From: Geoffrey Irving Date: Mon, 02 Jun 2008 16:26:52 GMT Subject: Re: [PATCH] Adding a cache of commit to patch-id pairs to speed up git-cherry Message-ID: <7f9d599f0806020926j7ac9fb12jefa5a14fe5708226@mail.gmail.com> In-Reply-To: On Mon, Jun 2, 2008 at 9:18 AM, Johannes Schindelin wrote: > Hi, > > On Mon, 2 Jun 2008, Geoffrey Irving wrote: > >> On Mon, Jun 2, 2008 at 8:37 AM, Johannes Schindelin >> 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. Geoffrey