Re: Hot Backup with rsync fails at pg_clog if under load

> > Linas, could you capture the output of pg_controldata *and* increase the
> > log level to DEBUG1 on the standby? We should then see nextXid value of
> > the checkpoint the recovery is starting from.
>
> I'll try to do that whenever I'm in that territory again... Incidentally,
> recently there was a lot of unrelated-to-this-post work to polish things
up
> for a talk being given at PGWest 2011 Today :)
>
> > I also checked what rsync does when a file vanishes after rsync computed
the
> > file list, but before it is sent. rsync 3.0.7 on OSX, at least,
complains
> > loudly, and doesn't sync the file. It BTW also exits non-zero, with a
special
> > exit code for precisely that failure case.
>
> To be precise, my script has logic to accept the exit code 24, just as
> stated in PG manual:
>
> Docs> For example, some versions of rsync return a separate exit code for
> Docs> "vanished source files", and you can write a driver script to accept
> Docs> this exit code as a non-error case.

I also am running into this issue and can reproduce it very reliably. For
me, however, it happens even when doing the "fast backup" like so:
pg_start_backup('whatever', true)...my traffic is more write-heavy than
linas's tho, so that might have something to do with it. Yesterday it
reliably errored out on pg_clog every time, but today it is
failing sporadically on pg_subtrans (which seems to be past where the
pg_clog error was)....the only thing that has changed is that I've changed
the log level to debug1....I wouldn't think that could be related though.
I've linked the requested pg_controldata and debug1 logs for both errors.
Both links contain the output from pg_start_backup, rsync, pg_stop_backup,
pg_controldata, and then the postgres debug1 log produced from a subsequent
startup attempt.

pg_clog: http://pastebin.com/mTfdcjwH
pg_subtrans: http://pastebin.com/qAXEHAQt

Any workarounds would be very appreciated.....would copying clog+subtrans
before or after the rest of the data directory (or something like that) make
any difference?

Thanks!