On 9/22/2020 7:26 PM, Jonathan Tan wrote: >> +incremental-repack:: >> + The `incremental-repack` job repacks the object directory >> + using the `multi-pack-index` feature. In order to prevent race >> + conditions with concurrent Git commands, it follows a two-step >> + process. > > [snip] > >> First, it deletes any pack-files included in the >> + `multi-pack-index` where none of the objects in the >> + `multi-pack-index` reference those pack-files; this only happens >> + if all objects in the pack-file are also stored in a newer >> + pack-file. Second, it selects a group of pack-files whose "expected >> + size" is below the batch size until the group has total expected >> + size at least the batch size; see the `--batch-size` option for >> + the `repack` subcommand in linkgit:git-multi-pack-index[1]. The >> + default batch-size is zero, which is a special case that attempts >> + to repack all pack-files into a single pack-file. > > This lacks the detail of what happens to the selected group of packfiles > (in the second step) - in particular, that a new packfile is created and > the MIDX is rewritten so that all references to the selected group are > updated to refer to the new packfile instead, thus making it possible to > delete the selected group of packfiles in a subsequent first step. All > this is explained in the documentation of git-multi-pack-index (expire > and repack), though, so it might be better to refer to that. E.g. Here is my attempt to incorporate your recommendations into this doc: incremental-repack:: The `incremental-repack` job repacks the object directory using the `multi-pack-index` feature. In order to prevent race conditions with concurrent Git commands, it follows a two-step process. First, it calls `git multi-pack-index expire` to delete pack-files unreferenced by the `multi-pack-index` file. Second, it calls `git multi-pack-index repack` to select several small pack-files and repack them into a bigger one, and then update the `multi-pack-index` entries that refer to the small pack-files to refer to the new pack-file. This prepares those small pack-files for deletion upon the next run of `git multi-pack-index expire`. The selection of the small pack-files is such that the expected size of the big pack-file is at least the batch size; see the `--batch-size` option for the `repack` subcommand in linkgit:git-multi-pack-index[1]. The default batch-size is zero, which is a special case that attempts to repack all pack-files into a single pack-file. > Do we need get_midx_filename() to be global? No, that does not appear to be important (to this patch). It _was_ necessary when doing the "verify, then delete if problematic" mode. Thanks for catching it now that it is not necessary. Thanks, -Stolee
