If you run this test it fails and you can see this exception in the console:

42071 ERROR (OverseerThreadFactory-6-thread-2-processing-n:127.0.0.1:49954_yd_dma%2Fkz) [n:127.0.0.1:49954_yd_dma%2Fkz    ] o.a.s.c.OverseerCollectionMessageHandler Error executing split operation for collection: shardSplitWithRule parent shard: shard1
java.lang.NullPointerException
	at org.apache.solr.cloud.rule.Rule.getNumberOfNodesWithSameTagVal(Rule.java:166)
	at org.apache.solr.cloud.rule.Rule.tryAssignNodeToShard(Rule.java:128)
	at org.apache.solr.cloud.rule.ReplicaAssigner.tryAPermutationOfRules(ReplicaAssigner.java:249)
	at org.apache.solr.cloud.rule.ReplicaAssigner.tryAllPermutations(ReplicaAssigner.java:201)
	at org.apache.solr.cloud.rule.ReplicaAssigner.getNodeMappings0(ReplicaAssigner.java:173)
	at org.apache.solr.cloud.rule.ReplicaAssigner.getNodeMappings(ReplicaAssigner.java:134)
	at org.apache.solr.cloud.Assign.getNodesViaRules(Assign.java:215)
	at org.apache.solr.cloud.Assign.getNodesForNewReplicas(Assign.java:178)
	at org.apache.solr.cloud.OverseerCollectionMessageHandler.addReplica(OverseerCollectionMessageHandler.java:2164)
	at org.apache.solr.cloud.OverseerCollectionMessageHandler.splitShard(OverseerCollectionMessageHandler.java:1388)
	at org.apache.solr.cloud.OverseerCollectionMessageHandler.processMessage(OverseerCollectionMessageHandler.java:236)
	at org.apache.solr.cloud.OverseerTaskProcessor$Runner.run(OverseerTaskProcessor.java:433)
	at org.apache.solr.common.util.ExecutorUtil$MDCAwareThreadPoolExecutor$1.run(ExecutorUtil.java:231)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

Thanks a lot Shai Erera I shall fix this right away

summary of changes:

• ReplicaAssigner should only lookup tags for nodes participating in selection. This is to avoid the NPE.
• splitShard() preassigns nodes and the assignment is done without using the ReplicaAssigner .This means , rules don't kick in when nodes are assigned in splitshard. In this patch, the preassigning is done using the rules , if they exist

Shalin Shekhar Mangar I would like you to take a look at the changes made to splitShard()

Thanks Noble.

+      List<String> subSliceNames =  new ArrayList<>();
+      for (int i = 0; i < subSlices.size(); i++) subSliceNames.add(slice + "_" + i);

This seems redundant because the "subSlices" list already has all the sub-slice names.

The rest looks good!

thanks

Commit 0cd24c5d08678a4cc883381d54089f62d0978b4d in lucene-solr's branch refs/heads/master from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=0cd24c5 ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

Commit 201b8b02a47ccbc7d08222e11b0a3d54f63ce90f in lucene-solr's branch refs/heads/branch_6x from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=201b8b0 ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

Commit 89524d917adc02018f277df56553546fd11fdf77 in lucene-solr's branch refs/heads/branch_6x from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=89524d9 ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

Commit b8183c808083fa206fbf5a0bec76807496fec162 in lucene-solr's branch refs/heads/branch_6_0 from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=b8183c8 ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

Commit d0de8cf8733662999e0dcd08cb07445b35632a9d in lucene-solr's branch refs/heads/branch_6_0 from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=d0de8cf ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

test failure caused by this fix
http://jenkins.thetaphi.de/job/Lucene-Solr-6.x-Linux/15/testReport/org.apache.solr.cloud/CollectionTooManyReplicasTest/testDownedShards/

This is marked as fixed in 6.0, but should it also be marked for 6.1(since it's also committed to 6x)?

What about master – was it not committed to master too? Does it not affect master?

And lastly, in case we will have a 5.5.1, is this considered a bugfix that we'll want to backport?

It's fixed on all three. So, isn't it implicit that stuff fixed in 6.0 is fixed in all releases that come after 6.0?

5.5.1 makes sense because it is a release prior to 6.0

We usually set the fix version to be e.g. "5.5" and "trunk/master".

Cause there are issues that are fixed only in a specific version, e.g. if they only affect that version.

I guess this should go to the 5.5 branch as well right away. Just in case there is a 5.5.1

Commit c17f80a7a22a4215ebcfe08939b6c0acc30df7c2 in lucene-solr's branch refs/heads/branch_5_5 from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=c17f80a ]

SOLR-8728

Commit 4faadb625e91b8ef323724855748258570137084 in lucene-solr's branch refs/heads/branch_5_5 from Noble Paul
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=4faadb6 ]

SOLR-8728: ReplicaAssigner throws NPE when a partial list of nodes are only participating in replica
placement. splitshard should preassign nodes using rules, if rules are present

Noble, this was committed to branch_5_5 but seems like you missed the change log entry.

Reopening to add the change log entry to branch_5_5.

branch_5x

commit 07f9cf8aee3523a22c92923f9d4e46a297efc455
Author: anshum <anshum@apache.org>
Date:   Thu Apr 21 15:59:25 2016 -0700

    SOLR-8728: Add missing change log entry for 5.5.1

branch_5_5

commit 5601f839c5001b1c2cce44b3b6349b1c1de23230
Author: anshum <anshum@apache.org>
Date:   Thu Apr 21 15:59:25 2016 -0700

    SOLR-8728: Add missing change log entry for 5.5.1

Manually correcting fixVersion per Step #S5 of LUCENE-7271