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Bug#32395 Alter table under a impending global read lock causes a server crash

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The problem is that some DDL statements (ALTER TABLE, CREATE
TRIGGER, FLUSH TABLES, ...) when under LOCK TABLES need to
momentarily drop the lock, reopen the table and grab the write
lock again (using reopen_tables). When grabbing the lock again,
reopen_tables doesn't pass a flag to mysql_lock_tables in
order to ignore the impending global read lock, which causes a
assertion because LOCK_open is being hold. Also dropping the
lock must not signal to any threads that the table has been
relinquished (related to the locking/flushing protocol).

The solution is to correct the way the table is reopenned
and the locks grabbed. When reopening the table and under
LOCK TABLES, the table version should be set to 0 so other
threads have to wait for the table. When grabbing the lock,
any other flush should be ignored because it's theoretically
a atomic operation. The chosen solution also fixes a potential
discrepancy between binlog and GRL (global read lock) because
table placeholders were being ignored, now a FLUSH TABLES WITH
READ LOCK will properly for table with open placeholders.

It's also important to mention that this patch doesn't fix
a potential deadlock if one uses two GRLs under LOCK TABLES
concurrently.
This commit is contained in:
davi@mysql.com/endora.local
2007-12-12 19:44:14 -02:00
parent 8651e9dddf
commit 137e90ed55
11 changed files with 206 additions and 41 deletions
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14
mysql-test/r/trigger_notembedded.result
View File

@ -448,4 +448,18 @@ DROP TABLE t1;
DROP DATABASE mysqltest_db1;
USE test;
End of 5.0 tests.
drop table if exists t1;
create table t1 (i int);
connection: default
lock tables t1 write;
connection: flush
flush tables with read lock;;
connection: default
create trigger t1_bi before insert on t1 for each row begin end;
unlock tables;
connection: flush
unlock tables;
select * from t1;
i
drop table t1;
End of 5.1 tests.