Re: QuickLZ compression algorithm (Re: Inclusion in the PostgreSQL backend for toasting rows)

"Robert Haas" <robertmhaas@gmail.com> writes:
> The whole thing got started because Alex Hunsaker pointed out that his
> database got a lot bigger because we disabled compression on columns >
> 1MB.  It seems like the obvious thing to do is turn it back on again.

I suggest that before we make any knee-jerk responses, we need to go
back and reread the prior discussion.  The current 8.4 code was proposed
here:
http://archives.postgresql.org/pgsql-patches/2008-02/msg00053.php
and that message links to several older threads that were complaining
about the 8.3 behavior.  In particular the notion of an upper limit
on what we should attempt to compress was discussed in this thread:
http://archives.postgresql.org/pgsql-general/2007-08/msg01129.php

After poking around in those threads a bit, I think that the current
threshold of 1MB was something I just made up on the fly (I did note
that it needed tuning...).  Perhaps something like 10MB would be a
better default.  Another possibility is to have different minimum
compression rates for "small" and "large" datums.
        regards, tom lane