Deleting repositories will trigger an expensive but useless disconnect from its pool repository
We have recently seen an incident where DisconnectGitAlternates was invoked on some repositories that were about to be deleted. This RPC may in its current iteration be extremely expensive due to our use of git fsck --connectivity-only
, which we have seen to allocate about 80GB of RAM in some specific repositories. While that is a bug in Gitaly that we ought to fix, it's puzzling that we try to disconnect the repository from its alternate in the first place because all cases where we have seen this to happen it was for repositories that were about to be deleted.
We should likely drop the logic to disconnect Git alternates for repositories that are about to be deleted given that this is a wasted effort in the first place as it only changes the pool member, but never the pool itself.