1) No need to check server with only one team when teamRemover finds
a server team or machine team to remove
2) Fix optimalTeamCount counting in teamTracker
Which is an intermingling of what should be two commits:
1. Rely on TLogVersion instead of txsTags==0
2. Copy and index sharded txsTags between KCV and RV as txsTag when
configuring log_version 4->3.
The buggify was actually incorrect and broke an invariant, which I then
fixed on the other side, but this work was actually unneeded in total.
The real issue being fixed was returnIfBlock not sending an error, as
well as the other error cases.
Not only can we now compile this giant code block in parallel with the
rest of the code, we also no longer compile this giant function twice!
(Once for the master, once for the proxy.)
Because team remover does not remove a team if it causes 0 team per server.
So we currently disable the check until we have a better strategy to enforce the
desired number of teams.
This will not cause much problem in real situation, while having 0 team on a server
will make the server unable to host data, which is bad.
If the minimum number of teams of servers in a team is less than the
target value (desired_team_number_per_server * (teamSize + 1) / 2),
the team remover should not remove it. Otherwise, DD will oscillate in
building more teams and removing redundant teams.
Do not do consistency check for three_data_hall mode because when
machines are not evenly distributed across data halls, we will
need to build more teams than the total desired number to make sure
the number of teams per server is no less than the target value.
Do not overbuild teams because we may oscillate between building more teams and
removing the redundant teams. The oscillation happens when the machines are not
evenly distributed across availability zones.
For example, in three_data_hall mode, we have 1 machine in 1 data hall for 2 data halls.
We have 3 machines in the 3rd data hall. To build enough (and more teams) for servers
in the 3rd data hall, we will overbuild teams. However,
the teamRemover will remove those newly teams.
There were error cases that would cause a peek to terminate early or be
cancelled without sending anything to the next peek in line. We would
thus end up with the first peek in a sequence waiting on its future, and
nothing that exists that would send to that future.
Change to remove machine team with most machine teams, using the same
logic as the serverTeamRemover.
The featue is guarded by TR_FLAG_REMOVE_MT_WITH_MOST_TEAMS knob.
