On Mon, Feb 1, 2010 at 4:51 PM, Cui Shijun <rancp...@gmail.com> 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
