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Re: warm standby with WAL shipping

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Greg Smith wrote:
On Thu, 4 Jun 2009, Geoffrey wrote:

For now, I'm still looking at the other tools as well as attempting to verify that my current solution doesn't miss any 'little issues.'

The main thing you want to test out are that it acts sanely when the network connection to the destination server is out, and that it doesn't go insane if either the source or destination server run out of disk space. You should simulate both of those things.

This has not happened as of yet, part of the test suite though.

The important thing is to validate your script cannot say you've processed an archive file until you're absolutely positive it's stored somewhere safe. It's really not that hard. If you've got practice writing robust system scripts already, and it sounds like you do, I wouldn't hesitate to use a homegrown solution here instead of walmgr/pitrtools as long as you've done the tests I outline here.

I wrote a language parser in AWK years ago... ;) (that was ugly)

I assume a script that pulls the logs to the warm standby and then calls pg_standby.

The way you say this makes me think you haven't really absorbed how pg_standby works yet. You don't call it; the database recovery script does. Your program's interaction with it is merely to drop files into the place it expects them to be (atomically), it's a polling solution that alternates between looking for files there/applying them to the database/sleeping when there's no more left.

The script I mention above would be the recovery script. Since, as I understand pg_standby, looks for files locally, then my restore script would have to pull the files from the remote machine and drop them somewhere where pg_standby would be looking for them. That's my thought anyway.

If you've already gone to the trouble of writing all the pieces here yourself, it really shouldn't be difficult to yank out the parts pg_standby does and use it for those instead. There's a few things in there you'll have a hard time implementing yourself that probably aren't even on your radar yet, but are nonetheless important. Being able to keep standby disk usage pruned easily with the restartwalfile feature comes to mind, that one is a subtle problem that doesn't sneak up on you until you've been in production a while.

Still studying the pg_standby code. ;)

--
Until later, Geoffrey

Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety.
 - Benjamin Franklin

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