There are no masters or slaves in SolrCloud - it is fully distributed and
"master-free". Leaders are temporary and can vary over time.
The basic idea for quorum is to prevent "split brain" - two (or more)
distinct sets of nodes (zookeeper nodes, that is) each thinking they
constitute the authoritative source for access to configuration information.
The trick is to require (N/2)+1 nodes for quorum. For n=3, quorum would be
(3/2)+1 = 1+1 = 2, so one node can be down. For n=1, quorum = (1/2)+1 = 0 +
1 = 1. For n=2, quorum would be (2/2)+1 = 1 + 1 = 2, so no nodes can be
down. IOW, for n=2 no nodes can be down for the cluster to do updates.
-- Jack Krupansky
-----Original Message-----
From: Zhang, Lisheng
Sent: Thursday, July 11, 2013 9:28 AM
To: solr-user@lucene.apache.org
Subject: What happens in indexing request in solr cloud if Zookeepers are
all dead?
Hi,
In solr cloud latest doc, it mentioned that if all Zookeepers are dead,
distributed
query still works because solr remembers the cluster state.
How about the indexing request handling if all Zookeepers are dead, does
solr
needs Zookeeper to know which box is master and which is slave for indexing
to
work? Could solr remember master/slave relations without Zookeeper?
Also doc said Zookeeper quorum needs to have a majority rule so that we must
have 3 Zookeepers to handle the case one instance is crashed, what would
happen if we have two instances in quorum and one instance is crashed (or
quorum
having 3 instances but two of them are crashed)? I felt the last one should
take
over?
Thanks very much for helps, Lisheng
