[ python-Bugs-849046 ] gzip.GzipFile is slow

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Bugs item #849046, was opened at 2003-11-25 16:45
Message generated for change (Comment added) made by ronaldoussoren
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Category: Python Library
Group: Python 2.3
Status: Open
Resolution: None
Priority: 5
Submitted By: Ronald Oussoren (ronaldoussoren)
Assigned to: Nobody/Anonymous (nobody)
Summary: gzip.GzipFile is slow

Initial Comment:
gzip.GzipFile is significantly (an order of a magnitude) 
slower than using the gzip binary. I've been bitten by this 
several times, and have replaced "fd = gzip.open('somefile', 
'r')" by "fd = os.popen('gzcat somefile', 'r')" on several 
occassions.

Would a patch that implemented GzipFile in C have any 
change of being accepted?

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>Comment By: Ronald Oussoren (ronaldoussoren)
Date: 2003-11-25 22:03

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The files are created using GzipFile. That speed is acceptable 
because it happens in a batch-job, reading back is the problem 
because that happens on demand and a user is waiting for the 
results.

gzcat is a *uncompress* utility (specifically it is "gzip -dc"), the 
compression level is irrelevant for this discussion. 

The python code seems to do quite some string manipulation, 
maybe that is causing the slowdown (I'm using fd.readline() in a 
fairly tight loop). I'll do some profiling to check what is taking so 
much time.

BTW. I'm doing this on Unix systems (Sun Solaris and Mac OS X).

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Comment By: Jim Jewett (jimjjewett)
Date: 2003-11-25 18:35

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Which compression level are you using?

It looks like most of the work is already done by zlib (which is in C), but GzipFile defaults to compression level 9.  Many other zips (including your gzcat?) default to a lower (but much faster) compression level.  


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