Ed W wrote:
> Marcus Bointon wrote:
>> I have a circular replication setup that I want to stop, leaving just
>> one master. The (irreparably out of sync) second master has been
>> stopped for a while, and I want to abandon all changes that are
>> pending for it, wipe any pending logs, remove its databases prior to
>> rebuilding it. How do I safely deactivate secondary master references
>> on the primary? On the primary master I can do "stop slave", but I
>> want to make sure that it won't attempt to reconnect to the secondary
>> master if I restart it and won't execute functions from the secondary
>> that are part of the cleanup process (which could be fatal to the
>> real DB).
>
> This is a bit late, but I have had a lot of success using Maatkit from
> http://www.xaprb.com/
>
> The basic idea is that you keep replication going at all costs, detect
> it going out of sync using his rather clever table-checksum routines,
> then carefully resync the servers using his rather clever resync
> routines. By using "replace into" the point is that you can create a
> transaction which will replicate out and fix your servers and bring
> them back into sync again.
>
> Works very well for me. The use of replication to do the checksums is
> completely inspired also! Works fine for multi-master replication as
> well
My experience with maatkit, especially after running it after doing a
'repair table' is that it's pretty one-sided
and you might need to use the --print option to mk-table-sync before
actually running it a full strength.
Consider multi-masters A, B. You get application warnings that
B:bigtable is missing entries and has entries not on A:bigtable. You
look closer and find that A:bigtable reports 'crashed'. You've repaired
A:bigtable. That repair found shortened records and deleted them. If you
run mk-table-sync A B now, to replace the entries missing on B:bigtable,
B:bigtable will also lose the shortened records deleted from A:bigtable.
This whole situation started because replication behavior can seem to
become undefined when a table gets marked as crashed.
I do not know of a way to "Union" missing results with mk-table-sync,
because it certainly would be useful to keep the data in both tables. To
do that you'd have to query with 'mk-table-sync --print A B' then from
the other direction 'mk-table-sync --print B A' and then reconcile the
records.
Jed
