Re: many updates to single row in single transaction

On 8 Jul 2005, Adam Pritchard wrote:
> so I have a singleton table that keeps track of where we are in the
> pseudo-sequence.  The table is very simple:
>
>  CREATE TABLE t ( next BIGINT );
>  INSERT INTO t ( next ) VALUES ( 0 );
>
> UPDATE t SET next = $1; -- $1 = next+1
>
> The problem is that the performance of those operations is pretty slow
>
> 1000: 891ms
> 2000: 1296ms
> 3000: 1735ms
> 4000: 2312ms
> 5000: 2844ms
> 6000: 3328ms
> 7000: 3875ms
> 8000: 4531ms
> 9000: 4875ms

Looks like you need to vacuum that table very, very often. Each time you
update the counter you get a dead row that needs to be vacuumed. You can't
vacuum inside a transaction, but maybe that is not a problem in your case.

For bulk loading in a transaction you might also be able to lock the table
to prevent others from using it and then insert 1000 rows and do:

 UPDATE t SET next = next + 1000;

--
/Dennis Björklund