Details
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Type:
Bug
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Status: Closed
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Priority:
Major
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Resolution: Fixed
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
Description
Based on customer case, csc#250:
CREATE TABLE tbl (
id PRIMARY KEY,
key1 INT,
key2 INT,
KEY (key1),
KEY (key2) ) engine=innodb;
...
DELETE tbl FROM tbl WHERE key1=const1 AND key2=const2;
^^ this will delete fewer rows than it actually matches.
- Problem happens only with InnoDB (not with MyISAM)
- Setting "index_merge=off" fixes the problem.
- Using a non-multi-table-table DELETE statement fixes the problem.
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Re: Multi-table DELETE that uses innodb + index_merge/intersect may fail to delete rows
The cause of the problem is
- a multi-table DELETE attempts to use an index_merge/intersect +"Using index" to read rows.
= (for single-table DELETE, the problem doesnt show up, because index_merge/intersect is disabled) - "Using index" means that index_merge will read each column value from its index, and try to assemble a record from them (the record is needed to check the WHERE clause).
- the table is used in DELETE, so table->no_keyread==TRUE. opt_range.cc has this [ancient] code:
int QUICK_RANGE_SELECT::init_ror_merged_scan(bool reuse_handler)
{
...
if (!head->no_keyread)
....
I don't understand the reasoning behind it, but its result is that we will fail to call head->mark_columns_used_by_index(index). This didn't cause the problem up to version 5.2, because opt_range also used old "useless-stub" MRR, which had handler::read_multi_range_first(), which had a call to
table->mark_columns_used_by_index_no_reset(), which fixed things.
However, in 5.3's new MRR we have removed that (because it's generally not needed), and hence this bug.
Re: Multi-table DELETE that uses innodb + index_merge/intersect may fail to delete rows
However, if I just move the mark_columns_used_by_index() outside of the if-statement, I get this error with tests:
At line 287: query 'DELETE t1 FROM t1,t2 WHERE t1.c1=0 AND t1.c2=0' failed: 126: Incorrect key file for table './test/t1.MYI'; try to repair it
will need to investigate.
Re: Multi-table DELETE that uses innodb + index_merge/intersect may fail to delete rows
Fix pushed into MariaDB 5.3
Re: Multi-table DELETE that uses innodb + index_merge/intersect may fail to delete rows
Fix released in 5.5.25 and will be in 5.3.8 when it is out
Launchpad bug id: 1006164
Re: Multi-table DELETE that uses innodb + index_merge/intersect may fail to delete rows
Doesn't occur in MariaDB 5.2, occurs in 5.3 and 5.5