Re: [PATCH] Adding a cache of commit to patch-id pairs to speed up git-cherry

> Hi,
>
> On Mon, 2 Jun 2008, Geoffrey Irving wrote:
>
>> On Mon, Jun 2, 2008 at 9:18 AM, Johannes Schindelin
>> <Johannes.Schindelin@gmx.de> wrote:
>>
>> > On Mon, 2 Jun 2008, Geoffrey Irving wrote:
>> >
>> >> On Mon, Jun 2, 2008 at 8:37 AM, Johannes Schindelin
>> >> <Johannes.Schindelin@gmx.de> wrote:
>> >>
>> >> > Another issue that just hit me: this cache is append-only, so if it
>> >> > grows too large, you have no other option than to scratch and
>> >> > recreate it. Maybe this needs porcelain support, too?  (git gc?)
>> >>
>> >> If so, the correct operation is to go through the hash and remove
>> >> entries that refer to commits that no longer exist.  I can add this
>> >> if you want.  Hopefully somewhere along the way git-gc constructs an
>> >> easy to traverse list of extant commits, and this will be
>> >> straightforward.
>> >
>> > I don't know... if you have created a cached patch-id for every commit
>> > (by mistake, for example) and do not need it anymore, it might make
>> > git-cherry substantially faster to just scrap the cache.
>>
>> Well, ideally hash maps are O(1), but it could be a difference between a
>> "compare 40 bytes" constant and a "read a 4k block into memory"
>> constant, so in practice yes.  Scrapping it entirely will also make the
>> implementation much simpler.
>>
>> It seems a little sad to wipe all that effort each time, but
>> regenerating the cache is likely to be less expensive than a git-gc, so
>> it shouldn't change any amortized complexities.
>
> Well, how about only scrapping the cache if it is older than, say, 2
> weeks, and is larger than, say, 200kB?  That should help.