non-uniform FK reference can cause slave crash

[Seppo Jaakola]

Slave node may crash due to foreign key processing problem, if following conditions are met:

1. foreign key constraint has been defined with CASCADE ON DELETE option
2. foreign key constraint has mixed NULL options in referencing columns
  (i.e. client column defined with NOT NULL option and parent column with NULL option)
3. slave is configured with multiple slave threads (wsrep_slave_threads > 1)
4. work load has conflicting DELETE operations for parent and child table

This problem was observed in Percona XtraDB Cluster installation, and reproduced with a regression test in Galera Cluster

[Seppo Jaakola (seppo-jaakola)]

actual fix pushed in wsrep-5.5 here: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3834

[Seppo Jaakola (seppo-jaakola)]

as a followup fix, in cascading delete processing, suppressing obsolete shared keys for parent table (which has exclusive key appended as well). Fix pushed in wsrep-5.5: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3836

[Seppo Jaakola (seppo-jaakola)]

Second followup fix, uses PK of child table when appending exclusive key for cascading delete operation. Fix pushed in wsrep-5.5: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3837

[Alex Yurchenko (ayurchen)]

fix released in 23.7.3

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXC-1273