Re: record-based log shipping

On Sun, Aug 21, 2011 at 08:23, Dondi Michael Stroma <dstroma@gmail.com> wrote:
> Hello,
>
> I have a question about log shipping. The documentation from
> PostgreSQL 8.4, in section 24.4.4, describes how to archive partial
> WAL files by using the pg_xlogfile_name_offset() function, which it
> calls "record-based log shipping". Although it seems that this section
> of documentation has been removed in 9.0, the capability is apparently
> still there. (Of course 9.0 comes with streaming replication, but the
> ability to perform archiving this way is attractive as it can be used
> to replicate the database to a non-sql data storage system.)
>
> Well, I have successfully written an archiving script to copy the
> partial WAL segments as described, but I am confused as to how I would
> actually use this data for a recovery.
>
> Section 24.4.4 states that the "restore_command scripts still deal in
> whole WAL files, so the incrementally copied data is not ordinarily
> made available to the standby servers. It is of use only when the
> primary dies — then the last partial WAL file is fed to the standby
> before allowing it to come up."
>
> So how would one "feed" incrementally copied partial WAL file data to
> a standby (actually a new server used for recovery) as suggested
> above?

Pad it with zeroes up to the normal segment limit (16Mb), and feed
that. PostgreSQL will detect when the correct data ends and the
padding begins.

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 Magnus Hagander
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