Horton

Re: Attempt to consolidate reading of XLOG page

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org
Date: 2019-04-15T09:27:36Z
Lists: pgsql-hackers 
Alvaro Herrera <alvherre@2ndquadrant.com> wrote:

> I agree that xlog reading is pretty messy.
> 
> I think ifdef'ing the way XLogRead reports errors is not great.  Maybe
> we can pass a function pointer that is to be called in case of errors?

I'll try a bit harder to evaluate the existing approaches to report the same
error on both backend and frontend side.

> Not sure about the walsize; maybe it can be a member in XLogReadPos, and
> given to XLogReadInitPos()?  (Maybe rename XLogReadPos as
> XLogReadContext or something like that, indicating it's not just the
> read position.)

As pointed out by others, XLogReadPos is not necessary. So if XLogRead()
receives XLogReaderState instead, it can get the segment size from there.

Thanks.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com

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.