RE: What happens in indexing request in solr cloud if Zookeepers are all dead?
Thanks very much for your clear explanation! -Original Message- From: Jack Krupansky [mailto:j...@basetechnology.com] Sent: Thursday, July 11, 2013 1:55 PM To: solr-user@lucene.apache.org Subject: Re: What happens in indexing request in solr cloud if Zookeepers are all dead? Sorry, no updates if no Zookeepers. There would be no way to assure that any node knows the proper configuration. Queries are a little safer using most recent configuration without zookeeper, but update consistency requires accurate configuration information. -- Jack Krupansky -Original Message- From: Zhang, Lisheng Sent: Thursday, July 11, 2013 2:59 PM To: solr-user@lucene.apache.org Subject: RE: What happens in indexing request in solr cloud if Zookeepers are all dead? Yes, I should not have used word master/slave for solr cloud! So if all Zookeepers are dead, could indexing requests be handled properly (could solr remember the setting for indexing)? Thanks very much for helps, Lisheng -Original Message- From: Jack Krupansky [mailto:j...@basetechnology.com] Sent: Thursday, July 11, 2013 10:46 AM To: solr-user@lucene.apache.org Subject: Re: What happens in indexing request in solr cloud if Zookeepers are all dead? 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
Re: What happens in indexing request in solr cloud if Zookeepers are all dead?
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
RE: What happens in indexing request in solr cloud if Zookeepers are all dead?
Yes, I should not have used word master/slave for solr cloud! So if all Zookeepers are dead, could indexing requests be handled properly (could solr remember the setting for indexing)? Thanks very much for helps, Lisheng -Original Message- From: Jack Krupansky [mailto:j...@basetechnology.com] Sent: Thursday, July 11, 2013 10:46 AM To: solr-user@lucene.apache.org Subject: Re: What happens in indexing request in solr cloud if Zookeepers are all dead? 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
Re: What happens in indexing request in solr cloud if Zookeepers are all dead?
Sorry, no updates if no Zookeepers. There would be no way to assure that any node knows the proper configuration. Queries are a little safer using most recent configuration without zookeeper, but update consistency requires accurate configuration information. -- Jack Krupansky -Original Message- From: Zhang, Lisheng Sent: Thursday, July 11, 2013 2:59 PM To: solr-user@lucene.apache.org Subject: RE: What happens in indexing request in solr cloud if Zookeepers are all dead? Yes, I should not have used word master/slave for solr cloud! So if all Zookeepers are dead, could indexing requests be handled properly (could solr remember the setting for indexing)? Thanks very much for helps, Lisheng -Original Message- From: Jack Krupansky [mailto:j...@basetechnology.com] Sent: Thursday, July 11, 2013 10:46 AM To: solr-user@lucene.apache.org Subject: Re: What happens in indexing request in solr cloud if Zookeepers are all dead? 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
