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Re: Group by more efficient than distinct?
- From: Francisco Reyes <lists(at)stringsutils(dot)com>
- To: PFC <lists(at)peufeu(dot)com>
- Cc: Gregory Stark <stark(at)enterprisedb(dot)com>, Pgsql performance <pgsql-performance(at)postgresql(dot)org>
- Subject: Re: Group by more efficient than distinct?
- Date: Sun, 20 Apr 2008 11:15:36 -0400
- Message-id: <cone(dot)1208704536(dot)428347(dot)85914(dot)1000(at)zoraida(dot)natserv(dot)net>
PFC writes:
- If you process up to some percentage of your RAM worth of data, hashing is going to be a lot faster
Thanks for the excellent breakdown and explanation. I will try and get sizes of the tables in question and how much memory the machines have.
- If you need DISTINCT ON, well, you're stuck with the Sort - So, for the time being, you can replace DISTINCT with GROUP BY...
Have seen a few of those already on some code (new job..) so for those it is a matter of having a good disk subsystem?
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