Question

I have the following query running against a MySQL db every 30 seconds:

SELECT message.id FROM message WHERE userto='13689' AND tstampviewed IS NULL AND message.status != 'VOID';

It shows up in my slow query log a lot, but it looks to me like it is optimized as best as can be.

The result of EXPLAIN:

SELECT_TYPE = Simple

TABLE = message

TYPE = ref

POSSIBLE_KEYS = userto,tst,stat

KEY = userto

KEY_LEN = 53

REF = const

ROWS = 1

EXTRA = “Using Where”

The keys userto, tst, and stat are all normal BTREE indexes, one for each of the varchar fields referenced in the whereclause of the query. It is a MyISAM table with 300K rows. Users do write to the table consistently, but reads are much more likely (10/1 ratio of reads to writes). The db server is Windows 2008 Enterprise with a lot of CPU and fast drives.

Over the past month, we keep getting max_connection errors, even though I increased the max_connections from 750 to 1500. Several times a day, it seems like a query hangs (I can’t verify this because I don’t have access to the process list in real time), and 1500 queries pile up behind it and max out the connections. This then obviously causes a lot of other problems.

The above query is the one that consistenly comes up in the slow query log, even though I thought it was optimized as best as possible. Can anyone tell me otherwise or point me in the right direction to solve this problem?

Thanks in advance.

Answer 1

The problem is not on the query – you are opening a connection to the database and not closing it, but opening a new one each time.