How many rows before the GROUP BY? Group by is, in effect a sorting process.. perhaps that contains enough data to justify going to disk.
What is the value of the variable sort_buffer_size? show variables like '%sort%'; - md On Thu, Sep 9, 2010 at 3:04 PM, Phil <freedc....@gmail.com> wrote: > On average it would be between 10 and 40, certainly no more than 100. > > > On Thu, Sep 9, 2010 at 2:57 PM, Michael Dykman <mdyk...@gmail.com> wrote: >> >> The filesort is probably necessary because of the number of rows in >> the result set to be ordered. How many rows do you get out of this >> query? >> >> - michael dykman >> >> On Thu, Sep 9, 2010 at 1:53 PM, Phil <freedc....@gmail.com> wrote: >> > I wonder if anyone could help with a query which I've been unable to >> > prevent >> > from using a filesort. Might be something obvious I'm overlooking! >> > >> > I have a table which tracks milestones in distributed computing projects >> > >> > Create Table: CREATE TABLE `boinc_milestone` ( >> > `proj` char(6) NOT NULL, >> > `id` int(11) NOT NULL, >> > `stat_date` date NOT NULL DEFAULT '0000-00-00', >> > `milestone_type` char(1) NOT NULL DEFAULT '0', >> > `milestone` double NOT NULL DEFAULT '0', >> > `cpid` varchar(32) DEFAULT NULL, >> > `team` int(11) DEFAULT NULL, >> > PRIMARY KEY (`proj`,`id`,`stat_date`,`milestone`), >> > KEY `two` (`proj`,`stat_date`,`id`,`milestone`), >> > KEY `cpid` (`cpid`,`proj`,`id`,`stat_date`,`milestone`), >> > KEY `team` (`proj`,`team`,`id`,`stat_date`,`milestone`) >> > ) ENGINE=MyISAM DEFAULT CHARSET=latin1 >> > >> > These are added to on a daily basis as users pass the various credit >> > milestones so for instance you can end up with rows for >> > 1000,5000,10000,50000,1000000 etc on different dates as time goes on. >> > >> > Now on one page for display I want to show the latest milestone for each >> > project for a particular cpid. The query I use is as follows: >> > >> > select a.proj,a.id,max(stat_date),max(a.milestone) as >> > milestone,b.description >> > from boinc_milestone a join boinc_projects b on a.proj = b.proj >> > where cpid = '$cpid' >> > group by proj >> > order by stat_date desc >> > >> > The order by causes the filesort and I can't find an easy way around it. >> > >> > mysql> explain select a.proj,a.id,max(stat_date),max(a.milestone) as >> > milestone,b.description from boinc_milestone a join boinc_projects b on >> > a.proj = b.proj where cpid = 'XXX' group by proj order by stat_date\G >> > *************************** 1. row *************************** >> > id: 1 >> > select_type: SIMPLE >> > table: a >> > type: ref >> > possible_keys: PRIMARY,two,cpid,team >> > key: cpid >> > key_len: 35 >> > ref: const >> > rows: 1 >> > Extra: Using where; Using index; Using temporary; Using filesort >> > *************************** 2. row *************************** >> > id: 1 >> > select_type: SIMPLE >> > table: b >> > type: eq_ref >> > possible_keys: PRIMARY >> > key: PRIMARY >> > key_len: 10 >> > ref: stats.a.proj >> > rows: 1 >> > Extra: Using where >> > 2 rows in set (0.00 sec) >> > >> > I could just remove the order by altogether and perform the sort in php >> > afterwards I guess but any other ideas? >> > >> > Thanks >> > >> > Phil >> > >> > -- >> > Distributed Computing stats >> > http://stats.free-dc.org >> > >> >> >> >> -- >> - michael dykman >> - mdyk...@gmail.com >> >> May the Source be with you. > > > > -- > Distributed Computing stats > http://stats.free-dc.org > -- - michael dykman - mdyk...@gmail.com May the Source be with you. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org