setdiscovery: back out changeset 5cfdf6137af8 (issue5809) As explained in the bug report, this commit caused a performance regression. The problem occurs when the local repo has very many heads. Before 5cfdf6137af8, we used to get the remote's list of heads and if these heads mostly overlapped with the local repo's heads, we would mark these common heads as common, which would greatly reduce the size of the set of undecided nodes. Note that a similar problem existed before 5cfdf6137af8: If the local repo had very many heads and the server just had a few (or many heads from a disjoint set), we would do the same kind of slow discovery as we would with 5cfdf6137af8 in the case where local and remote repos share a large set of common nodes. For now, we just back out 5cfdf6137af8. We should improve the discovery in the "local has many heads, remote has few heads" case, but let's do that after backing this out. Differential Revision: https://phab.mercurial-scm.org/D2643