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

> 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.