[doc] wsrep_sst_donor can be overridden by IST preference

[Jay Janssen]

Newer versions of Galera take into account IST possibility when selecting a donor (by checking the gcache contents). I discovered that even if you select an explicit wsrep_sst_donor, Galera will still choose a different donor if our selection cannot IST.

This behavior could be arguably a bug, but either way we should document its behavior properly in the manual (it is not).

[Raghavendra D Prabhu (raghavendra-prabhu)]

Yes, that has been the behavior since Galera 3.5 when smart donor selection was introduced. It applies to State transfer in general now, and so wsrep-sst-donor is also affected.

[Alexey Zhebel (alexey-zhebel)]

This page mentions that the wsrep-sst-donor variable takes both SST and IST into account: https://www.percona.com/doc/percona-xtradb-cluster/5.7/wsrep-system-index.html#wsrep_sst_donor

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXC-1117