Re: [REVIEW] Re: Compression of full-page-writes

On 12 December 2014 at 18:04, Bruce Momjian <bruce@momjian.us> wrote:

> Well, it seems we need to see some actual cases where compression does
> help before moving forward.  I thought Amit had some amazing numbers for
> WAL compression --- has that changed?

For background processes, like VACUUM, then WAL compression will be
helpful. The numbers show that only applies to FPWs.

I remain concerned about the cost in foreground processes, especially
since the cost will be paid immediately after checkpoint, making our
spikes worse.

What I don't understand is why we aren't working on double buffering,
since that cost would be paid in a background process and would be
evenly spread out across a checkpoint. Plus we'd be able to remove
FPWs altogether, which is like 100% compression.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services