The master validity check now checks if the master is down. This requires
that the slave status is assigned even if no master is available.
The failover precondition is also fulfilled as long as one valid promotion
candidate is found. Previously a slave that didn't use GTID replication
appeared to prevent failover.
The command is saved in a function object which is read by the monitor
thread. This way, manual and automatic cluster modification commands are
ran in the same step of a monitor cycle.
This update required several modifications in related code.
This also applies to autoselect switchover. The disk space warning has the least
priority, as the other criteria could lead to replication failures. Also, print
the reason the new master was selected over the second best candidate.
This makes the code clearer and reduces race conditions, as the monitor
could be writing SERVER->status while a router is reading it. Also,
the time during which the SERVER struct is locked drops to a fraction.
Since monitors are now freed at MaxScale exit, the server data should be freed. Also,
gtid domain variables are now initialized with a common constant.
StartMonitor() now takes a MXS_MONITOR_INSTANCE and returns
true, if the monitor could be started and false otherwise.
So, the setup is such that in createInstance(), the instance
data is created and then using startMonitor() and stopMonitor()
the monitor is started/stopped. Finally in destroyInstance(),
the actual instance data is deleted.
CreateInstance() (renamed from initMonitor()) and destroyInstance()
(renamed from finishMonitor()) have now tentatively been
implemented for all monitors.
Next step is to
1) change the prototype of startMonitor() to
bool (*startMonitor)(MXS_SPECIFIC_MONITOR*,
const MXS_MONITOR_PARAMETER*);
and assume that mon->handle will always contain the
instance,
2) not delete any data in stopMonitor(),
3) add monitorCreateAll() that calls createInstance() for all
monitors (and call that in main()), and
4) add monitorDestroyAll() that calls destroyInstance() for
all monitors (and call that in main()).
The master down verification through slaves won't work with this commit. It needs to be
redesigned to handle multiple slave connections or removed. Also, only the first row of
slave status data is used by the monitor, so multiple slave connections are still
incorrectly handled.
Autoselection is allowed for current master only, or both current and new master.
Autoselection is not allowed for just the new master.
Also, do_switchover() writes to its parameters when autoselecting for
better error messages.
The old hkheartbeat variable was changed to the mxs_clock() function that
simply wraps an atomic load of the variable. This allows it to be
correctly read by MaxScale as well as opening up the possibility of
converting the value load to a relaxed memory order read.
Renamed the header and associated macros. Removed inclusion of the
heartbeat header from the housekeeper header and added it to the files
that were missing it.
