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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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49
sql/sql_base.cc
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@ -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;
@ -600,24 +600,43 @@ bool flush_tables(THD *thd, flush_tables_type flag)
else
{
/*
HA_OPEN_FOR_FLUSH is used to allow us to open the table even if
TABLE_SHARE::incompatible_version is set. It also will tell
SEQUENCE engine that we don't have to read the sequence information
(which may cause deadlocks with concurrently running ALTER TABLE or
ALTER SEQUENCE) as we will close the table at once.
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.
*/
if (!open_table_from_share(thd, share, &empty_clex_str,
HA_OPEN_KEYFILE, 0,
HA_OPEN_FOR_ALTER | HA_OPEN_FOR_FLUSH,
tmp_table, FALSE,
NULL))
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))
{
(void) tmp_table->file->extra(HA_EXTRA_FLUSH);
/*
We don't put the table into the TDC as the table was not fully
opened (we didn't open triggers)
HA_OPEN_FOR_FLUSH is used to allow us to open the table even if
TABLE_SHARE::incompatible_version is set. It also will tell
SEQUENCE engine that we don't have to read the sequence information
(which may cause deadlocks with concurrently running ALTER TABLE or
ALTER SEQUENCE) as we will close the table at once.
*/
closefrm(tmp_table);
if (!open_table_from_share(thd, share, &empty_clex_str,
HA_OPEN_KEYFILE, 0,
HA_OPEN_FOR_ALTER | HA_OPEN_FOR_FLUSH,
tmp_table, FALSE,
NULL))
{
(void) tmp_table->file->extra(HA_EXTRA_FLUSH);
/*
We don't put the table into the TDC as the table was not fully
opened (we didn't open triggers)
*/
closefrm(tmp_table);
}
thd->mdl_context.release_lock(mdl_request.ticket);
}
}
tdc_release_share(share);