Re: are WAL file segment boundaries a point of consistency?

I would look at WAL files as a sequence of commits and not a sequence of
files within timelines where you can specify either with recovery_target_time
or recovery_target_xid the point of consistency you want to reach.

Cheers,
A.A.

On Fri, Sep 6, 2013 at 1:26 PM, John Lumby <johnlumby(at)hotmail(dot)com> wrote:

> We use logshipping replication, and have recently noticed a nasty bug
> where, in certain very rare cases, the primary archive_command program
> will fail to send the WAL file to the standby but report good return code
> 0 to postgresql.
> In such cases, if the standby then triggers its termination of recovery
> mode,
> it will come up in normal accessible mode but missing the log records from
> that last WAL file.
>
> This is a bug in our code which we will fix, but I am wondering if it
> means there is a possibility
> of worse than missing some updates. I.e. could it result in this
> was-standby cluster now having
> a corrupt database (e.g. an index entry with no matching heap slot or
> something like that - or worse)?
>
> I think the question is whether the end of a WAL file is a point of
> consistency?
> like the timestamp you can specify in the recovery.conf for a
> point-in-time recovery?
> Or does postgresql xlogger just chop each WAL segment at the physical page
> boundary?
>
> Cheers, John Lumby
>
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