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Re: Unexpected WAL-archive restore behaviour

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On 02/18/2017 10:01 PM, Nikolay Petrov wrote:
Hot standby server was started with new recovery.conf, reached
consistent recovery state and resumed to restore WAL segments from
archive. When couple of next wal segments became unavailable slave
server just "skipped" them, instead to start streaming WAL from
primary:

What do you mean by "became unavailable"? The restore_command may be called for segments that do not exist - that's expected, and I suspect the "gzip: stdin: unexpected end of file" error messages are caused by that.

Then, on the next try, that WAL segment probably existed, so it got restored. It's difficult to say what actually happened, because you've only posted doctored log - for example nowhere in the log is a message that the standby started streaming from the primary, i.e. something like this:

LOG:  started streaming WAL from primary at 18/DE000000 on timeline 1

But maybe not - it's possible this happening because the archive and restore commands are not atomic. E.g. let's say the restore_command gets executed while the WAL segment is still being archived. In that case it'll find an incomplete gzip archive, will try to decompress it, and will fail with exactly the same ('unexpected end of file') error.

So I think you should read the docs about archive/restore command requirements [1] and maybe also the wiki page about setting warm standby [2]:

[1] https://www.postgresql.org/docs/9.6/static/continuous-archiving.html

[2] https://wiki.postgresql.org/wiki/Warm_Standby

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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