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  1. Cassandra
  2. CASSANDRA-6405

When making heavy use of counters, neighbor nodes occasionally enter spiral of constant memory consumpion



    • Bug
    • Status: Resolved
    • Normal
    • Resolution: Fixed
    • 2.1 beta2
    • None
    • None
    • RF of 3, 15 nodes.
      Sun Java 7 (also occurred in OpenJDK 6, and Sun Java 6).
      Xmx of 8G.
      No row cache.

    • Normal


      We're randomly running into an interesting issue on our ring. When making use of counters, we'll occasionally have 3 nodes (always neighbors) suddenly start immediately filling up memory, CMSing, fill up again, repeat. This pattern goes on for 5-20 minutes. Nearly all requests to the nodes time out during this period. Restarting one, two, or all three of the nodes does not resolve the spiral; after a restart the three nodes immediately start hogging up memory again and CMSing constantly.

      When the issue resolves itself, all 3 nodes immediately get better. Sometimes it reoccurs in bursts, where it will be trashed for 20 minutes, fine for 5, trashed for 20, and repeat that cycle a few times.

      There are no unusual logs provided by cassandra during this period of time, other than recording of the constant dropped read requests and the constant CMS runs. I have analyzed the log files prior to multiple distinct instances of this issue and have found no preceding events which are associated with this issue.

      I have verified that our apps are not performing any unusual number or type of requests during this time.

      This behaviour occurred on 1.0.12, 1.1.7, and now on 1.2.11.

      The way I've narrowed this down to counters is a bit naive. It started happening when we started making use of counter columns, went away after we rolled back use of counter columns. I've repeated this attempted rollout on each version now, and it consistently rears its head every time. I should note this incident does seem to happen more rarely on 1.2.11 compared to the previous versions.

      This incident has been consistent across multiple different types of hardware, as well as major kernel version changes (2.6 all the way to 3.2). The OS is operating normally during the event.

      I managed to get an hprof dump when the issue was happening in the wild. Something notable in the class instance counts as reported by jhat. Here are the top 5 counts for this one node:

      5967846 instances of class org.apache.cassandra.db.CounterColumn 
      1247525 instances of class com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap$WeightedValue 
      1247310 instances of class org.apache.cassandra.cache.KeyCacheKey 
      1246648 instances of class com.googlecode.concurrentlinkedhashmap.ConcurrentLinkedHashMap$Node 
      1237526 instances of class org.apache.cassandra.db.RowIndexEntry 

      Is it normal or expected for CounterColumn to have that number of instances?

      The data model for how we use counters is as follows: between 50-20000 counter columns per key. We currently have around 3 million keys total, but this issue also replicated when we only had a few thousand keys total. Average column count is around 1k, and 90th is 18k. New columns are added regularly, and columns are incremented regularly. No column or key deletions occur. We probably have 1-5k "hot" keys at any given time, spread across the entire ring. R:W ratio is typically around 50:1. This is the only CF we're using counters on, at this time. CF details are as follows:

          ColumnFamily: CommentTree
            Key Validation Class: org.apache.cassandra.db.marshal.AsciiType
            Default column value validator: org.apache.cassandra.db.marshal.CounterColumnType
            Cells sorted by: org.apache.cassandra.db.marshal.CompositeType(org.apache.cassandra.db.marshal.LongType,org.apache.cassandra.db.marshal.LongType,org.apache.cassandra.db.marshal.LongType)
            GC grace seconds: 864000
            Compaction min/max thresholds: 4/32
            Read repair chance: 0.01
            DC Local Read repair chance: 0.0
            Populate IO Cache on flush: false
            Replicate on write: true
            Caching: KEYS_ONLY
            Bloom Filter FP chance: default
            Built indexes: []
            Compaction Strategy: org.apache.cassandra.db.compaction.LeveledCompactionStrategy
            Compaction Strategy Options:
              sstable_size_in_mb: 160
                      Column Family: CommentTree
                      SSTable count: 30
                      SSTables in each level: [1, 10, 19, 0, 0, 0, 0, 0, 0]
                      Space used (live): 4656930594
                      Space used (total): 4677221791
                      SSTable Compression Ratio: 0.0
                      Number of Keys (estimate): 679680
                      Memtable Columns Count: 8289
                      Memtable Data Size: 2639908
                      Memtable Switch Count: 5769
                      Read Count: 185479324
                      Read Latency: 1.786 ms.
                      Write Count: 5377562
                      Write Latency: 0.026 ms.
                      Pending Tasks: 0
                      Bloom Filter False Positives: 2914204
                      Bloom Filter False Ratio: 0.56403
                      Bloom Filter Space Used: 523952
                      Compacted row minimum size: 30
                      Compacted row maximum size: 4866323
                      Compacted row mean size: 7742
                      Average live cells per slice (last five minutes): 39.0
                      Average tombstones per slice (last five minutes): 0.0

      Please let me know if I can provide any further information. I can provide the hprof if desired, however it is 3GB so I'll need to provide it outside of JIRA.


        1. threaddump.txt
          589 kB
          Jason Harvey

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              Unassigned Unassigned
              alienth Jason Harvey
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