[rt-users] Severe performance problems suddenly in RT 3.8.2

[Tim Cutts]

On 17 Feb 2009, at 10:52 pm, Jesse Vincent wrote:

>> OK, OPTIMIZE TABLE done, but performance on SELECT COUNT(id) FROM
>> Attachments is still terrible:
>>
>> This does sort of smell like an optimiser bug - it says it's using
>> indices, but the level of I/O being done by the machine suggests it's
>> actually performing a full table scan.
>
> Indeed. Before you dig deeply into what's going on with this version  
> of
> mysql, coming up to a current 5.0.x probably makes sense.

OK, I've just moved up to 5.0.51a, as supplied in etch-backports, and  
the problem persists.  An ANALYZE TABLE on the Attachments table has  
helped a bit with the ludicrous statistics from EXPLAIN, but they're  
now just very silly rather than ludicrous:

mysql> explain select count(id) from Attachments;
+----+-------------+-------------+-------+---------------+--------- 
+---------+------+---------+-------------+
| id | select_type | table       | type  | possible_keys | key     |  
key_len | ref  | rows    | Extra       |
+----+-------------+-------------+-------+---------------+--------- 
+---------+------+---------+-------------+
|  1 | SIMPLE      | Attachments | index | NULL          | PRIMARY |  
4       | NULL | 2324446 | Using index |
+----+-------------+-------------+-------+---------------+--------- 
+---------+------+---------+-------------+

A reload might be the way forward here.

There is a part of me wondering what suddenly broke this today.  I'm  
currently searching the table for suspiciously large looking  
attachments.

Tim


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