Re: Simplifying replication

> Please see
> http://archives.postgresql.org/pgsql-docs/2010-10/msg00038.php

Ye gods and little fishes!

You really want to talk arcane formulas.  I've re-read that
three times, and am still not sure that I could tell someone 
definitively how much disk space WAL needs for a given group of 
settings.  I'll also point out that that formula is not in our docs -- 
what's an appropriate location?

I think this needs to be corrected in 9.1, *even if it means breaking 
backwards compatibility*.

What would be sensible for DBAs is to have two settings:

max_wal_size
min_wal_size

These would be expresses in MB or GB and would be simple direct 
quantities, which our formulas would work backwards from.  max_wal_size 
would be a hard limit (i.e. Postgres would stop accepting writes if we 
hit it), and Admins would not be allowed to set min_wal_size to more 
than max_wal_size - 2.

Even better would be to replace min_wal_size with min_wal_time, which 
would set a time span for the oldest WAL segment to be kept (up to 
max_wal_size - 2).   Hmmm.  That doesn't seem that hard to implement. 
Is it?

(BTW, Robert, that e-mail is what I meant by "relationship")

--                                   -- Josh Berkus                                     PostgreSQL Experts Inc.                                     http://www.pgexperts.com