[WIP] Partial clone fix #247
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While testing partial clone, I noticed some odd behavior. I was testing a way of running 'git init', followed by manually configuring the remote for partial clone, and then running 'git fetch'. Astonishingly, I saw the 'git fetch' process start asking the server for multiple rounds of pack-file downloads! When tweaking the situation a little more, I discovered that I could cause the remote to hang up with an error. Add two tests that demonstrate these two issues. In the first test, we find that when fetching with blob filters from a repository that previously did not have any tags, the 'git fetch --tags origin' command fails because the server sends "multiple filter-specs cannot be combined". In the second test, we see that a 'git fetch origin' request with several ref updates results in multiple pack-file downloads. This must be due to Git trying to fault-in the objects pointed by the refs. What makes this matter particularly nasty is that this goes through the do_oid_object_info_extended() method, so there are no "haves" in the negotiation. This leads the remote to send every reachable commit and tree from each new ref, providing a quadratic amount of data transfer! This test is fixed if we revert 6462d5e (fetch: remove fetch_if_missing=0, 2019-11-05), but that revert causes other test failures. The real fix will need more care. The tests are ordered in this way because if I swap the test order the tag test will succeed instead of fail. I believe this is because somehow we need the srv.bare repo to not have any tags when we clone, but then have tags in our next fetch. Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
When using partial-clone, do_oid_object_info_extended() can trigger a fetch for missing objects. This can be extremely expensive when asking for a tag or commit, as we are completely removed from the context of the missing object and thus supply no "haves" in the request. 6462d5e (fetch: remove fetch_if_missing=0, 2019-11-05) removed a global variable that prevented these fetches in favor of a bitflag. However, some object existence checks were not updated to use this flag. Update find_non_local_tags() to use OBJECT_INFO_SKIP_FETCH_OBJECT in addition to OBJECT_INFO_QUICK. The _QUICK option only prevents repreparing the pack-file structures. We need to be extremely careful about supplying _SKIP_FETCH_OBJECT when we expect an object to not exist due to updated refs. This resolves a broken test in t5616-partial-clone.sh. Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
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Just generating an installer. Will submit gitgitgadget#556 upstream.