Well they've just provided the logic, you need to run that as per your situation. Experiences have not been shared. On 01/04/16 18:06, Jean Weisbuch wrote:
As a side note, the documentation for the engine independent table statistics isn't very complete : - Is there a reason not to activate it and what are the possible downsides of its activation - How much could it slow down an ANALYZE and possibly other operations? - There are no practical examples except on the histogram-based stats page - There are no other mention than a link to the KB page of the histogram-based stats on the KB page.
Some of these slides could be re-used for the documentation I think : https://www.slideshare.net/mobile/SergeyPetrunya/mariadb-engine-independent-...
---- dE wrote ----
Humm.. thanks for clarifying that!
On 01/04/16 03:20, Sergei Golubchik wrote:
Hi, dE!
On Jan 02, dE wrote:
Hi! I was playing around with indexes after we faced problems with mariadb choosing the wrong index because of high average value group size.
So I created a table with 4 text columns and indexed the 4th
column with > >> a prefix length of 1. > >> > >> Following are the stats in brief -- > >> > >> The index has 35 unique values > >> There are around 1040000 rows in total. > >> this will give an average value group size of 29714 > >> Cardinality is calculated as <no. of records in the index>/<average size > >> of value groups>, thus it's value must be 35 > >> > >> BUT from show indexes, it's value is shown as 72 > >> (innodb_stats_persistent_sample_pages = 9999999). > > It's because InnoDB lies about the cardinality. It reports twice the > > actual value to the server. If MyISAM would report the cardinality as > > 36, InnoDB will say it's 72. > > > > You can enable the Engine Independent Table Statistics in MariaDB: > > https://mariadb.com/kb/en/mariadb/engine-independent-table-statistics/ <https://mariadb.com/kb/en/mariadb/engine-independent-table-statistics/%0D>; > > This will show the correct value. > > > > Regards, > > Sergei > > Chief Architect MariaDB > > and security@mariadb.org <mailto:security@mariadb.org> > > > _______________________________________________ > Mailing list: https://launchpad.net/~maria-discuss <https://launchpad.net/%7Emaria-discuss%0D>; > Post to : maria-discuss@lists.launchpad.net <mailto:maria-discuss@lists.launchpad.net> > Unsubscribe : https://launchpad.net/~maria-discuss <https://launchpad.net/%7Emaria-discuss%0D>; > More help : https://help.launchpad.net/ListHelp
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