Unfortunately, we can't completely remove the ctx from git.Repository,
because the CatFileBatch still heavily depends on a parent context.
If we remove the Repository ctx, the CatFileBatch will become a mess and
create a lot of unnecessary git processes.
http://localhost:3000/-/admin/monitor/perftrace
* Before: open a repo home, dozens of git processes (duplicate cat-file)
* After: only a few (no duplicate cat-file)
by the way, remove some unnecessary "models" imports from model
migration package, fix migration test model init bug
(modelmigration/migrationtest/tests.go)
Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.
Also raise the minimum Git version required to 2.6.0 (released in 2015)
Replace #34651 and address more problems including fix framework bugs and changing to QueryInfo and QueryContent calls.
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Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
