On Thu, Sep 27, 2012 at 9:33 PM, Shawn Pearce <spea...@spearce.org> wrote: >> I'd like to see some sort of extension mechanism like in >> $GIT_DIR/index, so that we don't have to increase pack index version >> often. > > This might be worthwhile. I dislike the way $GIT_DIR/index encodes > extensions. Forcing an extension to fully materialize itself to > determine its length so the length can be placed before the data is > painful to work with when writing the file out to disk. I would prefer > writing an index catalog at the trailer of the file. We already > require random access to the index file, so its possible for a reader > to read a fixed size trailer record that has the 2 SHA-1s we normally > end an index with, and an extension catalog footer that has a length > and CRC-32 of the catalog. The catalog would immediately appear before > the footer, so a reader can find the start of the extension catalog by > subtracting from the end of the file the catalog length and the file > footer and catalog footer lengths. The catalog can then supply a > starting offset for each extension section, and writers don't need to > predict in advance how much data they need to store. Readers trying to > use extensions aren't really hurt, Git already randomly seeks to read > the tail of an index file to compare the pack SHA-1 before assuming > the index is valid.
Yeah, that's exactly what I had in mind. But perhaps a separate file (or files?) may be better. On that point, should all extensions be in one new extra file, or one extension per file? I prefer all extensions in one file, so we only need a single additional stat() for extension check instead of probing for the entire pack-XXX.* range. In that case, the catalog trailer idea still applies. -- Duy -- 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
