Josh Berkus
wal_archive_policy and enable/disable archiving accordingly. This
parameter can only be changed at server start. (This is required
because
the initial step of archiving each xlog is performed by the backend;
if
this were changeable after boot, then it might be possible for an
individual backend to override the wal_archive_policy and choose not
to
archive - which would then effect the whole system and all users,
not
just the user making that choice). It is considered less desirable
to
Let me voice a real-world exception to this policy. Imagine that you are
running an OLAP or decision-support database that analyzes data coming
from
an external source. Once a day you load 250MB of data via COPY and then
does transformations on that data. While doing the load, you do *not*
want
the archiver running, as it would quickly fill up the WAL partition and
backlog the archive tape.
Under the proposed PITR spec, the only way to handle this would be to:
1) Full back up
2) Shut down PG
3) Restart PG without archiving
4) Load the data
5) Shut down PG again
6) Restart PG with archiving
7) Full back-up again.
DBAs would like it much more if starting/stopping the archiver was
possible
via a superuser (not regular user) GUC. This would allow a much faster
cycle:
1) Full back up
2) Stop archiving
3) Load the data
4) Restart archiving
5) Full back-up
The scenario you mention is what I'd like to do, but don't just yet see
how.

I'd welcome input on this point, since I don't fully understand GUCs:

Thinking about this:
1. Since the backends run XLogArchiveNotify(), they must all do so
identically. One slip invalidates all the work of all the others.
GUC Options are:
INTERNAL - not appropriate
POSTMASTER - what I originally envisaged, but not what you want
SIGHUP - seems to allow different parameter settings in each backend
BACKEND - not appropriate
SUSET - maybe what you're looking for???????
USERLIMIT - no
USERSET - absolutely no

2. Maybe have Postmaster run something every so often that looks for
full xlogs and then executes XLogArchiveNotify() for them?

Thoughts anyone?

Best Regards, Simon Riggs

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