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Fix for bug #55273 "FLUSH TABLE tm WITH READ LOCK for Merge

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table causes assert failure".

Attempting to use FLUSH TABLE table_list WITH READ LOCK
statement for a MERGE table led to an assertion failure if
one of its children was not present in the list of tables
to be flushed. The problem was not visible in non-debug builds.

The assertion failure was caused by the fact that in such
situations FLUSH TABLES table_list WITH READ LOCK implementation
tried to use (e.g. lock) such child tables without acquiring
metadata lock on them. This happened because when opening tables
we assumed metadata locks on all tables were already acquired
earlier during statement execution and a such assumption was
false for MERGE children.

This patch fixes the problem by ensuring at open_tables() time
that we try to acquire metadata locks on all tables to be opened. 
For normal tables such requests are satisfied instantly since
locks are already acquired for them. For MERGE children metadata
locks are acquired in normal fashion.

Note that FLUSH TABLES merge_table WITH READ LOCK will lock for
read both the MERGE table and its children but will flush only 
the MERGE table. To flush children one has to mention them in table
list explicitly. This is expected behavior and it is consistent with
usage patterns for this statement (e.g. in mysqlhotcopy script).
This commit is contained in:
Dmitry Lenev
2010-09-09 18:29:14 +04:00
parent 51a3375c98
commit 3326614df1
6 changed files with 117 additions and 21 deletions
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50
mysql-test/r/flush.result
View File

@ -373,3 +373,53 @@ commit;
# --> connection con2
# --> connection default
drop table t1;
#
# Test for bug #55273 "FLUSH TABLE tm WITH READ LOCK for Merge table
# causes assert failure".
#
drop table if exists t1, t2, tm;
create table t1 (i int);
create table t2 (i int);
create table tm (i int) engine=merge union=(t1, t2);
insert into t1 values (1), (2);
insert into t2 values (3), (4);
# The below statement should succeed and lock merge
# table for read. Only merge table gets flushed and
# not underlying tables.
flush tables tm with read lock;
select * from tm;
i
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# Check that underlying tables are locked.
select * from t1;
i
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select * from t2;
i
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unlock tables;
# This statement should succeed as well and flush
# all tables in the list.
flush tables tm, t1, t2 with read lock;
select * from tm;
i
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# Naturally, underlying tables should be locked in this case too.
select * from t1;
i
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select * from t2;
i
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unlock tables;
drop tables tm, t1, t2;