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

On Fri, Dec 12, 2014 at 03:27:33PM +0100, Andres Freund wrote:
> 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.

Well, I am just trying to understand when someone would benefit from WAL
compression. Are we saying it is only useful for non-SSL streaming?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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