Subject: Re: [PATCH v2 0/5] New hash table implementation

From: Karsten Blees <[email-masked]>
Date: Thu, 26 Sep 2013 15:55:52 +0200

Am 26.09.2013 12:16, schrieb Fredrik Gustafsson:
> On Tue, Sep 24, 2013 at 11:50:16AM +0200, Karsten Blees wrote:
>> Tests can be reproduced with 'time echo "perfhash[map] <method> 1000" | ./test-hashmap', see test-hashmap.c for definition of method flags.
> 
> So I'm still curious about the actual performance improvements for git.
> I runned git describe on the linux kernel with both the old hashmap and
> this new one:
> 

Performance was never the primary issue, the intention of the performance tests was to ensure that the new implementation doesn't *slow down* git.

>>From the original PATCH/RFC:
- O(1) remove
- builtin entry chaining
- ready-to-use FNV-1 hash functions
- unit test
- additions are ~twice as fast
- uses less memory

So, the new implementation allows us to get rid of workarounds such as the CE_UNHASHED flag, duplicate entry chaining code and hash_name() implementations. It also addresses the memory usage FIXME in hash.h.

The simplified API may help prevent bugs such as the broken entry chaining in name-hash.c (see commits 2548183, 395c735, 2092678).

Maybe we can also replace some of the custom hash table implementations in attr.c, decorate.c, fast-import.c and object.c (to name just a few...).