Re: [HACKERS] GSoC 2017: weekly progress reports (week 6)

From: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
To: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Shubham Barai <shubhambaraiss(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Andrew Borodin <amborodin86(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)gmail(dot)com>
Subject: Re: [HACKERS] GSoC 2017: weekly progress reports (week 6)
Date: 2018-04-09 06:23:21
Message-ID: fe55ac37-576d-d806-d1b7-c745b0a4892a@iki.fi
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On 16/03/18 00:26, Alexander Korotkov wrote:
> On Tue, Mar 13, 2018 at 3:26 PM, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>> On 13/03/18 14:02, Alexander Korotkov wrote:
>>> And what happen if somebody concurrently set (fastupdate = on)?
>>> Can we miss conflicts because of that?
>>
>> No, AccessExclusiveLock will prevent this kind of problems with enabling
>> fastupdate.
>
> True. I didn't notice that ALTER INDEX SET locks index in so high mode.
> Thus, everything is fine from this perspective.

Nope, an AccessExclusiveLock is not good enough. Predicate locks stay
around after the transaction has committed and regular locks have been
released.

Attached is a test case that demonstrates a case where we miss a
serialization failure, when fastupdate is turned on concurrently. It
works on v10, but fails to throw a serialization error on v11.

- Heikki

Attachment Content-Type Size
predicate-gin-fastupdate-fail-demo.patch text/x-patch 2.7 KB

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