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MDEV-21953 deadlock between BACKUP STAGE BLOCK_COMMIT and parallel repl.

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The issue was:
T1, a parallel slave worker thread, is waiting for another worker thread to
commit. While waiting, it has the MDL_BACKUP_COMMIT lock.
T2, working for mariabackup, is doing BACKUP STAGE BLOCK_COMMIT and blocks
all commits.
This causes a deadlock as the thread T1 is waiting for can't commit.

Fixed by moving locking of MDL_BACKUP_COMMIT from ha_commit_trans() to
commit_one_phase_2()

Other things:
- Added a new argument to ha_comit_one_phase() to signal if the
  transaction was a write transaction.
- Ensured that ha_maria::implicit_commit() is always called under
  MDL_BACKUP_COMMIT. This code is not needed in 10.5
- Ensure that MDL_Request values 'type' and 'ticket' are always
  initialized. This makes it easier to check the state of the MDL_Request.
- Moved thd->store_globals() earlier in handle_rpl_parallel_thread() as
  thd->init_for_queries() could use a MDL that could crash if store_globals
  where not called.
- Don't call ha_enable_transactions() in THD::init_for_queries() as this
  is both slow (uses MDL locks) and not needed.
This commit is contained in:
Monty
2020-07-20 15:19:25 +03:00
parent c4d5b6b157
commit fc48c8ff4c
11 changed files with 210 additions and 59 deletions
Download Patch File Download Diff File Expand all files Collapse all files

117
sql/handler.cc
View File

@ -114,7 +114,7 @@ static TYPELIB known_extensions= {0,"known_exts", NULL, NULL};
uint known_extensions_id= 0;
static int commit_one_phase_2(THD *thd, bool all, THD_TRANS *trans,
bool is_real_trans);
bool is_real_trans, bool rw_trans);
static plugin_ref ha_default_plugin(THD *thd)
@ -133,6 +133,23 @@ static plugin_ref ha_default_tmp_plugin(THD *thd)
return ha_default_plugin(thd);
}
#if defined(WITH_ARIA_STORAGE_ENGINE) && MYSQL_VERSION_ID < 100500
void ha_maria_implicit_commit(THD *thd, bool new_trn)
{
if (ha_maria::has_active_transaction(thd))
{
int error;
MDL_request mdl_request;
mdl_request.init(MDL_key::BACKUP, "", "", MDL_BACKUP_COMMIT, MDL_EXPLICIT);
error= thd->mdl_context.acquire_lock(&mdl_request,
thd->variables.lock_wait_timeout);
ha_maria::implicit_commit(thd, new_trn);
if (!error)
thd->mdl_context.release_lock(mdl_request.ticket);
}
}
#endif
/** @brief
Return the default storage engine handlerton for thread
@ -1445,10 +1462,6 @@ int ha_commit_trans(THD *thd, bool all)
DBUG_RETURN(2);
}
#ifdef WITH_ARIA_STORAGE_ENGINE
ha_maria::implicit_commit(thd, TRUE);
#endif
if (!ha_info)
{
/*
@ -1462,7 +1475,9 @@ int ha_commit_trans(THD *thd, bool all)
wsrep_commit_empty(thd, all);
}
#endif /* WITH_WSREP */
DBUG_RETURN(0);
ha_maria_implicit_commit(thd, TRUE);
DBUG_RETURN(error);
}
DBUG_EXECUTE_IF("crash_commit_before", DBUG_SUICIDE(););
@ -1475,33 +1490,9 @@ int ha_commit_trans(THD *thd, bool all)
/* rw_trans is TRUE when we in a transaction changing data */
bool rw_trans= is_real_trans &&
(rw_ha_count > (thd->is_current_stmt_binlog_disabled()?0U:1U));
MDL_request mdl_request;
DBUG_PRINT("info", ("is_real_trans: %d rw_trans: %d rw_ha_count: %d",
is_real_trans, rw_trans, rw_ha_count));
if (rw_trans)
{
/*
Acquire a metadata lock which will ensure that COMMIT is blocked
by an active FLUSH TABLES WITH READ LOCK (and vice versa:
COMMIT in progress blocks FTWRL).
We allow the owner of FTWRL to COMMIT; we assume that it knows
what it does.
*/
mdl_request.init(MDL_key::BACKUP, "", "", MDL_BACKUP_COMMIT, MDL_EXPLICIT);
if (!WSREP(thd) &&
thd->mdl_context.acquire_lock(&mdl_request,
thd->variables.lock_wait_timeout))
{
ha_rollback_trans(thd, all);
DBUG_RETURN(1);
}
DEBUG_SYNC(thd, "ha_commit_trans_after_acquire_commit_lock");
}
if (rw_trans &&
opt_readonly &&
!(thd->security_ctx->master_access & SUPER_ACL) &&
@ -1541,7 +1532,7 @@ int ha_commit_trans(THD *thd, bool all)
// Here, the call will not commit inside InnoDB. It is only working
// around closing thd->transaction.stmt open by TR_table::open().
if (all)
commit_one_phase_2(thd, false, &thd->transaction.stmt, false);
commit_one_phase_2(thd, false, &thd->transaction.stmt, false, false);
}
}
#endif
@ -1561,7 +1552,7 @@ int ha_commit_trans(THD *thd, bool all)
goto wsrep_err;
}
#endif /* WITH_WSREP */
error= ha_commit_one_phase(thd, all);
error= ha_commit_one_phase(thd, all, rw_trans);
#ifdef WITH_WSREP
if (run_wsrep_hooks)
error= error || wsrep_after_commit(thd, all);
@ -1613,7 +1604,7 @@ int ha_commit_trans(THD *thd, bool all)
if (!is_real_trans)
{
error= commit_one_phase_2(thd, all, trans, is_real_trans);
error= commit_one_phase_2(thd, all, trans, is_real_trans, rw_trans);
goto done;
}
#ifdef WITH_WSREP
@ -1631,7 +1622,7 @@ int ha_commit_trans(THD *thd, bool all)
DEBUG_SYNC(thd, "ha_commit_trans_after_log_and_order");
DBUG_EXECUTE_IF("crash_commit_after_log", DBUG_SUICIDE(););
error= commit_one_phase_2(thd, all, trans, is_real_trans) ? 2 : 0;
error= commit_one_phase_2(thd, all, trans, is_real_trans, rw_trans) ? 2 : 0;
#ifdef WITH_WSREP
if (run_wsrep_hooks && (error || (error = wsrep_after_commit(thd, all))))
{
@ -1694,16 +1685,6 @@ err:
thd->rgi_slave->is_parallel_exec);
}
end:
if (rw_trans && mdl_request.ticket)
{
/*
We do not always immediately release transactional locks
after ha_commit_trans() (see uses of ha_enable_transaction()),
thus we release the commit blocker lock as soon as it's
not needed.
*/
thd->mdl_context.release_lock(mdl_request.ticket);
}
#ifdef WITH_WSREP
if (wsrep_is_active(thd) && is_real_trans && !error &&
(rw_ha_count == 0 || all) &&
@ -1719,6 +1700,7 @@ end:
/**
@note
This function does not care about global read lock. A caller should.
However backup locks are handled in commit_one_phase_2.
@param[in] all Is set in case of explicit commit
(COMMIT statement), or implicit commit
@ -1727,7 +1709,7 @@ end:
autocommit=1.
*/
int ha_commit_one_phase(THD *thd, bool all)
int ha_commit_one_phase(THD *thd, bool all, bool rw_trans)
{
THD_TRANS *trans=all ? &thd->transaction.all : &thd->transaction.stmt;
/*
@ -1753,20 +1735,50 @@ int ha_commit_one_phase(THD *thd, bool all)
if ((res= thd->wait_for_prior_commit()))
DBUG_RETURN(res);
}
res= commit_one_phase_2(thd, all, trans, is_real_trans);
res= commit_one_phase_2(thd, all, trans, is_real_trans, rw_trans);
DBUG_RETURN(res);
}
static int
commit_one_phase_2(THD *thd, bool all, THD_TRANS *trans, bool is_real_trans)
commit_one_phase_2(THD *thd, bool all, THD_TRANS *trans, bool is_real_trans,
bool rw_trans)
{
int error= 0;
uint count= 0;
Ha_trx_info *ha_info= trans->ha_list, *ha_info_next;
MDL_request mdl_request;
DBUG_ENTER("commit_one_phase_2");
if (is_real_trans)
DEBUG_SYNC(thd, "commit_one_phase_2");
if (rw_trans)
{
/*
Acquire a metadata lock which will ensure that COMMIT is blocked
by an active FLUSH TABLES WITH READ LOCK (and vice versa:
COMMIT in progress blocks FTWRL).
We allow the owner of FTWRL to COMMIT; we assume that it knows
what it does.
*/
mdl_request.init(MDL_key::BACKUP, "", "", MDL_BACKUP_COMMIT, MDL_EXPLICIT);
if (!WSREP(thd) &&
thd->mdl_context.acquire_lock(&mdl_request,
thd->variables.lock_wait_timeout))
{
my_error(ER_ERROR_DURING_COMMIT, MYF(0), 1);
ha_rollback_trans(thd, all);
DBUG_RETURN(1);
}
DEBUG_SYNC(thd, "ha_commit_trans_after_acquire_commit_lock");
}
#if defined(WITH_ARIA_STORAGE_ENGINE) && MYSQL_VERSION_ID < 100500
ha_maria::implicit_commit(thd, TRUE);
#endif
if (ha_info)
{
for (; ha_info; ha_info= ha_info_next)
@ -1795,6 +1807,17 @@ commit_one_phase_2(THD *thd, bool all, THD_TRANS *trans, bool is_real_trans)
#endif
}
}
if (mdl_request.ticket)
{
/*
We do not always immediately release transactional locks
after ha_commit_trans() (see uses of ha_enable_transaction()),
thus we release the commit blocker lock as soon as it's
not needed.
*/
thd->mdl_context.release_lock(mdl_request.ticket);
}
/* Free resources and perform other cleanup even for 'empty' transactions. */
if (is_real_trans)
{