[pgpool-hackers: 1822] Re: [pgpool-committers: 3514] pgpool: Fixing a problem with the watchdog failover_command locking mec

[Tatsuo Ishii]

Usama,

Why wasn't this be back patched to the 3.5 stable tree?
It seems Pgpool-II 3.5 watchdog has sevior problem.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp

From: Muhammad Usama <m.usama at gmail.com>
Subject: [pgpool-committers: 3514] pgpool: Fixing a problem with the watchdog failover_command locking mec
Date: Mon, 19 Sep 2016 19:45:53 +0000
Message-ID: <E1bm4Vl-0004ap-B9 at gothos.postgresql.org>

> Fixing a problem with the watchdog failover_command locking mechanism
> 
>>From pgpool-II 3.5 watchdog was using the separate individual locks for each
> node-failover command(failover, failback and follow-master) and the lock was
> acquired just before executing the respective failover script and was released
> as soon as the script execution finishes. This technique although was very
> efficient but also had a problem. If the failover command takes a very little
> time and gets finished before the lock request from other pgpool-II node
> arrives, the other node is also granted a lock, since the lock was already
> released by the first node at that time. Consequently, both nodes ends up
> executing the failover script.
> So to fix this we are reverting back to the tested failover interlocking design
> used prior to pgpool-II 3.5 where all the commands gets locked at the failover
> start by the node that becomes a lock-holder and each command lock is released
> after its execution finishes. And only the lock-holder node is allowed to
> acquire/release the individual command lock. That way the lock-holder node
> keeps the lock-holder status throughout the span of the failover execution and
> the system becomes less time sensitive.
> 
> The issue was identified by Yugo<nagata at sraoss.co.jp>
> 
> Branch
> ------
> master
> 
> Details
> -------
> http://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=233ae462a417fb2d5919a2eac900b17348a7ca8b
> 
> Modified Files
> --------------
> src/include/pool.h                     |   4 +-
> src/include/watchdog/wd_ipc_commands.h |  14 +-
> src/include/watchdog/wd_ipc_defines.h  |  32 ++-
> src/main/pgpool_main.c                 |  64 +++---
> src/watchdog/watchdog.c                | 395 +++++++++++++++++++++------------
> src/watchdog/wd_commands.c             |  79 +++----
> 6 files changed, 351 insertions(+), 237 deletions(-)
> 
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