Horton

Re: Attempt to consolidate reading of XLOG page

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Antonin Houska <ah@cybertec.at>, Thomas Munro <thomas.munro@gmail.com>, Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-11-22T13:40:07Z
Lists: pgsql-hackers 
On Fri, Nov 22, 2019 at 10:35:51AM -0300, Alvaro Herrera wrote:
> FWIW I think the new code is buggy because it doesn't seem to be setting
> ws_off, so I suppose the optimization in ReadPageInternal to skip
> reading the page when it's already the page we have is not hit, except
> for the first page in the segment.  I didn't verify this, just my
> impression while reading the code.

FWIW, this matches with my impression here, third paragraph:
https://www.postgresql.org/message-id/20191120083802.GB47145@paquier.xyz
--
Michael

Commits

  1. Remove logical_read_local_xlog_page

  2. Refactor WAL file-reading code into WALRead()

  3. Rework WAL-reading supporting structs

  4. Make XLogReaderInvalReadState static

  5. Use pg_pread() and pg_pwrite() for data files and WAL.