On 12/12/11 7:46 PM, Paul J Stevens wrote:
On 12/12/2011 03:15 AM, Yaroslav Tykhiy wrote:
CREATE INDEX dbmail_messages_mbox_msg ON dbmail_messages
(mailbox_idnr,message_idnr);
Sounds great. Surprising given the existing indexes, but great.
I wouldn't say it's too surprising. With the stock indexes, the DB can
efficiently locate all messages in a given mailbox, but then it has to
scan those records sequentially to find out MAX(message_idnr), which can
be slow in a large mailbox. And with this custom index it can just
fetch the MAX value from the index because it's btree by default in Pg.
Wonder if this would also benefit mysql users...
IMHO it's likely to provided that the mysql indexes used are ordered.
E.g., a btree will do but a hash won't -- sorry, I have no idea what
actual mysql index types are so I'm just speculating here.
Yar
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