Re: streaming header too small

On Wed, Feb 20, 2013 at 5:02 PM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> On 20.02.2013 17:53, Selena Deckelmann wrote:
>>
>> On Wed, Feb 20, 2013 at 6:23 AM, Magnus
>> Hagander<magnus(at)hagander(dot)net>wrote:
>>
>>> Selena, was this reasonably reproducible for you? Would it be possible to
>>> get a network trace of it to show of that's the kind of package coming
>>> across, or by hacking up pg_basebackup to print the exact position it was
>>> at when the problem occurred?
>>
>>
>> This is happening with a very busy 700 GB system, so I'm going to rule out
>> a network trace out for the moment. The error is occurring "sometime" in
>> the middle of the backup. Last time it was at least 30-40 minutes into a 2
>> hr backup.
>
>
> If you could pinpoint the WAL position where the error happens, that would
> already help somewhat. For starters, put pg_receivexlog to verbose mode, so
> that it will print a line after each WAL segment. If my theory is correct,
> the error should happen at xlogid boundaries, ie. just after finishing a WAL
> segment whose filename ends with "FE".

Your theory is correct, it happens at xlogid boundaries.

The missing information is that AFAICT it can only happen if
pg_basebackup is run against a slave, and never on the master.

I've applied a patch that just accepts this case, and ignores it.
Originally I had pg_basebackup write a warning in that case, but on
second thought I think that's just wrong - it will send out warning
messages in cases that are absolutely normal.

I'm not going to bother with a backend side patch, since this is
mostly harmless (it sends a single packet of an extra 25 bytes in
what's usually a large backup, so it doesn't matter), and it's all
gone in 9.3 anyway. And in 9.1 and earlier, the support isn't there.

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/