At runtime the Clustrix monitor will save to an sqlite3
database information about detected nodes and delete that
information if a node disappears.
At startup, if the monitor fails to connect to a bootstrap
node, it will try to connect any of the persisted nodes and
start from there.
This means that in general it is sufficient if the Clustrix
monitor at the very first startup can connect to a bootstrap
node; thereafter it will get by even if the bootstrap node
would disappear for good.
In this context master should be interpreted as "can be read
and written to".
Marking them as master requires less changes in RWS to make it
usable with a Clustrix cluster.
Since the settings are now protected fields, all related functions were
moved inside the monitor class. mon_ping_or_connect_to_db() is now a method
of MXS_MONITORED_SERVER. The connection settings class is defined inside the
server since that is the class actually using the settings.
Once the monitor has been able to connect to a clustrix node
and obtain the clustrix nodes, it'll primarily use those nodes
when looking for a Clustrix node to be used as the "hub".
With this change it is sufficient (but perhaps unwise) to provide
a single node boostrap node in the configuration file.
Some other rearrangements and renamings of functions has also been
made.
From system.membership we can find out what server exist in the
cluster while system.nodeinfo contains information about those
servers. If a node goes down, it will disappear from system.nodeinfo,
but not from system.membership. Consequently, we must start from
system.membership and then fetch more information from system.nodeinfo.
Incidentally, a query like
SELECT ms.nid, ni.iface_ip
FROM system.membership AS ms
LEFT JOIN system.nodeinfo AS ni ON ms.nid=ni.nodeid;
should provide all information in one go, but it seems that such joins
are not supported on the system tables.
