list_min.next->min_read_from,
+            global_trid_generator);
+  mysql_mutex_unlock(&LOCK_trn_list);
+  return trid;
+}
+
+
+/**
+  Returns maximum transaction id given to a transaction so far.
+*/
+
+TrID trnman_get_max_trid()
+{
+  TrID id;
+  /* Check if trnman has been initalized */
+  if (short_trid_to_active_trn == NULL)
+    return 0;
+  mysql_mutex_lock(&LOCK_trn_list);
+  id= global_trid_generator;
+  mysql_mutex_unlock(&LOCK_trn_list);
+  return id;
+}
+
+/**
+  @brief Check if there exist an active transaction between two commit_id's
+
+  @todo
+    Improve speed of this.
+      - Store transactions in tree or skip list
+      - Have function to copying all active transaction id's to b-tree
+        and use b-tree for checking states.  This could be a big win
+        for checkpoint that will call this function for a lot of objects.
+
+  @return
+    0   No transaction exists
+    1   There is at least on active transaction in the given range
+*/
+
+my_bool trnman_exists_active_transactions(TrID min_id, TrID max_id,
+                                          my_bool trnman_is_locked)
+{
+  TRN *trn;
+  my_bool ret= 0;
+
+  if (!trnman_is_locked)
+    mysql_mutex_lock(&LOCK_trn_list);
+  mysql_mutex_assert_owner(&LOCK_trn_list);
+  for (trn= active_list_min.next; trn != &active_list_max; trn= trn->next)
+  {
+    /*
+      We use <= for max_id as max_id is a commit_trid and trn->trid
+      is transaction id.  When calculating commit_trid we use the
+      current value of global_trid_generator.  global_trid_generator is
+      incremented for each new transaction.
+
+      For example, assuming we have
+      min_id = 5
+      max_id = 10
+
+      A trid of value 5 can't see the history event between 5 & 10
+      at it vas started before min_id 5 was committed.
+      A trid of value 10 can't see the next history event (max_id = 10)
+      as it started before this was committed. In this case it must use
+      the this event.
+    */
+    if (trn->trid > min_id && trn->trid <= max_id)
+    {
+      ret= 1;
+      break;
+    }
+  }
+  if (!trnman_is_locked)
+    mysql_mutex_unlock(&LOCK_trn_list);
+  return ret;
+}
+
+
+/**
+   lock transaction list
+*/
+
+void trnman_lock()
+{
+  mysql_mutex_lock(&LOCK_trn_list);
+}
+
+
+/**
+   unlock transaction list
+*/
+
+void trnman_unlock()
+{
+  mysql_mutex_unlock(&LOCK_trn_list);
+}
+
+
+/**
+  Is trman initialized
+*/
+
+my_bool trman_is_inited()
+{
+  return (short_trid_to_active_trn != NULL);
+}