proposal to optimise the performance of the Jar utility

mike.skells at mike.skells at
Thu Apr 14 09:15:35 UTC 2011

Hi Mike & Sherman,
My mistake - not sure where I got that from

Sent from my BlackBerry® wireless device

-----Original Message-----
From: Mike Duigou <mike.duigou at>
Date: Wed, 13 Apr 2011 17:02:10 
To: Xueming Shen<xueming.shen at>
Cc: <mike.skells at>; core-libs-dev Libs<core-libs-dev at>
Subject: Re: proposal to optimise the performance of the Jar utility

On Apr 13 2011, at 16:22 , Xueming Shen wrote:

> On 04-13-2011 3:00 PM, Mike Duigou wrote:
>> Mike, can you share the results of performance testing at various compression levels? Is there much difference between the levels or an apparent "sweet spot"?
>> For low hanging fruit for jdk 7 it might be worth considering raising the default compression level from 5 to 6 (the zlib default). Raising the level from 5 to 6 entails (by today's
> Hi Mike,
> zlib1.2.3/zlib.h states the default is level 6.  I've not checked or run any test to verify if its
> implementation matches its docs, any reason you think zlib actually is using level 5 as
> default? I can take look into it further...

I was basing this on Mike Skells' earlier posting:

>>>> 1. Allowing the Jar utility to have other compression levels (currently it
>>>> allows default (5) only)

If it's using Z_DEFAULT_COMPRESSION then it's actually using 6 as you suggest.

Sorry for the confusion.


> ...
> ZEXTERN int ZEXPORT deflateInit OF((z_streamp strm, int level));
>     Initializes the internal stream state for compression. The fields
>   zalloc, zfree and opaque must be initialized before by the caller.
>   If zalloc and zfree are set to Z_NULL, deflateInit updates them to
>   use default allocation functions.
>     The compression level must be Z_DEFAULT_COMPRESSION, or between 0 and 9:
>   1 gives best speed, 9 gives best compression, 0 gives no compression at
>   all (the input data is simply copied a block at a time).
>   Z_DEFAULT_COMPRESSION requests a default compromise between speed and
>   compression (currently equivalent to level 6).
> ...

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