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From: Stephen Frost <sfrost@snowman.net>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: David Steele <david@pgmasters.net>
Cc: Andres Freund <andres@anarazel.de>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: WIP: WAL prefetch (another approach)
Date: Fri, 5 Jun 2020 20:36:32 -0400
Message-ID: <20200606003632.GS6680@tamriel.snowman.net> (raw)
In-Reply-To: <20200605223422.r76a5rpl2zg2xo34@development>
References: <CA+hUKGKGhsRHhHJ4ybftCOjRxErnJYj-yOVamQaAsNmUBx4Aqg@mail.gmail.com>
	<CA+hUKGK6F66K9MJkLPBXTAxH8TM2Ozs7-FTbqsmJaHYVUOLDVg@mail.gmail.com>
	<226b5950-7404-a51d-8dc7-53895b363a38@pgmasters.net>
	<CA+hUKG+AzDLtAo1R3kxLW0nKRYd9euiBhW92OW1OCjkRU2E1pQ@mail.gmail.com>
	<20200419114820.h62ryte7uwu46e2x@localhost>
	<CA+hUKGJ7_niJzcCHX5JWFo-05pLbzwukQfFgQi4-h46yZh=tqA@mail.gmail.com>
	<20200425191935.4p6qxzzu5bklodwk@localhost>
	<20200502151423.yf52i63u232fdfrg@localhost>
	<CA+hUKG+obB-e_VFa2uPVe52DvtpBQtC30vyo_PDURJQTr3SdJQ@mail.gmail.com>
	<20200605223422.r76a5rpl2zg2xo34@development>

Greetings,

* Tomas Vondra (tomas.vondra@2ndquadrant.com) wrote:
> I wonder if we can collect some stats to measure how effective the
> prefetching actually is. Ultimately we want something like cache hit
> ratio, but we're only preloading into page cache, so we can't easily
> measure that. Perhaps we could measure I/O timings in redo, though?

That would certainly be interesting, particularly as this optimization
seems likely to be useful on some platforms (eg, zfs, where the
filesystem block size is larger than ours..) and less on others
(traditional systems which have a smaller block size).

Thanks,

Stephen

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