From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Parallel Aggregates for string_agg and array_agg |
Date: | 2018-05-01 20:59:35 |
Message-ID: | 15683.1525208375@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Mar 26, 2018 at 4:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I fear that what will happen, if we commit this, is that something like
>> 0.01% of the users of array_agg and string_agg will be pleased, another
>> maybe 20% will be unaffected because they wrote ORDER BY which prevents
>> parallel aggregation, and the remaining 80% will scream because we broke
>> their queries. Telling them they should've written ORDER BY isn't going
>> to cut it, IMO, when the benefit of that breakage will accrue only to some
>> very tiny fraction of use-cases.
> I think your estimated percentages here are wildly inaccurate.
My estimate for the number of people positively impacted could be off
by a factor of a thousand, and it still wouldn't change the conclusion
that this will hurt more people than it helps.
I see that I'm in the minority on this, so I'm prepared to accept defeat,
but I stand by that conclusion.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Stas Kelvich | 2018-05-01 21:02:47 | Re: Global snapshots |
Previous Message | Andres Freund | 2018-05-01 20:57:08 | Re: Explain buffers wrong counter with parallel plans |