Re: scanning 2 rows slow index fast 26GB MyISAM

[Bryan Heitman]

My mistake!  Here you go:
CREATE TABLE `matrix` (
 `WordID` int(11) unsigned NOT NULL default '0',
 `LocationID` int(11) unsigned NOT NULL default '0',
 `Position` enum('Body','From','Subject','To','Mailbox','File') NOT NULL 
default 'Body',
 `times` int(11) unsigned NOT NULL default '0',
 `MyOrder` int(11) unsigned NOT NULL default '0',
 `AccountID` int(11) unsigned NOT NULL default '0',
 `date` timestamp(19) NOT NULL,
 KEY `myKey` (`AccountID`,`WordID`,`Position`,`date`),
 KEY `myKey2` (`LocationID`)
) TYPE=MyISAM MAX_ROWS=1000000000 AVG_ROW_LENGTH=300 DATA 
DIRECTORY='/home/imap/fuse3.disk2/SQL/search/'

----- Original Message ----- 
From: "Sergio Salvi" <[EMAIL PROTECTED]>
To: "Bryan Heitman" <[EMAIL PROTECTED]>
Cc: <mysql@lists.mysql.com>
Sent: Thursday, December 23, 2004 10:08 AM
Subject: Re: scanning 2 rows slow index fast 26GB MyISAM


Bryan,
Can you send the output of "show create table matrix"? You've just sent
the "location" table output, but your select command refers to a table
called "matrix".
[]s,
Sergio.
On Wed, 22 Dec 2004, Bryan Heitman wrote:
I am experiencing extreme slowness performing a query in which 2 rows are
returned hanging in the "sending data" status.
Performing an index only query such as SELECT COUNT(*) is extremely quick 
so
I know the only extra step is retrieving the data from the MYD.

I am looking for thoughts on why this is slow and what can be done to 
speed
it up.  I find it unusual why it would take this long to simply grab 2 
rows
from the MYD.  vmstat reports high reads and strace confirms pread()'s on
the MYD file.

The only abnormality is my  table size MYD is 26 gig and my MYI is about 
30
gig.

Test system details, tests were performed with no load.
System: Redhat Linux 2.4.28
Mysql: tested on versions 4.0.22 and latest 4.1 tree
IDE (WD 2500 JB 8 mb buff) disk1 used for MYD (written contiguously at
beginning of disk)
IDE (WD 2500 JB 8 mb buff) disk2 used for MYI
dual xeon 2.4ghz
1gb ddr266 mem
Here are query tests & detail below:
mysql> select count(*) from matrix where accountid = 11 and wordid = 72 
and
position = 'Body' and date > now() - interval 10 day;
+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set (0.06 sec)

mysql> select locationid from matrix where accountid = 11 and wordid = 72
and position = 'Body' and date > now() - interval 10 day;
+------------+
| locationid |
+------------+
|      47932 |
|      29571 |
+------------+
2 rows in set (5 min 35.93 sec)
mysql> explain select locationid from matrix where accountid = 11 and 
wordid
= 71 and position = 'Body' and date > now() - interval 10 day;
+--------+------+---------------+-------+---------+-------------------+-------+-------------+
| table  | type | possible_keys | key   | key_len | ref               | 
rows
| Extra       |
+--------+------+---------------+-------+---------+-------------------+-------+-------------+
| matrix | ref  | myKey         | myKey |       9 | const,const,const |
56909 | Using where |
+--------+------+---------------+-------+---------+-------------------+-------+-------------+

CREATE TABLE `location` (
  `LocationID` int(11) unsigned NOT NULL auto_increment,
  `ImapUID` int(11) unsigned NOT NULL default '0',
  `AccountID` int(11) unsigned NOT NULL default '0',
  `Date` timestamp(19) NOT NULL,
  `FromWho` tinyblob,
  `Subject` tinyblob,
  `SentTo` tinyblob,
  `mailbox` varchar(255) default NULL,
  `body` longblob,
  PRIMARY KEY  (`LocationID`),
  KEY `myKey` (`LocationID`,`AccountID`,`Date`)
) TYPE=MyISAM MAX_ROWS=1000000000 AVG_ROW_LENGTH=300 DATA
DIRECTORY='/home/SQL/' INDEX DIRECTORY='/home/SQL/'




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