Re: Logical decoding on standby

From: Craig Ringer <craig(at)2ndquadrant(dot)com>
To: Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Thom Brown <thom(at)linux(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Logical decoding on standby
Date: 2017-03-23 08:07:37
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On 23 March 2017 at 00:13, Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com> wrote:
> On 22 March 2017 at 08:53, Craig Ringer <craig(at)2ndquadrant(dot)com> wrote:
>> I'm splitting up the rest of the decoding on standby patch set with
>> the goal of getting minimal functionality for creating and managing
>> slots on standbys in, so we can maintain slots on standbys and use
>> them when the standby is promoted to master.
>> The first, to send catalog_xmin separately to the global xmin on
>> hot_standby_feedback and store it in the upstream physical slot's
>> catalog_xmin, is attached.
>> These are extracted directly from the logical decoding on standby
>> patch, with comments by Petr and Andres made re the relevant code
>> addressed.
> I've reduced your two patches back to one with a smaller blast radius.
> I'll commit this tomorrow morning, barring objections.

This needs rebasing on top of

commit af4b1a0869bd3bb52e5f662e4491554b7f611489
Author: Simon Riggs <simon(at)2ndQuadrant(dot)com>
Date: Wed Mar 22 16:51:01 2017 +0000

Refactor GetOldestXmin() to use flags

Replace ignoreVacuum parameter with more flexible flags.

Author: Eiji Seki
Review: Haribabu Kommi

That patch landed up using PROCARRAY flags directly as flags to
GetOldestXmin, so it doesn't make much sense to add a flag like
PROCARRAY_REPLICATION_SLOTS . There won't be any corresponding PROC_
flag for PGXACT->vacuumFlags, replication slot xmin and catalog_xmin
are global state not tracked in individual proc entries.

Rather than add some kind of "PROC_RESERVED" flag in proc.h that would
never be used and only exist to reserve a bit for use for
PROCARRAY_REPLICATION_SLOTS, which we'd use a flag to GetOldestXmin, I
added a new argument to GetOldestXmin like the prior patch did.

If preferred I can instead add


#define PROC_RESERVED 0x20



and then test for (flags & PROCARRAY_REPLICATION_SLOTS)

but that's kind of ugly to say the least, I'd rather just add another argument.

Craig Ringer
PostgreSQL Development, 24x7 Support, Training & Services

Attachment Content-Type Size
0001-Report-catalog_xmin-separately-to-xmin-in-hot-standb.patch text/x-patch 21.9 KB

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