Handle vdb restart order
------------------------
Key: SEQUOIA-947
URL: https://forge.continuent.org/jira/browse/SEQUOIA-947
Project: Sequoia
Type: Improvement
Components: Core, CLI Console
Versions: Sequoia 2.10.7
Reporter: Olivier Fambon
After a full vdb stop, i.e. a stop of all vdb-parts on all nodes, vdb-parts
should be reloaded in reverse order from shutdown. For example, if the shutdown
order was [EMAIL PROTECTED], then [EMAIL PROTECTED], the restart order should
be [EMAIL PROTECTED] then [EMAIL PROTECTED]
Upon miss-ordered vdb restart, the system currently behaves as follows:
- both vdb parts eventually load successfully modulo errors in full_cluster.log
- [EMAIL PROTECTED], the first vdb-part to be loaded, says nothing
- [EMAIL PROTECTED], the second vdb-part to be loaded, fails to perform
automatic recovery log resync
because its last clean shutdown checkpoint can not be found by the first part
(ERROR in full_cluster.log @node2)
- the recovery log on [EMAIL PROTECTED] is irremediably cleared.
The recovery log is cleared to prevent putting potentially ahead-of-date
backends online. Backends on the second vdb-part should then be restored to be
consistent with the one on the first part. If some write requests happened
while [EMAIL PROTECTED] was up and [EMAIL PROTECTED] was down, all the updates
for this time slice are lost.
It would be nice if the system could at least behave in such a way that
mistakes can be avoided.
This can be implemented by not allowing miss-ordered vdb-parts loading.
When shutting down, vdb parts note in their recovery log if they were the last
part to go down. Upon restart, the vdb-part will load only if it was the
last-man-down. For the initialization case, i.e. when starting a vdb for the
first time or when resetting a broken vdb, a special "init" flag must be
provided to the load command.
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