On Fri, Apr 23, 2010 at 12:09 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Fri, Apr 23, 2010 at 7:12 AM, Heikki Linnakangas
>> <heikki.linnakangas@enterprisedb.com> wrote:
>>> Streaming replication needs the same information in the WAL as archiving
>>> does,
>
>> True.
>
> FWIW, I still don't believe that claim, and I think it's complete folly
> to set the assumption in stone by choosing a user-visible GUC API that
> depends on it being true.
Huh? We're clearly talking about two different things here, because
that doesn't make any sense. Archiving and streaming replication are
just two means of transporting WAL records from point A to point B.
By definition, any two manners of moving a byte stream around are
isomorphic and can't possibly affect what that byte stream does or
does not need to contain. What affects the WAL that must be emitted
is the purpose for which it is to be used. As to that, I believe
everyone (including the code) is in agreement that a minimum amount of
WAL is always needed for crash recovery, plus if we want to do archive
recovery on another server there are some additional bits that must be
emitted (XLogIsNeeded) and plus if further want to process queries on
the standby then there are a few more bits beyond that
(XLogStandbyInfoActive).
...Robert