Simon Riggs wrote:
On Fri, 2007-03-30 at 16:34 -0400, Tom Lane wrote:
"Simon Riggs" <[EMAIL PROTECTED]> writes:
2. pg_stop_backup() should wait until all archive files are safely
archived before returning
Not sure I agree with that one.  If it fails, you can't tell whether the
action is done and it failed while waiting for the archiver, or if you
need to redo it.

There's a slight delay between pg_stop_backup() completing and the
archiver doing its stuff. Currently if somebody does a -m fast straight
after the pg_stop_backup() the backup may be unusable.

We need a way to plug that small hole.

I suggest that pg_stop_backup() polls once per second until
pg_xlog/archive_status/LOG.ready disappears, in which case it ends
successfully. If it does this for more than 60 seconds it ends
successfully but produces a WARNING.

I fear that ending sucessfully despite having not archived all wals
will make this feature less worthwile. If a dba knows what he is
doing, he can code a perfectly safe backup script using 8.2 too.
He'll just have to check the current wal position after pg_stop_backup(),
(There is a function for that, right?), and wait until the corresponding
wal was archived.

In realitly, however, I feare that most people will just create a script
that does 'echo "select pg_stop_backup | psql"' or something similar.
If they're a bit more carefull, they will enable ON_ERROR_STOP, and check
the return value of pgsql. I believe that those are the people who would
really benefit from a pg_stop_backup() that waits for archiving to complete.
But they probably won't check for WARNINGs.

Maybe doing it the other way round would be an option?
pg_stop_backup() could wait for the archiver to complete forever, but
spit out a warning every 60 seconds or so "WARNING: Still waiting
for wal archiving of wal ??? to complete". If someone really wants
a 60-second timeout, he can just use statement_timeout.

Anyway, just my 0.02 eurocents, maybe I'm totally mistaken about the
postgresql dba's out there...

greetings, Florian Pflug

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