Re: [PERFORM] Difference between 8.1 & 8.3

Patrick Vachon wrote:

> Hi guys,
>
> I've got a query that is running slower on 8.3 than on 8.1 (with
> equivalent server config),
> because the join ordering is not the same, at least that's my guess... ;-)
>
> In 8.1.4, table A had 122880 pages, B 112690 pages and C 80600 pages.
> Now in 8.3.3, table A has only 77560 pages, B 69580 but C remains at
> 80600 pages.
>
> In 8.1 the tables were joined in that way (using explain analyse):
> C join A join B
> now in 8.3:
> B join A join C
> Beside that, the plan is very similar, but the indexes used are not the
> same.
>
> Could the number of disk pages of a table influence the
> order in which it is joined, even when it is scanned with an index?
>
> I'm pretty sure it is because of the reduced table sizes,
> since the server configuration is the same.
>
> Thoughts?

8.3 has fewer automatic casts to text types; perhaps you have indexes which are not being used because of mismatched types ? Perhaps an EXPLAIN ANALYZE from both, if possible, would clairfy.

HTH,

Greg Williamson
Senior DBA
DigitalGlobe

Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information and must be protected in accordance with those provisions. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message.

(My corporate masters made me say this.)