Re: warning message in standby

On 11/06/10 07:18, Fujii Masao wrote:
> On Fri, Jun 11, 2010 at 1:01 AM, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com>  wrote:
>> We're talking about a corrupt record (incorrect CRC, incorrect backlink
>> etc.), not errors within redo functions. During crash recovery, a corrupt
>> record means you've reached end of WAL. In standby mode, when streaming WAL
>> from master, that shouldn't happen, and it's not clear what to do if it
>> does. PANIC is not a good idea, at least if the server uses hot standby,
>> because that only makes the situation worse from availability point of view.
>> So we log the error as a WARNING, and keep retrying. It's unlikely that the
>> problem will just go away, but we keep retrying anyway in the hope that it
>> does. However, it seems that we're too aggressive with the retries.
>
> Right. The attached patch calms down the retries: if we found an invalid
> record while streaming WAL from master, we sleep for 5 seconds (needs to
> be reduced?) before retrying to replay the record which is in the same
> location where the invalid one was found. Comments?

Hmm, right now it doesn't even reconnect when it sees a corrupt record
streamed from the master. It's really pointless to retry in that case,
reapplying the exact same piece of WAL surely won't work. I think it
should disconnect, and then retry reading from archive and pg_xlog, and
then retry streaming again. That's pretty hopeless too, but it's at
least theoretically possible that something went wrong in the
transmission and the file in the archive is fine.

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