Re: Re: Synch Rep: direct transfer of WAL file from the primary to the standby

Fujii Masao wrote:
> On Wed, Jul 8, 2009 at 4:00 AM, Heikki
> Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>>> I would envision the slaves
>>> connecting to the master's replication port and asking "feed me WAL
>>> beginning at LSN position thus-and-so", with no notion of WAL file
>>> boundaries exposed anyplace.
>> Yep, that's the way I envisioned it to work in my protocol suggestion
>> that Fujii adopted
>> (http://archives.postgresql.org/message-id/4951108A.5040608@enterprisedb.com)
>> The <begin> and <end> values are XLogRecPtrs, not WAL filenames.
>
> If <begin> indicates the middle of the XLOG file, the file written to the
> standby is partial. Is this OK? After two server failed, the XLOG file
> including <begin> might still be required for crash recovery of the
> standby server. But, since it's partial, the crash recovery would fail.
> I think that any XLOG file should be written to the standby as it can
> be replayed by a normal recovery.

The standby can store the streamed WAL to files in pg_xlog of the
standby, to facilitate crash recovery, but it doesn't need to be exposed
in the protocol.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com