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Bug#43230: SELECT ... FOR UPDATE can hang with FLUSH TABLES WITH READ LOCK indefinitely

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The problem is that a SELECT .. FOR UPDATE statement might open
a table and later wait for a impeding global read lock without
noticing whether it is holding a table that is being waited upon
the the flush phase of the process that took the global read
lock.

The same problem also affected the following statements:

LOCK TABLES .. WRITE
UPDATE .. SET (update and multi-table update)
TRUNCATE TABLE ..
LOAD DATA ..

The solution is to make the above statements wait for a impending
global read lock before opening the tables. If there is no
impending global read lock, the statement raises a temporary
protection against global read locks and progresses smoothly
towards completion.

Important notice: the patch does not try to address all possible
cases, only those which are common and can be fixed unintrusively
enough for 5.0.
This commit is contained in:
Davi Arnaut
2009-04-03 16:11:54 -03:00
parent 668d988c71
commit aebaf079d1
6 changed files with 231 additions and 2 deletions
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16
sql/sql_lex.h
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@ -1176,6 +1176,22 @@ typedef struct st_lex : public Query_tables_list
bool escape_used;
/*
Special case for SELECT .. FOR UPDATE and LOCK TABLES .. WRITE.
Protect from a impending GRL as otherwise the thread might deadlock
if it starts waiting for the GRL in mysql_lock_tables.
The protection is needed because there is a race between setting
the global read lock and waiting for all open tables to be closed.
The problem is a circular wait where a thread holding "old" open
tables will wait for the global read lock to be released while the
thread holding the global read lock will wait for all "old" open
tables to be closed -- the flush part of flush tables with read
lock.
*/
bool protect_against_global_read_lock;
st_lex();
virtual ~st_lex()