Re: Boom filters for hash joins (was: A design for amcheck heapam verification)

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Boom filters for hash joins (was: A design for amcheck heapam verification)
Date: 2017-09-18 21:07:58
Message-ID: CA+TgmoYKT64JYN6E9Kfb3PRKwuP0ORY1CJDU3ibBuYBsHjcCqA@mail.gmail.com
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On Mon, Sep 18, 2017 at 1:29 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Uh, why does the planner need to be involved at all?

Because it loses if the Bloom filter fails to filter anything. That's
not at all far-fetched; consider SELECT * FROM a.x, b.x WHERE a.x =
b.x given a foreign key on a.x referencing b(x).

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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