maria-discuss team mailing list archive

[Sergey Vojtovich <svoj@xxxxxxxxxxx>]

Hi!

I think original question was about 5.5.

MySQL 5.6 has partitioned table cache, but rather to overcome the negative
scalability aspect of increasing number of concurrent connections.

No version of MariaDB has partitioned table cache. At least yet.

Regards,
Sergey

On Tue, Apr 21, 2015 at 10:43:05AM -0700, Justin Swanhart wrote:
> Hi,
> 
> Is that a MariaDB table_cache improvement?  MySQL 5.6 has partitioned table
> cache to overcome the negative scalability aspect of increasing table cache.
> 
> --Justin
> 
> On Tue, Apr 21, 2015 at 10:34 AM, Sergey Vojtovich <svoj@xxxxxxxxxxx> wrote:
> 
> > Hi!
> >
> > On Tue, Apr 21, 2015 at 10:11:12AM -0700, Justin Swanhart wrote:
> > > Hi,
> > >
> > > If a MyISAM table is not in the table_open_cache, it will be opened by
> > the
> > > query that needs the table.  To increase the chances of the table being
> > in
> > > the table_open_cache, increase the size to 4000 for a start (1/10 of your
> > > current open files).
> > Same applies to InnoDB tables, especially with low innodb_file_per_table
> > and
> > innodb_open_files. But MyISAM needs to open a 2x more files indeed.
> >
> > >
> > > Be careful though.  Increasing the table_open_cache increases the amount
> > of
> > > time it takes to search the table cache, as the search is linear through
> > > the structure that holds the table_cache.  It also increases the time
> > for a
> > > flush tables operation.
> > Table cache is doubly-linked list, but there is no table cache search as
> > such:
> > we either take front element or push front element. So increased
> > table_open_cache
> > doesn't have any negative effect on table cache performance. FLUSH TABLES
> > will be
> > slower indeed.
> >
> > To get best performance table_open_cache should be something like:
> > number of hot tables * average number of concurrent connections.
> >
> > >
> > > Also increase table_definition_cache.  This value is hash backed, so the
> > > performance impact of increasing it is minimal.  I would increase it to
> > > 40000 since you have 40000 open files.
> > A good value for table_definition_cache is number of hot tables + some
> > reserve
> > (e.g. 100).
> >
> > Regards,
> > Sergey
> >
> > >
> > > These value changes can be made online.
> > >
> > > On Tue, Apr 21, 2015 at 9:14 AM, Honza Horak <hhorak@xxxxxxxxxx> wrote:
> > >
> > > > On 04/21/2015 05:07 PM, Justin Swanhart wrote:
> > > >
> > > >> Hi,
> > > >>
> > > >> Are you using MyISAM or InnoDB?  What are the values of
> > > >> table_open_cache, table_definition_cache and innodb_open_files?
> > > >>
> > > >
> > > > It is a mixture of MyISAM and InnoDB, but we got complaints especially
> > > > about the MyISAM tables.
> > > >
> > > > Options table_open_cache, table_definition_cache have default values,
> > so
> > > > 400, innodb_open_files is changed to 128.
> > > >
> > > > Honza
> > > >
> > > >  --justin
> > > >>
> > > >> On Tue, Apr 21, 2015 at 6:26 AM, Honza Horak <hhorak@xxxxxxxxxx
> > > >> <mailto:hhorak@xxxxxxxxxx>> wrote:
> > > >>
> > > >>     Hey, with limited experiences with mariadb deployments, I'm
> > > >>     wondering how many open files by the mysqld daemon is still sane
> > > >>     (expected).
> > > >>
> > > >>     We have a customer that reports hundreds of thousands of open
> > files
> > > >>     with 600 connections (thread_pool_max_threads is used). Those
> > > >>     processes seem rather stalled, but files in the datadir are often
> > > >>     opened 40.000 times.
> > > >>
> > > >>     Is it even possible that one file is opened several times during
> > > >>     processing one query? Or does it mean there are ~40.000 queries
> > > >> running?
> > > >>
> > > >>     Version of MariaDB: 5.5.40
> > > >>
> > > >>     Honza
> > > >>
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