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From:Wagner Bianchi Date:February 1 2010 4:44pm
Subject:Re: Is table_open_cache a private cache of a session?
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Is FD_SETSIZE regards to an open_file_limit?

WB

2010/2/1 Cui Shijun <rancpine@stripped>

>  Got your idea.
>  Thank you very much. Now I know how table cache works :-)
>
>  For the bug, yes, it's related to the value of FD_SETSIZE, which is
> limited to 1024 at my RedHat box.
> Maybe I should update it to a suitable value.
>
> 2010/2/2 Johan De Meersman <vegivamp@stripped>:
>  >
> > On Mon, Feb 1, 2010 at 4:51 PM, Cui Shijun <rancpine@stripped> wrote:
> >>
> >> I'm also confused by the difference & relationship between "open
> >> table" and "open file descriptor" by the table cache.
> >
> > "open table" is a MySQL concept. "Open file descriptor" is an OS concept.
> A
> > single table (MyISAM) consists of three files: the .frm (description),
> the
> > .MYD (data) and the .MYI (indices). Thus, a single open table can
> correspond
> > to multiple open files. Additionally, temp tables, sortfiles and whatnot
> > also consume file descriptors.
> >
> >>
> >>  As far as I understand, when a thread ask the global cache for a table:
> >> * if the table is opened before and currently not used by other
> >> thread, the request thread will get this table
> >
> > "and *there is a cache entry that* is currently not used*" - multiple
> > entries can exist for the same table.
> >
> >>
> >> * if no table in table cache is available( currently used by other
> >> thread, or not opened before ), the request thread will open this
> >> table
> >
> > The thread will get a new cache object that opens that table, yes.
> >
> >>
> >>  Once open a table, mysql *might?( I'm not sure )* open a file
> >> descriptor corresponding to the data file of the table. In that case,
> >> when the number of  table opened simultaneously goes too big, mysql
> >> will use too much file descriptors and then hit the bug 48929.
> >>
> >>  Your experience( "I've had one occurrence where it grew to 26.000
> >> open tables" ) seems to show there must be something wrong with my
> >> understanding, Hmm...  :-(
> >
> > I just skimmed over it, but the bug seem related specifically to InnoDB,
> and
> > to a highly specific file descriptor number being equal to some form of
> > hardcoded limit - maybe different OSes or linux distro's have different
> > values for said limit, or maybe it only occurs under specific conditions.
> >
> >
> >
> > --
> > Bier met grenadyn
> > Is als mosterd by den wyn
> > Sy die't drinkt, is eene kwezel
> > Hy die't drinkt, is ras een ezel
> >
>
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Thread
Is table_open_cache a private cache of a session?Cui Shijun1 Feb
  • Re: Is table_open_cache a private cache of a session?Johan De Meersman1 Feb
    • Re: Is table_open_cache a private cache of a session?Cui Shijun1 Feb
      • Re: Is table_open_cache a private cache of a session?Johan De Meersman1 Feb
        • Re: Is table_open_cache a private cache of a session?Cui Shijun1 Feb
          • Re: Is table_open_cache a private cache of a session?Wagner Bianchi1 Feb
            • Re: Is table_open_cache a private cache of a session?Wagner Bianchi1 Feb
              • Re: Is table_open_cache a private cache of a session?Cui Shijun1 Feb