Обсуждение: Optimizer and Indexes with Joins

"Hargis" <ljhargis@vcn.com> writes:
> I am trying to=
> find out if postgresql has a way to basically tell the optimizer which ind=
> ex to use.

No.

> If I need to provide any further information, please advise....

Specific problem examples would be interesting: queries, table schemas,
EXPLAIN output.

            regards, tom lane

Sorry, you can't tell pg what index to use.

You can usually get pg to use your indexes by changes to query and/or
schema.  If you post a new message to list, that says "why isn't this query
using index7?", and then include:

1) A copy of your query
2) The output of "explain <query>"
3) schema (you can use "pg_dump -s -t <table> <database>" for each table in
query).

The explanations/suggestions provided by others will quickly teach you a
lot about how pg works in your environment.

Frank

At 10:01 PM 04/03/02 -0700, Hargis wrote:
>I have a question regarding the optimizer and indexes.   Having a boss
>that is fluent in data flex but trying to understand postgresql, I am
>trying to find out if postgresql has a way to basically tell the optimizer
>which index to use.  The boss states that in data flex you "tell" it to
>use index 7 and it uses index 7.
>
>We utilize vacuum analyze and we also structure our where clauses to fit
>the specific indexes.  Further, we set the "enable sequence scan" to off
>and it did not improve any performace issues.  Most of our selects are
>"joins" though and that may be causing most of our performance
>issues.  Any advice out there?
>
>If I need to provide any further information, please advise....
>
>TIA,
>
>LA Hargis
>(Trying to get better at postgres)
>