checkpoints are duplicated even while the system is idle

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: checkpoints are duplicated even while the system is idle
Date: 2011-10-05 05:19:44
Message-ID: CAHGQGwFEjkNRMTjyvVtYWhuTJkDYTQBb95Oebm4yMXd_9CBx7A@mail.gmail.com
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Hi,

While the system is idle, we skip duplicate checkpoints for some
reasons. But when wal_level is set to hot_standby, I found that
checkpoints are wrongly duplicated even while the system is idle.
The cause is that XLOG_RUNNING_XACTS WAL record always
follows CHECKPOINT one when wal_level is set to hot_standby.
So the subsequent checkpoint wrongly thinks that there is inserted
record (i.e., XLOG_RUNNING_XACTS record) since the start of the
last checkpoint, the system is not idle, and this checkpoint cannot
be skipped. Is this intentional behavior? Or a bug?

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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