Re: WAL file location

Tom Lane wrote:
> Thomas Lockhart <lockhart@fourpalms.org> writes:
> > I've developed patches to be able to specify the location of the WAL
> > directory, with the default location being where it is now. The patches
> > define a new environment variable PGXLOG (a la PGDATA) and postmaster,
> > postgres, initdb and pg_ctl have been taught to recognize a new command
> > line switch "-X" a la "-D".
> 
> Uh ... if I randomly modify PGXLOG and restart the postmaster, what
> happens?  Unless you've added code to *move* pg_xlog, this doesn't seem
> like a good idea.
> 
> More generally, I do not like depending on postmaster environment
> variables --- our experience with environment variables for database
> locations has been uniformly bad, and so ISTM that extending that
> mechanism into pg_xlog is exactly the wrong direction to head.
> 
> The current mechanism for moving pg_xlog around is to create a symlink
> from $PGDATA/pg_xlog to someplace else.  I'd be all in favor of creating
> some code to help automate moving pg_xlog that way, but I don't think
> introducing an environment variable will improve matters.

100% agree.

> > I'm intending to head towards finer control of locations of tables and
> > indices next by implementing some notion of named storage area, perhaps
> > including the "tablespace" nomenclature though it would not be the same
> > thing as in Oracle since it would not be fixed size but more akin to the
> > "secondary locations" that we support now for entire databases.
> 
> The existing secondary-location mechanism is horrible.  Please do not
> emulate it...

200% agree.  ;-)

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