| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Brian Tarbox" <btarbox(at)theworld(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: why Sequencial Scan when selecting on primary key of table? |
| Date: | 2003-05-31 17:55:01 |
| Message-ID: | 21289.1054403701@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
"Brian Tarbox" <btarbox(at)theworld(dot)com> writes:
> The primary key field is an integer and I have performed vacuum analyse but
> that does not seem to change anything.
Hm. So how big is the table, exactly? On small tables a seqscan will
be preferred because the extra I/O to examine the index costs more than
the CPU to examine all the tuples on a disk page.
> I've also heard that postgres will not indexes when JOINing tables. Can
> that really be true??
We have some join methods that like indexes and we have some that find
no benefit in 'em. Again, testing on toy-size tables is not a good
guide to what will happen on larger tables.
regards, tom lane
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