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MDEV-28897 Wrong table.get_ref_count() upon concurrent truncate and backup stage operation

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The issue was that flush_tables() didn't take a MDL lock on cached
TABLE_SHARE before calling open_table() to do a HA_EXTRA_FLUSH call.
Most engines seams to have no issue with it, but apparantly this conflicts
with InnoDB in 10.6 when using TRUNCATE

Fixed by taking a MDL lock before trying to open the table in
flush_tables().

There is no test case as it hard to repeat the scheduling that causes
the error. I did run the test case in MDEV-28897 to verify
that the bug is fixed.
This commit is contained in:
Monty
2022-06-28 15:57:41 +03:00
parent 02a313dc56
commit 5e40934d24
1 changed files with 34 additions and 15 deletions
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21
sql/sql_base.cc
View File

@ -515,7 +515,7 @@ public:
Sql_condition ** cond_hdl)
{
*cond_hdl= NULL;
if (sql_errno == ER_OPEN_AS_READONLY)
if (sql_errno == ER_OPEN_AS_READONLY || sql_errno == ER_LOCK_WAIT_TIMEOUT)
{
handled_errors++;
return TRUE;
@ -598,6 +598,23 @@ bool flush_tables(THD *thd, flush_tables_type flag)
tc_release_table(table);
}
else
{
/*
No free TABLE instances available. We have to open a new one.
Try to take a MDL lock to ensure we can open a new table instance.
If the lock fails, it means that some DDL operation or flush tables
with read lock is ongoing.
In this case we cannot sending the HA_EXTRA_FLUSH signal.
*/
MDL_request mdl_request;
MDL_REQUEST_INIT(&mdl_request, MDL_key::TABLE,
share->db.str,
share->table_name.str,
MDL_SHARED, MDL_EXPLICIT);
if (!thd->mdl_context.acquire_lock(&mdl_request, 0))
{
/*
HA_OPEN_FOR_FLUSH is used to allow us to open the table even if
@ -619,6 +636,8 @@ bool flush_tables(THD *thd, flush_tables_type flag)
*/
closefrm(tmp_table);
}
thd->mdl_context.release_lock(mdl_request.ticket);
}
}
tdc_release_share(share);
}