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From: Heikki Linnakangas <hlinnaka@iki.fi>
To: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: PATCH: adaptive ndistinct estimator v4
Date: Thu, 30 Apr 2015 14:31:48 -0700
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On 04/30/2015 01:57 PM, Robert Haas wrote:
>
> 2. There should be a compatibility GUC to restore the old behavior.
> The new behavior should be the default, because if we're not confident
> that the new behavior will be better for most people, we have no
> business installing it in the first place (plus few people will try
> it).  But just in case it turns out to suck for some people, we should
> provide an escape hatch, at least for a few releases.

You can override the ndistinct estimate with ALTER TABLE. I think that's 
enough for an escape hatch.

- Heikki



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