[mythtv-users] Slow MySQL query after delete
Dan Wilga
mythtv-users2 at dwilga-linux1.amherst.edu
Tue Sep 4 14:16:07 UTC 2007
Running the original query I got:
1798 rows in set (2.91 sec)
I also ran the EXPLAIN on my DB and did not come up with any
significant differences.
Normally, when looking at EXPLAINs, the kiss of death is "Using
temporary; Using filesort". This indicates that MySQL has to create a
temporary, sometimes disk-based, table to hold the intermediate
results. If it does have to go to disk, this can be very slow.
But the good news here is that you're only dealing with 2 rows in
that part of the query, so even if it did have to use a temp table on
disk, it should be really quick. I suggest you look at your DB
optimization settings. In /etc/my.conf I've been using these for some
time:
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
skip-innodb
max_allowed_packet = 1M
table_cache = 256
sort_buffer_size = 4M # was 512K
net_buffer_length = 8K
read_buffer_size = 1M # was 512K
read_rnd_buffer_size = 1M
key_buffer = 16M
query_cache_size = 16M
--
Dan Wilga "Ook."
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