Tom Lane wrote:
Chris <dmagick@xxxxxxxxx> writes:
I'm trying to do an update of a reasonably large table and it's taking
way too long so I'm trying to work out why and if I need to tweak any
settings to speed it up.
Any foreign keys leading to or from that table?
Nope :(
3.5 million row updates are not exactly gonna be instantaneous anyway,
but only FK checks or really slow user-written triggers would make it
take upwards of an hour ...
No triggers, functions.
Table is pretty basic.
I have a few indexes (one on the primary key, one on emailaddress etc)
but the 'domainname' column is a new one not referenced by any of the
indexes.
FWIW (while the other update is still going in another window):
select SUBSTRING(emailaddress FROM POSITION('@' IN emailaddress)) from
table;
Time: 28140.399 ms
Is there a better way to write the update? I thought about something
like this (but couldn't get it working - guess I don't have the right
syntax):
update t1 set domainname=(select id, SUBSTRING(emailaddress FROM
POSITION('@' IN emailaddress)) from table t2) AS t2 where t1.id=t2.id
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