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Re: Checkpointer vs pg_stat_bgwriter

From: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>
Subject: Re: Checkpointer vs pg_stat_bgwriter
Date: 2012-02-28 06:06:29
Message-ID: CAHGQGwE+66oOE_4XbkR0PwsVH1uCWRuVbuzL7dvWLQNsgS1tew@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Feb 27, 2012 at 4:24 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
> Hi!
>
> I admit to not having actually tested this since I don't have a good
> cluster to test it on right now, but from what I can tell the code in
> the new checkpointer process only sends statistics to the collector
> once the checkpoint is finished (checkpointer.c, line 549). The 9.1
> and earlier sent this every time they entered a delay state (in
> BgWriterNap() called from CheckpointWriteDelay()).
>
> So in 9.1 and earlier we could see how a checkpoint wrote things as it
> was running, but in 9.2 we'll get it all as one big block at the end
> of the checkpoint - which can be a lot later in the spread case.
>
> Am I reading the code right?
>
> And if so, was this an intentional change, and if so why? To me it
> seems like a loss of functionality that should be fixed..

I agree that this should be fixed.

Regards,

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

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