Re: Pluggable Storage - Andres's take

From: Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
To: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, 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: 2018-10-29 04:55:49
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On Mon, Oct 29, 2018 at 7:40 AM Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote:

> > On Fri, 26 Oct 2018 at 13:25, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>
> wrote:
> >
> > Here I attached the cumulative patch with all fixes that are shared in
> earlier mails by me.
> > Except fast_default test, rest of test failures are fixed.
> Hi,
> If I understand correctly, these patches are for the branch
> "pluggable-storage"
> in [1] (at least I couldn't apply them cleanly to "pluggable-zheap"
> branch),
> right?

Yes, the patches attached are for pluggable-storage branch.

> I've tried to experiment a bit with the current status of the patch, and
> accidentally stumbled upon what seems to be an issue - when I run pgbench
> agains it with some significant number of clients and script [2]:
> $ pgbench -T 60 -c 128 -j 64 -f zipfian.sql

Thanks for testing the patches.

> I've got for some client an error:
> client 117 aborted in command 5 (SQL) of script 0; ERROR:
> unrecognized heap_update status: 1

This error is for the tuple state of HeapTupleInvisible, As per the comments
in heap_lock_tuple, this is possible in ON CONFLICT UPDATE, but because
of reorganizing of the table_lock_tuple out of EvalPlanQual(), the invisible
error is returned in other cases also. This case is missed in the new code.

> This problem couldn't be reproduced on the master branch, so I've tried to
> investigate it. It comes from nodeModifyTable.c:1267, when we've got
> HeapTupleInvisible as a result, and this value in turn comes from
> table_lock_tuple. Everything points to the new way of handling
> HeapTupleUpdated
> result from heap_update, when table_lock_tuple call was introduced. Since I
> don't see anything similar in the master branch, can anyone clarify why is
> this
> lock necessary here?

In the master branch code also, there is a tuple lock that is happening in
EvalPlanQual() function, but pluggable-storage code, the lock is kept
and also function call rearrangements, to make it easier for the table
methods to provide their own MVCC implementation.

> Out of curiosity I've rearranged the code, that handles
> HeapTupleUpdated, back to switch and removed table_lock_tuple (see the
> attached
> patch, it can be applied on top of the lastest two patches posted by
> Haribabu)
> and it seems to solve the issue.

Thanks for the patch. I didn't reproduce the problem, based on the error
your mail, the attached draft patch of handling of invisible tuples in
update and
delete cases should also fix it.

Haribabu Kommi
Fujitsu Australia

Attachment Content-Type Size
0001-Handling-HeapTupleInvisible-case.patch application/octet-stream 1.2 KB

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