On Thu, Sep 27, 2012 at 7:14 PM, Nguyen Thai Ngoc Duy <pclo...@gmail.com> wrote: > On Thu, Sep 27, 2012 at 10:51 PM, Shawn Pearce <spea...@spearce.org> 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. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
