| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Rahila Syed <rahilasyed90(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [REVIEW] Re: Compression of full-page-writes |
| Date: | 2014-12-12 14:27:33 |
| Message-ID: | 20141212142732.GJ31413@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2014-12-12 09:24:27 -0500, Bruce Momjian wrote:
> On Fri, Dec 12, 2014 at 03:22:24PM +0100, Andres Freund wrote:
> > > Well, the larger question is why wouldn't we just have the user compress
> > > the entire WAL file before archiving --- why have each backend do it?
> > > Is it the write volume we are saving? I though this WAL compression
> > > gave better performance in some cases.
> >
> > Err. Streaming?
>
> Well, you can already set up SSL for compression while streaming. In
> fact, I assume many are already using SSL for streaming as the majority
> of SSL overhead is from connection start.
That's not really true. The overhead of SSL during streaming is
*significant*. Both the kind of compression it does (which is far more
expensive than pglz or lz4) and the encyrption itself. In many cases
it's prohibitively expensive - there's even a fair number on-list
reports about this.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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