process wakeups
Steve Grubb
sgrubb at redhat.com
Tue Jul 15 15:28:59 UTC 2008
On Tuesday 15 July 2008 11:15:56 Bill Crawford wrote:
> > One of the worst that I've found that's not on the list is mysqld. It has
> > 2 threads that just never stop.
>
> I see about 1 wakeup per second from mysqld (it's currently idle,
> though). What are you seeing there?
ps -ef | grep sql
root 2227 1 0 07:41 ?
00:00:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid
mysql 2286 2227 0 07:41 ?
00:00:12 /usr/libexec/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --skip-external-locking --socket=/var/lib/mysql/mysql.sock
ls /proc/2286/task/
2286 2296 2297 2298 2299 2301 2304 2308 2309 2312 2460
then strace them.
strace -p 2301
Process 2301 attached - interrupt to quit
select(0, NULL, NULL, NULL, {0, 78000}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {1, 0}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {1, 0}^C <unfinished ...>
...this is after about 5 seconds. This thread just never gets quiet and is
constantly churning. My system is idle too with nothing being added or
deleted or read from the database.
strace -p 2304
Process 2304 attached - interrupt to quit
select(0, NULL, NULL, NULL, {0, 101000}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {2, 0}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {2, 0}) = 0 (Timeout)
select(0, NULL, NULL, NULL, {2, 0}^C <unfinished ...>
Those are the 2 noisy threads.
-Steve
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