On Mon, Oct 1, 2012 at 8:49 AM, Shawn Pearce <spearce@xxxxxxxxxxx> wrote: > On Thu, Sep 27, 2012 at 7:14 PM, Nguyen Thai Ngoc Duy <pclouds@xxxxxxxxx> wrote: >> On Thu, Sep 27, 2012 at 10:51 PM, Shawn Pearce <spearce@xxxxxxxxxxx> wrote: >>> In Linus' Linux kernel tree there are currently about 323,178 commits. >>> If we store just the pre-parsed commit time as an int32 field this is >>> an additional 1.2 MiB of data in the pack-*.idx file, assuming we can >>> use additional data like pack offset position to correlate commit to >>> the parsed int. If we stored parent pointers in a similar way you >>> probably need at least 3.6 MiB of additional disk space on the index. >>> For example, use 12 bytes for each commit to store enough of the >>> parsed commit time to sort commits, and up to 2 parent pointers per >>> commit.... with a reserved magic value for octopus merges to mean the >>> commit itself has to be parsed to get the graph structure correct. >> >> This is much better than my naive approach (storing sha-1 and >> timestamps). We could use less space by storing parent pointer of >> non-merge commits only. Merge commits linux-2.6 is 6% the number of >> commits. git.git has higher percentage, 21%. I bet many projects do >> not merge as much and the number of merge commits is less than 5%. > > Some projects merge quite often. Android's frameworks/base repository > has a very large number of merges. Out of 79905 commits reachable from > the master branch, 65.3% are merges. So actually there are more merge > commits in the Android history than there are code commits. A cache of > only non-merges may be worthless on such a history. The good thing about these cache is it's configurable. Merge-preferred projects can choose to cache the first two parents. Non-merge projects can choose to cache just the first parent. We don't need a fixed format for both. -- Duy -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html