[issue3376] rebuilding the tags cache is slow in a big repo

[Bryan O'Sullivan]

New submission from Bryan O'Sullivan <bos at serpentine.com>:

This has a simple test case:

   cd linux-2.6
   rm -f .hg/cache/tags
   hg --time tip

I just sent some patches to the list that partially address this by moving 
revlog.headrevs into parsers.c.

In the linux-2.6 tree, the headrevs patch improves time from 0.8 seconds to 
0.3.

Things are less rosy elsewhere - I have another repo with 330,000 commits, 
where the headrevs patch improves time from 2.2 to 1.6 seconds. The profile 
of the remaining time is similar to the linux-2.6 case - it's reconstructing 
a revision, and spending a lot of time in zlib.decompress.

----------
messages: 19637
nosy: bos
priority: bug
status: unread
title: rebuilding the tags cache is slow in a big repo

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