Re: Pluggable Storage - Andres's take

From: Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Pluggable Storage - Andres's take
Date: 2018-10-22 07:16:47
Message-ID: CAJrrPGeMbTKPa8qAKWJnQGKYzNOb_O9jS=Ee3v1=xu8mxi7-Fw@mail.gmail.com
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On Thu, Oct 18, 2018 at 1:04 PM Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
wrote:

> On Tue, Oct 9, 2018 at 1:46 PM Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
> wrote:
>
>>
>> I also observed the failure of aggregates.sql, will look into it.
>>
>
> The random failure of aggregates.sql is as follows
>
> SELECT avg(a) AS avg_32 FROM aggtest WHERE a < 100;
> ! avg_32
> ! ---------------------
> ! 32.6666666666666667
> (1 row)
>
> -- In 7.1, avg(float4) is computed using float8 arithmetic.
> --- 8,16 ----
> (1 row)
>
> SELECT avg(a) AS avg_32 FROM aggtest WHERE a < 100;
> ! avg_32
> ! --------
> !
> (1 row)
>
> Same NULL result for another aggregate query on column b.
>
> The aggtest table is accessed by two tests that are running in parallel.
> i.e aggregates.sql and transactions.sql, In transactions.sql, inside a
> transaction
> all the records in the aggtest table are deleted and aborted the
> transaction,
> I suspect that some visibility checks are having some race conditions that
> leads
> to no records on the table aggtest, thus it returns NULL result.
>
> If I try the scenario manually by opening a transaction and deleting the
> records, the
> issue is not occurring.
>
> I am yet to find the cause for this problem.
>

I am not yet able to generate a test case where the above issue can occur
easily for
debugging, it is happening randomly. I will try to add some logs to find
out the problem.

During the checking for the above problem, I found some corrections,
1. Remove of the tableam_common.c file as it is not used.
2. Remove the extra heaptuple visibile check in heapgettup_pagemode function
3. New API for init fork.

Regards,
Haribabu Kommi
Fujitsu Australia

Attachment Content-Type Size
0003-init-fork-API.patch application/octet-stream 6.8 KB
0002-Remove-the-extra-Tuple-visibility-function.patch application/octet-stream 1.7 KB
0001-Remove-the-old-slot-interface-file-and-also-update-t.patch application/octet-stream 1.1 KB

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