Re: warning message in standby

On Tue, Jun 29, 2010 at 10:21 AM, Kevin Grittner
<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
>> ...with this patch, following the above, you get:
>>
>> FATAL:  invalid record in WAL stream
>> HINT:  Take a new base backup, or remove recovery.conf and restart
>> in read-write mode.
>> LOG:  startup process (PID 6126) exited with exit code 1
>> LOG:  terminating any other active server processes
>
> If someone is sloppy about how they copy the WAL files around, they
> could temporarily have a truncated file.

Can you explain the scenario you're concerned about in more detail?

> If we want to be tolerant
> of straight file copies, without a temporary name or location with a
> move on completion, we would need some kind of retry or timeout.  It
> appears that you have this hard-coded to five retries.  I'm not
> saying this is a bad setting, but I always wonder about hard-coded
> magic numbers like this.  What's the delay between retries?  How did
> you arrive at five as the magic number?

It's approximately the number Josh Berkus suggested in an email
upthread. In other words, SWAG.

There's not a fixed delay between retries - it represents the number
of times that we have either (a) streamed the relevant chunk from the
master via WALSender, or (b) retrieved the segment from the archive
with restore_command. The first retry CAN help, if WAL streaming from
master to standby was interrupted unexpectedly. AFAIK, the additional
retries after that are just paranoia, but I can't rule out the
possibility that I'm missing something, in which case we might have to
rethink the whole approach.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company