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MDEV-7668: Intermediate master groups CREATE TEMPORARY with INSERT, causing parallel replication failure

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[This commit cherry-picked to be able to merge MDEV-7936, of which it
is a pre-requisite, into both 10.0 and 10.1.]

Parallel replication depends on locking (table locks, row locks, etc.) to
prevent two conflicting transactions from running and committing in parallel.
But temporary tables are designed to be visible only to one thread, and have
no such locking.

In the concrete issue, an intermediate master could commit a CREATE TEMPORARY
TABLE in the same group commit as in INSERT into that table. Thus, a
lower-level master could attempt to run them in parallel and get an error.

More generally, we need protection from parallel replication trying to run
transactions in parallel that access a common temporary table.

This patch simply causes use of a temporary table from parallel replication
to wait for all previous transactions to commit, serialising the replication
at that point.

(A more fine-grained locking could be added later, possibly. However,
using temporary tables in statement-based replication is in any case
normally undesirable; for example a restart of the server will lose
temporary tables and can break replication).

Note that row-based replication is not affected, as it does not do any
temporary tables on the slave-side.

This patch also cleans up the locking around protecting the list of
temporary tables in Relay_log_info. This used to take the
rli->data_lock at the end of every statement, which is very bad for
concurrency. With this patch, the lock is not taken unless temporary
tables (with statement-based binlogging) are in use on the slave.
This commit is contained in:
Kristian Nielsen
2015-03-09 13:06:32 +01:00
parent 15a2b5aab1
commit c47fe0e9db
4 changed files with 192 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

56
sql/sql_base.cc
View File

@ -661,20 +661,23 @@ static void mark_temp_tables_as_free_for_reuse(THD *thd)
DBUG_VOID_RETURN;
}
thd->lock_temporary_tables();
for (TABLE *table= thd->temporary_tables ; table ; table= table->next)
if (thd->temporary_tables)
{
if ((table->query_id == thd->query_id) && ! table->open_by_handler)
mark_tmp_table_for_reuse(table);
}
thd->unlock_temporary_tables();
if (thd->rgi_slave)
{
/*
Temporary tables are shared with other by sql execution threads.
As a safety messure, clear the pointer to the common area.
*/
thd->temporary_tables= 0;
thd->lock_temporary_tables();
for (TABLE *table= thd->temporary_tables ; table ; table= table->next)
{
if ((table->query_id == thd->query_id) && ! table->open_by_handler)
mark_tmp_table_for_reuse(table);
}
thd->unlock_temporary_tables();
if (thd->rgi_slave)
{
/*
Temporary tables are shared with other by sql execution threads.
As a safety messure, clear the pointer to the common area.
*/
thd->temporary_tables= 0;
}
}
DBUG_VOID_RETURN;
}
@ -5586,6 +5589,14 @@ TABLE *open_table_uncached(THD *thd, handlerton *hton,
(uint) thd->variables.server_id,
(ulong) thd->variables.pseudo_thread_id));
if (add_to_temporary_tables_list)
{
/* Temporary tables are not safe for parallel replication. */
if (thd->rgi_slave && thd->rgi_slave->is_parallel_exec &&
thd->wait_for_prior_commit())
return NULL;
}
/* Create the cache_key for temporary tables */
key_length= create_tmp_table_def_key(thd, cache_key, db, table_name);
@ -5822,6 +5833,25 @@ bool open_temporary_table(THD *thd, TABLE_LIST *tl)
DBUG_RETURN(FALSE);
}
/*
Temporary tables are not safe for parallel replication. They were
designed to be visible to one thread only, so have no table locking.
Thus there is no protection against two conflicting transactions
committing in parallel and things like that.
So for now, anything that uses temporary tables will be serialised
with anything before it, when using parallel replication.
ToDo: We might be able to introduce a reference count or something
on temp tables, and have slave worker threads wait for it to reach
zero before being allowed to use the temp table. Might not be worth
it though, as statement-based replication using temporary tables is
in any case rather fragile.
*/
if (thd->rgi_slave && thd->rgi_slave->is_parallel_exec &&
thd->wait_for_prior_commit())
DBUG_RETURN(true);
#ifdef WITH_PARTITION_STORAGE_ENGINE
if (tl->partition_names)
{