Comments on: ANALYZE: MyISAM vs Innodb

By: Dor

Dor — Fri, 27 Mar 2009 12:38:58 +0000

Hi peter,

Each one of the queries that are displayed in this page has a specific display format which includes the query itself, the result set (neatly separated with stripped lines) & the time it took to execute.

How did you do that?
I see this query-display-format in many developers websites.
It seems that you use an SQL tools for that.

Thanks in advance,
Dor.

By: Gunnar

Gunnar — Wed, 26 Nov 2008 08:13:03 +0000

Hi Peter,

I fully agree with you.
I’ve faced the same problem at a customer.

When the customer switched from MyISAM to InnoDb some queries that before took > 1 sec now took several minutes.
The reason we slightly wrong stats in the innodb analyse which made the optimizer create tabsolutely wrong query plans.

All these queries could be fixed with manually hinting with STRAIGHT_JOIN or FORCE INDEX.

But of course it would have been much nicer if the stats would be correct on inno.

Did you file a bug for this already?

By: peter

peter — Thu, 04 Sep 2008 17:32:05 +0000

StephaneC,

Well Analyze for Innodb can be helpful… It gives you cardinalities which are at least show the order of magnitude for cardinality which can help certain join queries.

The OPTIMIZE TABLE… this is good to have for Innodb in theory but in practice because this rebuilds the whole table it is most typically too slow to be useful. There are cases when OPTIMIZE takes weeks to complete. Plus because it builds indexes via “inserts” it does not really optimize things as well as it could. And the table will be read only for the whole duration

MySQL 5.1 Innodb plugin can build indexes faster but you need to do particular way of dump and reload to get benefit of this fast load.

By: StephaneC

StephaneC — Thu, 04 Sep 2008 08:52:53 +0000

So we can conclude from your tests that ANALYZE TABLE on InnoDB tables is useless. We’d better only use OPTIMIZE TABLE to defragment the tables (and this will also update index statistics as OPTIMIZE is mapped to ALTER TABLE).
Am I right or can we imagine situations where ANALYZE TABLE will be helpful with InnoDB ?

By: Julien

Julien — Thu, 04 Sep 2008 00:13:19 +0000

Wow !

You’ve made my day ! Thanks a lot for those informations/tests.