| From: | Francisco Reyes <lists(at)natserv(dot)com> |
|---|---|
| To: | PostgreSQL performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Understanding explains |
| Date: | 2004-10-11 21:04:16 |
| Message-ID: | 20041011164950.J97379@zoraida.natserv.net |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
Is there a tutorial or reference to the different terms that appear on the
explain output?
Items such as "Nested Loop", "Hash"..
Also is there a way to easily tell which of two explains is "worse".
Example I am running a query with "set enable_seqscan to off;" and i see
the explain now shows index scans, but not sure if is any faster now.
I tried "explain analyze" and the "total runtime" for the one with
seq_scan off was faster, but after repeathing them they both dropped in
time, likely due to data getting cached. Even after the time drops for
both the one with seqscan off was always faster.
Is there any disadvantage of having the enable_seqscan off?
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| Next Message | Gabriele Bartolini | 2004-10-11 21:05:59 | Normal case or bad query plan? |
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