spurious warnings about empty rbr buffer for update queries

[Seppo Jaakola]

Error log shows warnings like:

120504 11:01:01 [Warning] WSREP: empty rbr buffer, query: UPDATE `instance`
SET `instance_name` = 'Nagios Cygnus' WHERE `instance_id` = '1' LIMIT 1,

These can be false positives, and due to case where update matches some rows, buit update is not effective. i.e. row before image == row after image

=> change the condition for the warning more strict to filter out such non-effective update cases

[Seppo Jaakola (seppo-jaakola)]

Cannot reproduce this issue. Tested scenarios:

1. non effective update on table with PK
2. non effective update on table without PK
3. non effective transaction (set...reset)
4. voluntary transaction rollbacks
5. BF aborts (idle, exec, commit phases)

[Seppo Jaakola (seppo-jaakola)]

The application producing these is centreon 2.3.8. And problem has been diagnosed only with a private Solaris build.
I have not been able to reproduce this with Ubuntu build, at least so far.

[Seppo Jaakola (seppo-jaakola)]

bad diagnosis above, the problem happens with official 5.5.23-23.5 build.
Also Drupal (probably apache-solr module) used in master-slave mode generates such warnings

[Seppo Jaakola (seppo-jaakola)]

affected rows statistics cannot be trusted, demoted the warning to debug level and pushed in: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3756

[Seppo Jaakola (seppo-jaakola)]

ok, the plan is now to leave the message demoted to debug level for now, and design a comprehensive commit-time consistency assert in the future.