Обсуждение: [PERFORM] Can we activate WAL runtime?

prakash wrote:
> Hi All,   I am using postgres 8.2. I want to use Write Ahead Log (WAL)
> functionality to take a back up. I know one way to activate WAL is through
> updating postgres.conf file with archive_command. but how do I activate it on
> the server command line? Can we activate it runtime?

You may be able to reload the server (/etc/init.d/postgresql reload or 
pg_ctl reload) to activate WAL archiving. However, this thread suggests 
that it is, or was, only at server restart:

http://www.nabble.com/Enabling-archive_mode-without-restart-td20267884.html

It appears to depend on version, in that there are suggestions that in 
8.2 (which you're using) it can be set during a reload. There may be 
reasons why that was removed, though, so I wouldn't do anything without 
at least testing on a spare machine - and preferably without waiting for 
someone with a clue to chime in here.

Hmm, like Tom Lane did in that thread referenced above:

"... and affects a whole bunch of other behaviors too, in processes all
across the database that could not possibly adopt a new setting
synchronously.  That's exactly why it was made a postmaster-start option
to begin with.  Simon's given no argument at all why it would be safe to
flip it on-the-fly."

Again, though, that may be new in 8.3, I really would wait for some 
confirmation.

--
Craig Ringer