Обсуждение: update performance 8.1.4

Hi,

How can I speed up updates?
i try an
  update tablename set datecol=null
~ 2.3 mio rows

After 6 hours, this was still not finished. selects and inserts are ok.
System is a dual xeon, 8gb ram, debian 64bit, pg 8.1.4

thanks
thomas






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2008/1/15 Thomas Markus <t.markus@proventis.net>:
> Hi,
>
> How can I speed up updates?
> i try an
>   update tablename set datecol=null
> ~ 2.3 mio rows

Got any foreign keys against that table?  If so, they need to be
indexed on the other end.

What's the schema of that table and any related tables?

>>> On Tue, Jan 15, 2008 at  3:33 AM, in message <478C7DEC.1020806@proventis.net>,
Thomas Markus <t.markus@proventis.net> wrote:

>   update tablename set datecol=null
> ~ 2.3 mio rows
>
> After 6 hours, this was still not finished. selects and inserts are ok.
> System is a dual xeon, 8gb ram, debian 64bit, pg 8.1.4

You do realize that every row updated is a delete and an insert,
right?  So this should take as long as a single database transaction
which deleted all the rows in the table and inserted them again.

If datecol is null in any rows, you should try:

update tablename set datecol=null where datecol is not null;

If you have canceled the update because of the long run time, you
will have left a lot of dead rows in the table, which will make the
next attempt run even longer.  Be sure you are doing vacuums.

-Kevin