Mailing List Archive: Varnish: Dev

Compression in Varnish

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stas.semeniuta at gmail

Mar 20, 2012, 4:29 AM

Post #1 of 4 (388 views)
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Compression in Varnish

Hi, everyone

When looking through varnish code, I noticed, that Varnish uses it's own
libvgz to compress and uncompress data. As far as I understand, this libvgz
is actually a zlib. The question is, why zlib isn't used directly?
Also, I use zlib in a vmodule, and when this vmodule is loaded, functions,
which are really called, are ones from libvgz. After noticing this, I
switched zlib to libvgz, but inflate function reports Z_DATA_ERROR on
gzipped data. Other tools, which do gunzipping, successfully unzip this
data. Do I need to do something special to use libvgz functions, or it's
same, as zlib? I mean something like pass set up extra variables, or do
extra initialization. In case I do, what?

Thaks in advance, Stas

slink at schokola

Mar 23, 2012, 7:38 AM

Post #2 of 4 (377 views)
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Re: Compression in Varnish [In reply to]

Hi Stas,

we probably need phk's attention for the second part of the question, but here's
at least a first attempt.

> The question is, why zlib isn't used directly?

Because some subtle changes to zlib were needed to allow for an efficient
integration of (un)compression into Varnish.

> Do I need to do something special to use libvgz functions

-> phk

At any rate, you should not assume the libvgz interface to be stable.

Nils

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phk at phk

Mar 26, 2012, 12:02 AM

Post #3 of 4 (369 views)
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Re: Compression in Varnish [In reply to]

In message <CAKJRfiKHxAoo0Wm+C4Kt0K6XEkzgCiwgPwogkiOTskAQduR5uQ [at] mail>
, Stas Semeniuta writes:

>After noticing this, I
>switched zlib to libvgz, but inflate function reports Z_DATA_ERROR on
>gzipped data.

Can you send me an example of the data which fails ?

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk [at] FreeBSD | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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stas.semeniuta at gmail

Mar 27, 2012, 2:03 AM

Post #4 of 4 (366 views)
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Re: Compression in Varnish [In reply to]

>Can you send me an example of the data which fails ?

The problem was in my code, libvgz decompresses this data correctly. Sorry
for hasty conclusions about libvgz not working.

>Because some subtle changes to zlib were needed to allow for an efficient
>integration of (un)compression into Varnish.

So in case you use zlib directly, varnish performance will degrade? If it's
so, how much will it get worse?

Thanks in advance, Stas

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