Horton

Re: Attempt to consolidate reading of XLOG page

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Michael Paquier <michael@paquier.xyz>, Thomas Munro <thomas.munro@gmail.com>, Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2019-11-22T22:56:32Z
Lists: pgsql-hackers

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On 2019-Nov-22, Antonin Houska wrote:

> As I pointed out in
> 
> https://www.postgresql.org/message-id/88183.1574261429%40antos
> 
> seg.ws_off only replaced readOff in XLogReaderState. So we should only update
> ws_off where readOff was updated before commit 709d003. This does happen in
> ReadPageInternal (see HEAD) and I see no reason for the final patch to update
> ws_off anywhere else.

Oh you're right.

I see no reason to leave ws_off.  We can move that to XLogReaderState; I
did that here.  We also need the offset in WALReadError, though, so I
added it there too.  Conceptually it seems clearer to me this way.

What do you think of the attached?

BTW I'm not clear what errors can pread()/pg_pread() report that do not
set errno.  I think lines 1083/1084 of WALRead are spurious now.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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.