mariadb/sql/transaction.cc
Dmitry Lenev 378cdc58c1 Patch that refactors global read lock implementation and fixes
bug #57006 "Deadlock between HANDLER and FLUSH TABLES WITH READ
LOCK" and bug #54673 "It takes too long to get readlock for
'FLUSH TABLES WITH READ LOCK'".

The first bug manifested itself as a deadlock which occurred
when a connection, which had some table open through HANDLER
statement, tried to update some data through DML statement
while another connection tried to execute FLUSH TABLES WITH
READ LOCK concurrently.

What happened was that FTWRL in the second connection managed
to perform first step of GRL acquisition and thus blocked all
upcoming DML. After that it started to wait for table open
through HANDLER statement to be flushed. When the first connection
tried to execute DML it has started to wait for GRL/the second
connection creating deadlock.

The second bug manifested itself as starvation of FLUSH TABLES
WITH READ LOCK statements in cases when there was a constant
stream of concurrent DML statements (in two or more
connections).

This has happened because requests for protection against GRL
which were acquired by DML statements were ignoring presence of
pending GRL and thus the latter was starved.

This patch solves both these problems by re-implementing GRL
using metadata locks.

Similar to the old implementation acquisition of GRL in new
implementation is two-step. During the first step we block
all concurrent DML and DDL statements by acquiring global S
metadata lock (each DML and DDL statement acquires global IX
lock for its duration). During the second step we block commits
by acquiring global S lock in COMMIT namespace (commit code
acquires global IX lock in this namespace).

Note that unlike in old implementation acquisition of
protection against GRL in DML and DDL is semi-automatic.
We assume that any statement which should be blocked by GRL
will either open and acquires write-lock on tables or acquires
metadata locks on objects it is going to modify. For any such
statement global IX metadata lock is automatically acquired
for its duration.

The first problem is solved because waits for GRL become
visible to deadlock detector in metadata locking subsystem
and thus deadlocks like one in the first bug become impossible.

The second problem is solved because global S locks which
are used for GRL implementation are given preference over
IX locks which are acquired by concurrent DML (and we can
switch to fair scheduling in future if needed).

Important change:
FTWRL/GRL no longer blocks DML and DDL on temporary tables.
Before this patch behavior was not consistent in this respect:
in some cases DML/DDL statements on temporary tables were
blocked while in others they were not. Since the main use cases
for FTWRL are various forms of backups and temporary tables are
not preserved during backups we have opted for consistently
allowing DML/DDL on temporary tables during FTWRL/GRL.

Important change:
This patch changes thread state names which are used when
DML/DDL of FTWRL is waiting for global read lock. It is now
either "Waiting for global read lock" or "Waiting for commit
lock" depending on the stage on which FTWRL is.

Incompatible change:
To solve deadlock in events code which was exposed by this
patch we have to replace LOCK_event_metadata mutex with
metadata locks on events. As result we have to prohibit
DDL on events under LOCK TABLES.

This patch also adds extensive test coverage for interaction
of DML/DDL and FTWRL.

Performance of new and old global read lock implementations
in sysbench tests were compared. There were no significant
difference between new and old implementations.
2010-11-11 20:11:05 +03:00

744 lines
19 KiB
C++

/* Copyright (C) 2008 Sun/MySQL
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation // gcc: Class implementation
#endif
#include "sql_priv.h"
#include "transaction.h"
#include "rpl_handler.h"
#include "debug_sync.h" // DEBUG_SYNC
/* Conditions under which the transaction state must not change. */
static bool trans_check(THD *thd)
{
enum xa_states xa_state= thd->transaction.xid_state.xa_state;
DBUG_ENTER("trans_check");
/*
Always commit statement transaction before manipulating with
the normal one.
*/
DBUG_ASSERT(thd->transaction.stmt.is_empty());
if (unlikely(thd->in_sub_stmt))
my_error(ER_COMMIT_NOT_ALLOWED_IN_SF_OR_TRG, MYF(0));
if (xa_state != XA_NOTR)
my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
else
DBUG_RETURN(FALSE);
DBUG_RETURN(TRUE);
}
/**
Mark a XA transaction as rollback-only if the RM unilaterally
rolled back the transaction branch.
@note If a rollback was requested by the RM, this function sets
the appropriate rollback error code and transits the state
to XA_ROLLBACK_ONLY.
@return TRUE if transaction was rolled back or if the transaction
state is XA_ROLLBACK_ONLY. FALSE otherwise.
*/
static bool xa_trans_rolled_back(XID_STATE *xid_state)
{
if (xid_state->rm_error)
{
switch (xid_state->rm_error) {
case ER_LOCK_WAIT_TIMEOUT:
my_error(ER_XA_RBTIMEOUT, MYF(0));
break;
case ER_LOCK_DEADLOCK:
my_error(ER_XA_RBDEADLOCK, MYF(0));
break;
default:
my_error(ER_XA_RBROLLBACK, MYF(0));
}
xid_state->xa_state= XA_ROLLBACK_ONLY;
}
return (xid_state->xa_state == XA_ROLLBACK_ONLY);
}
/**
Begin a new transaction.
@note Beginning a transaction implicitly commits any current
transaction and releases existing locks.
@param thd Current thread
@param flags Transaction flags
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_begin(THD *thd, uint flags)
{
int res= FALSE;
DBUG_ENTER("trans_begin");
if (trans_check(thd))
DBUG_RETURN(TRUE);
thd->locked_tables_list.unlock_locked_tables(thd);
DBUG_ASSERT(!thd->locked_tables_mode);
if (thd->in_multi_stmt_transaction_mode() ||
(thd->variables.option_bits & OPTION_TABLE_LOCK))
{
thd->variables.option_bits&= ~OPTION_TABLE_LOCK;
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
res= test(ha_commit_trans(thd, TRUE));
}
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
if (res)
DBUG_RETURN(TRUE);
/*
Release transactional metadata locks only after the
transaction has been committed.
*/
thd->mdl_context.release_transactional_locks();
thd->variables.option_bits|= OPTION_BEGIN;
thd->server_status|= SERVER_STATUS_IN_TRANS;
if (flags & MYSQL_START_TRANS_OPT_WITH_CONS_SNAPSHOT)
res= ha_start_consistent_snapshot(thd);
DBUG_RETURN(test(res));
}
/**
Commit the current transaction, making its changes permanent.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_commit(THD *thd)
{
int res;
DBUG_ENTER("trans_commit");
if (trans_check(thd))
DBUG_RETURN(TRUE);
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
res= ha_commit_trans(thd, TRUE);
if (res)
/*
if res is non-zero, then ha_commit_trans has rolled back the
transaction, so the hooks for rollback will be called.
*/
RUN_HOOK(transaction, after_rollback, (thd, FALSE));
else
RUN_HOOK(transaction, after_commit, (thd, FALSE));
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
thd->lex->start_transaction_opt= 0;
DBUG_RETURN(test(res));
}
/**
Implicitly commit the current transaction.
@note A implicit commit does not releases existing table locks.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_commit_implicit(THD *thd)
{
bool res= FALSE;
DBUG_ENTER("trans_commit_implicit");
if (trans_check(thd))
DBUG_RETURN(TRUE);
if (thd->in_multi_stmt_transaction_mode() ||
(thd->variables.option_bits & OPTION_TABLE_LOCK))
{
/* Safety if one did "drop table" on locked tables */
if (!thd->locked_tables_mode)
thd->variables.option_bits&= ~OPTION_TABLE_LOCK;
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
res= test(ha_commit_trans(thd, TRUE));
}
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
/*
Upon implicit commit, reset the current transaction
isolation level. We do not care about
@@session.completion_type since it's documented
to not have any effect on implicit commit.
*/
thd->tx_isolation= (enum_tx_isolation) thd->variables.tx_isolation;
DBUG_RETURN(res);
}
/**
Rollback the current transaction, canceling its changes.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_rollback(THD *thd)
{
int res;
DBUG_ENTER("trans_rollback");
if (trans_check(thd))
DBUG_RETURN(TRUE);
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
res= ha_rollback_trans(thd, TRUE);
RUN_HOOK(transaction, after_rollback, (thd, FALSE));
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
thd->lex->start_transaction_opt= 0;
DBUG_RETURN(test(res));
}
/**
Commit the single statement transaction.
@note Note that if the autocommit is on, then the following call
inside InnoDB will commit or rollback the whole transaction
(= the statement). The autocommit mechanism built into InnoDB
is based on counting locks, but if the user has used LOCK
TABLES then that mechanism does not know to do the commit.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_commit_stmt(THD *thd)
{
DBUG_ENTER("trans_commit_stmt");
int res= FALSE;
/*
We currently don't invoke commit/rollback at end of
a sub-statement. In future, we perhaps should take
a savepoint for each nested statement, and release the
savepoint when statement has succeeded.
*/
DBUG_ASSERT(! thd->in_sub_stmt);
if (thd->transaction.stmt.ha_list)
{
res= ha_commit_trans(thd, FALSE);
if (! thd->in_active_multi_stmt_transaction())
thd->tx_isolation= (enum_tx_isolation) thd->variables.tx_isolation;
}
if (res)
/*
if res is non-zero, then ha_commit_trans has rolled back the
transaction, so the hooks for rollback will be called.
*/
RUN_HOOK(transaction, after_rollback, (thd, FALSE));
else
RUN_HOOK(transaction, after_commit, (thd, FALSE));
thd->transaction.stmt.reset();
DBUG_RETURN(test(res));
}
/**
Rollback the single statement transaction.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_rollback_stmt(THD *thd)
{
DBUG_ENTER("trans_rollback_stmt");
/*
We currently don't invoke commit/rollback at end of
a sub-statement. In future, we perhaps should take
a savepoint for each nested statement, and release the
savepoint when statement has succeeded.
*/
DBUG_ASSERT(! thd->in_sub_stmt);
if (thd->transaction.stmt.ha_list)
{
ha_rollback_trans(thd, FALSE);
if (thd->transaction_rollback_request && !thd->in_sub_stmt)
ha_rollback_trans(thd, TRUE);
if (! thd->in_active_multi_stmt_transaction())
thd->tx_isolation= (enum_tx_isolation) thd->variables.tx_isolation;
}
RUN_HOOK(transaction, after_rollback, (thd, FALSE));
thd->transaction.stmt.reset();
DBUG_RETURN(FALSE);
}
/* Find a named savepoint in the current transaction. */
static SAVEPOINT **
find_savepoint(THD *thd, LEX_STRING name)
{
SAVEPOINT **sv= &thd->transaction.savepoints;
while (*sv)
{
if (my_strnncoll(system_charset_info, (uchar *) name.str, name.length,
(uchar *) (*sv)->name, (*sv)->length) == 0)
break;
sv= &(*sv)->prev;
}
return sv;
}
/**
Set a named transaction savepoint.
@param thd Current thread
@param name Savepoint name
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_savepoint(THD *thd, LEX_STRING name)
{
SAVEPOINT **sv, *newsv;
DBUG_ENTER("trans_savepoint");
if (!(thd->in_multi_stmt_transaction_mode() || thd->in_sub_stmt) ||
!opt_using_transactions)
DBUG_RETURN(FALSE);
sv= find_savepoint(thd, name);
if (*sv) /* old savepoint of the same name exists */
{
newsv= *sv;
ha_release_savepoint(thd, *sv);
*sv= (*sv)->prev;
}
else if ((newsv= (SAVEPOINT *) alloc_root(&thd->transaction.mem_root,
savepoint_alloc_size)) == NULL)
{
my_error(ER_OUT_OF_RESOURCES, MYF(0));
DBUG_RETURN(TRUE);
}
newsv->name= strmake_root(&thd->transaction.mem_root, name.str, name.length);
newsv->length= name.length;
/*
if we'll get an error here, don't add new savepoint to the list.
we'll lose a little bit of memory in transaction mem_root, but it'll
be free'd when transaction ends anyway
*/
if (ha_savepoint(thd, newsv))
DBUG_RETURN(TRUE);
newsv->prev= thd->transaction.savepoints;
thd->transaction.savepoints= newsv;
/*
Remember locks acquired before the savepoint was set.
They are used as a marker to only release locks acquired after
the setting of this savepoint.
Note: this works just fine if we're under LOCK TABLES,
since mdl_savepoint() is guaranteed to be beyond
the last locked table. This allows to release some
locks acquired during LOCK TABLES.
*/
newsv->mdl_savepoint= thd->mdl_context.mdl_savepoint();
DBUG_RETURN(FALSE);
}
/**
Rollback a transaction to the named savepoint.
@note Modifications that the current transaction made to
rows after the savepoint was set are undone in the
rollback.
@note Savepoints that were set at a later time than the
named savepoint are deleted.
@param thd Current thread
@param name Savepoint name
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_rollback_to_savepoint(THD *thd, LEX_STRING name)
{
int res= FALSE;
SAVEPOINT *sv= *find_savepoint(thd, name);
DBUG_ENTER("trans_rollback_to_savepoint");
if (sv == NULL)
{
my_error(ER_SP_DOES_NOT_EXIST, MYF(0), "SAVEPOINT", name.str);
DBUG_RETURN(TRUE);
}
if (ha_rollback_to_savepoint(thd, sv))
res= TRUE;
else if (((thd->variables.option_bits & OPTION_KEEP_LOG) ||
thd->transaction.all.modified_non_trans_table) &&
!thd->slave_thread)
push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN,
ER_WARNING_NOT_COMPLETE_ROLLBACK,
ER(ER_WARNING_NOT_COMPLETE_ROLLBACK));
thd->transaction.savepoints= sv;
/*
Release metadata locks that were acquired during this savepoint unit
unless binlogging is on. Releasing locks with binlogging on can break
replication as it allows other connections to drop these tables before
rollback to savepoint is written to the binlog.
*/
bool binlog_on= mysql_bin_log.is_open() && thd->variables.sql_log_bin;
if (!res && !binlog_on)
thd->mdl_context.rollback_to_savepoint(sv->mdl_savepoint);
DBUG_RETURN(test(res));
}
/**
Remove the named savepoint from the set of savepoints of
the current transaction.
@note No commit or rollback occurs. It is an error if the
savepoint does not exist.
@param thd Current thread
@param name Savepoint name
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_release_savepoint(THD *thd, LEX_STRING name)
{
int res= FALSE;
SAVEPOINT *sv= *find_savepoint(thd, name);
DBUG_ENTER("trans_release_savepoint");
if (sv == NULL)
{
my_error(ER_SP_DOES_NOT_EXIST, MYF(0), "SAVEPOINT", name.str);
DBUG_RETURN(TRUE);
}
if (ha_release_savepoint(thd, sv))
res= TRUE;
thd->transaction.savepoints= sv->prev;
DBUG_RETURN(test(res));
}
/**
Starts an XA transaction with the given xid value.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_xa_start(THD *thd)
{
enum xa_states xa_state= thd->transaction.xid_state.xa_state;
DBUG_ENTER("trans_xa_start");
if (xa_state == XA_IDLE && thd->lex->xa_opt == XA_RESUME)
{
bool not_equal= !thd->transaction.xid_state.xid.eq(thd->lex->xid);
if (not_equal)
my_error(ER_XAER_NOTA, MYF(0));
else
thd->transaction.xid_state.xa_state= XA_ACTIVE;
DBUG_RETURN(not_equal);
}
/* TODO: JOIN is not supported yet. */
if (thd->lex->xa_opt != XA_NONE)
my_error(ER_XAER_INVAL, MYF(0));
else if (xa_state != XA_NOTR)
my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
else if (thd->locked_tables_mode || thd->in_active_multi_stmt_transaction())
my_error(ER_XAER_OUTSIDE, MYF(0));
else if (xid_cache_search(thd->lex->xid))
my_error(ER_XAER_DUPID, MYF(0));
else if (!trans_begin(thd))
{
DBUG_ASSERT(thd->transaction.xid_state.xid.is_null());
thd->transaction.xid_state.xa_state= XA_ACTIVE;
thd->transaction.xid_state.rm_error= 0;
thd->transaction.xid_state.xid.set(thd->lex->xid);
xid_cache_insert(&thd->transaction.xid_state);
DBUG_RETURN(FALSE);
}
DBUG_RETURN(TRUE);
}
/**
Put a XA transaction in the IDLE state.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_xa_end(THD *thd)
{
DBUG_ENTER("trans_xa_end");
/* TODO: SUSPEND and FOR MIGRATE are not supported yet. */
if (thd->lex->xa_opt != XA_NONE)
my_error(ER_XAER_INVAL, MYF(0));
else if (thd->transaction.xid_state.xa_state != XA_ACTIVE)
my_error(ER_XAER_RMFAIL, MYF(0),
xa_state_names[thd->transaction.xid_state.xa_state]);
else if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
my_error(ER_XAER_NOTA, MYF(0));
else if (!xa_trans_rolled_back(&thd->transaction.xid_state))
thd->transaction.xid_state.xa_state= XA_IDLE;
DBUG_RETURN(thd->is_error() ||
thd->transaction.xid_state.xa_state != XA_IDLE);
}
/**
Put a XA transaction in the PREPARED state.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_xa_prepare(THD *thd)
{
DBUG_ENTER("trans_xa_prepare");
if (thd->transaction.xid_state.xa_state != XA_IDLE)
my_error(ER_XAER_RMFAIL, MYF(0),
xa_state_names[thd->transaction.xid_state.xa_state]);
else if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
my_error(ER_XAER_NOTA, MYF(0));
else if (ha_prepare(thd))
{
xid_cache_delete(&thd->transaction.xid_state);
thd->transaction.xid_state.xa_state= XA_NOTR;
my_error(ER_XA_RBROLLBACK, MYF(0));
}
else
thd->transaction.xid_state.xa_state= XA_PREPARED;
DBUG_RETURN(thd->is_error() ||
thd->transaction.xid_state.xa_state != XA_PREPARED);
}
/**
Commit and terminate the a XA transaction.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_xa_commit(THD *thd)
{
bool res= TRUE;
enum xa_states xa_state= thd->transaction.xid_state.xa_state;
DBUG_ENTER("trans_xa_commit");
if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
{
XID_STATE *xs= xid_cache_search(thd->lex->xid);
res= !xs || xs->in_thd;
if (res)
my_error(ER_XAER_NOTA, MYF(0));
else
{
res= xa_trans_rolled_back(xs);
ha_commit_or_rollback_by_xid(thd->lex->xid, !res);
xid_cache_delete(xs);
}
DBUG_RETURN(res);
}
if (xa_trans_rolled_back(&thd->transaction.xid_state))
{
if ((res= test(ha_rollback_trans(thd, TRUE))))
my_error(ER_XAER_RMERR, MYF(0));
}
else if (xa_state == XA_IDLE && thd->lex->xa_opt == XA_ONE_PHASE)
{
int r= ha_commit_trans(thd, TRUE);
if ((res= test(r)))
my_error(r == 1 ? ER_XA_RBROLLBACK : ER_XAER_RMERR, MYF(0));
}
else if (xa_state == XA_PREPARED && thd->lex->xa_opt == XA_NONE)
{
MDL_request mdl_request;
/*
Acquire metadata lock which will ensure that COMMIT is blocked
by active FLUSH TABLES WITH READ LOCK (and vice versa COMMIT in
progress blocks FTWRL).
We allow FLUSHer to COMMIT; we assume FLUSHer knows what it does.
*/
mdl_request.init(MDL_key::COMMIT, "", "", MDL_INTENTION_EXCLUSIVE,
MDL_TRANSACTION);
if (thd->mdl_context.acquire_lock(&mdl_request,
thd->variables.lock_wait_timeout))
{
ha_rollback_trans(thd, TRUE);
my_error(ER_XAER_RMERR, MYF(0));
}
else
{
DEBUG_SYNC(thd, "trans_xa_commit_after_acquire_commit_lock");
res= test(ha_commit_one_phase(thd, 1));
if (res)
my_error(ER_XAER_RMERR, MYF(0));
}
}
else
{
my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
DBUG_RETURN(TRUE);
}
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
xid_cache_delete(&thd->transaction.xid_state);
thd->transaction.xid_state.xa_state= XA_NOTR;
DBUG_RETURN(res);
}
/**
Roll back and terminate a XA transaction.
@param thd Current thread
@retval FALSE Success
@retval TRUE Failure
*/
bool trans_xa_rollback(THD *thd)
{
bool res= TRUE;
enum xa_states xa_state= thd->transaction.xid_state.xa_state;
DBUG_ENTER("trans_xa_rollback");
if (!thd->transaction.xid_state.xid.eq(thd->lex->xid))
{
XID_STATE *xs= xid_cache_search(thd->lex->xid);
if (!xs || xs->in_thd)
my_error(ER_XAER_NOTA, MYF(0));
else
{
xa_trans_rolled_back(xs);
ha_commit_or_rollback_by_xid(thd->lex->xid, 0);
xid_cache_delete(xs);
}
DBUG_RETURN(thd->stmt_da->is_error());
}
if (xa_state != XA_IDLE && xa_state != XA_PREPARED && xa_state != XA_ROLLBACK_ONLY)
{
my_error(ER_XAER_RMFAIL, MYF(0), xa_state_names[xa_state]);
DBUG_RETURN(TRUE);
}
/*
Resource Manager error is meaningless at this point, as we perform
explicit rollback request by user. We must reset rm_error before
calling ha_rollback(), so thd->transaction.xid structure gets reset
by ha_rollback()/THD::transaction::cleanup().
*/
thd->transaction.xid_state.rm_error= 0;
if ((res= test(ha_rollback_trans(thd, TRUE))))
my_error(ER_XAER_RMERR, MYF(0));
thd->variables.option_bits&= ~(OPTION_BEGIN | OPTION_KEEP_LOG);
thd->transaction.all.modified_non_trans_table= FALSE;
thd->server_status&= ~SERVER_STATUS_IN_TRANS;
xid_cache_delete(&thd->transaction.xid_state);
thd->transaction.xid_state.xa_state= XA_NOTR;
DBUG_RETURN(res);
}