From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: Simon Riggs <simon@2ndquadrant.com>,
        Andrew Dunstan <andrew.dunstan@2ndquadrant.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>,
        Dean Rasheed <dean.a.rasheed@gmail.com>
Subject: Re: WITH clause in CREATE STATISTICS
In-reply-to: <20170512204800.iqt2uwyx3c32j45r@alvherre.pgsql>
References: <20170512204800.iqt2uwyx3c32j45r@alvherre.pgsql>
Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
	message dated "Fri, 12 May 2017 17:48:01 -0300"
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Date: Fri, 12 May 2017 17:20:04 -0400
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Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Tom Lane wrote:
>> Although I've not done anything about it here, I'm not happy about the
>> handling of dependencies for stats objects.

> Here are two patches regarding handling of dependencies.

Oh, sorry --- I already pushed something about this.

> The first one
> implements your first suggestion: add a NORMAL dependency on each
> column, and do away with RemoveStatisticsExt.  This works well and
> should uncontroversial.

No, I wanted an AUTO dependency there, for exactly the reason you
mention:

> If we only do this, then DROP TABLE needs to say CASCADE if there's a
> statistics object in the table.

I don't think we really want that, do we?  A stats object can't be of
any value if the underlying table is gone.  Perhaps that calculus
would change for cross-table stats but I don't see why.

> This seems pointless to me, so the
> second patch throws in an additional dependency on the table as a whole,
> AUTO this time, so that if the table is dropped, the statistics goes
> away without requiring cascade.  There is no point in forcing CASCADE
> for this case, ISTM.  This works well too, but I admit there might be
> resistance to doing it.  OTOH this is how CREATE INDEX works.

Uh, no it isn't.  Indexes have auto dependencies on the individual
columns they index, and *not* on the table as a whole.

			regards, tom lane


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