This ticket is to introduce a flag, which toggles the logic for bumping the collection's major version during split.
The flag should only be meaningful for the Config Server and should default to OFF (meaning the major version should not be bumped by default).
This flag should be present in 3.6, 4.0 and 4.2.
For 4.4, since the auto-splitter is running on the shards, this flag should be removed, along with the aforementioned logic for bumping the major version.
As part of a fix for a high CPU utilisation by the auto-splitter when writes are happening to the extreme chunks, we chose a solution, which erred on the side of correctness, with the reasoning that on most systems auto-splits are happening rarely and are not happening at the same time across all shards.
Under this solution, the collection's major version would be incremented only if a split happens at the shard, whose shardVersion == collectionVersion. Therefore, unless a split happens on this shard, all the other shards will just catch-up to its shard version and will then stop. This will repeat when the shard containing the collection version performs a split again, so the idea was that this will be amortised across the number of shards.
However, this logic seems to be causing more harm than good in the case of almost uniform writes across all chunks. If it is the case that all shards are doing splits almost in unison, under this fix there will constantly be a bump in the collection version, which means constant stalls due to StaleShardVersion.