[jira] [Commented] (CASSANDRA-6345) Endpoint cache invalidation causes CPU spike (on vnode rings?)

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6345?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13821532#comment-13821532 ] 

Jonathan Ellis commented on CASSANDRA-6345:
-------------------------------------------

Interesting.  Could we optimize cOTM instead?  That would definitely be the simplest solution.

E.g. it looks like TreeMultimap.putAll actuallys loop over each entry and calls put one at a time which is the worst-case scenario for binary tree rebalancing -- quadratic time.

> Endpoint cache invalidation causes CPU spike (on vnode rings?)
> --------------------------------------------------------------
>
>                 Key: CASSANDRA-6345
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6345
>             Project: Cassandra
>          Issue Type: Bug
>         Environment: 30 nodes total, 2 DCs
> Cassandra 1.2.11
> vnodes enabled (256 per node)
>            Reporter: Rick Branson
>
> We've observed that events which cause invalidation of the endpoint cache (update keyspace, add/remove nodes, etc) in AbstractReplicationStrategy result in several seconds of thundering herd behavior on the entire cluster. 
> A thread dump shows over a hundred threads (I stopped counting at that point) with a backtrace like this:
>         at java.net.Inet4Address.getAddress(Inet4Address.java:288)
>         at org.apache.cassandra.locator.TokenMetadata$1.compare(TokenMetadata.java:106)
>         at org.apache.cassandra.locator.TokenMetadata$1.compare(TokenMetadata.java:103)
>         at java.util.TreeMap.getEntryUsingComparator(TreeMap.java:351)
>         at java.util.TreeMap.getEntry(TreeMap.java:322)
>         at java.util.TreeMap.get(TreeMap.java:255)
>         at com.google.common.collect.AbstractMultimap.put(AbstractMultimap.java:200)
>         at com.google.common.collect.AbstractSetMultimap.put(AbstractSetMultimap.java:117)
>         at com.google.common.collect.TreeMultimap.put(TreeMultimap.java:74)
>         at com.google.common.collect.AbstractMultimap.putAll(AbstractMultimap.java:273)
>         at com.google.common.collect.TreeMultimap.putAll(TreeMultimap.java:74)
>         at org.apache.cassandra.utils.SortedBiMultiValMap.create(SortedBiMultiValMap.java:60)
>         at org.apache.cassandra.locator.TokenMetadata.cloneOnlyTokenMap(TokenMetadata.java:598)
>         at org.apache.cassandra.locator.AbstractReplicationStrategy.getNaturalEndpoints(AbstractReplicationStrategy.java:104)
>         at org.apache.cassandra.service.StorageService.getNaturalEndpoints(StorageService.java:2671)
>         at org.apache.cassandra.service.StorageProxy.performWrite(StorageProxy.java:375)
> It looks like there's a large amount of cost in the TokenMetadata.cloneOnlyTokenMap that AbstractReplicationStrategy.getNaturalEndpoints is calling each time there is a cache miss for an endpoint. It seems as if this would only impact clusters with large numbers of tokens, so it's probably a vnodes-only issue.
> Proposal: In AbstractReplicationStrategy.getNaturalEndpoints(), cache the cloned TokenMetadata instance returned by TokenMetadata.cloneOnlyTokenMap(), wrapping it with a lock to prevent stampedes, and clearing it in clearEndpointCache(). Thoughts?



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