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  1. Cassandra
  2. CASSANDRA-12731

Remove IndexInfo cache from FileIndexInfoRetriever.




      Hi guys.
      In the patch of CASSANDRA-11206 , I found that FileIndexInfoRetriever allocates a (potentially very large) IndexInfo array (up to the number of IndexInfo in the RowIndexEntry has) as a cache in every single read path.

      After some experiments using LargePartitionTest on my MacBook, I got results that show that removing FileIndexInfoRetriever improves the performance for large partitions like below (latencies reduced by 41% and by 45%).

      // LargePartitionsTest.test_13_4G with cache by array
      INFO  [main] 2016-09-29 23:11:25,763 ?:? - SELECTs 1 for part=4194304k total=16384M took 94197 ms
      INFO  [main] 2016-09-29 23:12:50,914 ?:? - SELECTs 2 for part=4194304k total=16384M took 85151 ms
      // LargePartitionsTest.test_13_4G without cache
      INFO  [main] 2016-09-30 00:13:26,050 ?:? - SELECTs 1 for part=4194304k total=16384M took 55112 ms
      INFO  [main] 2016-09-30 00:14:12,132 ?:? - SELECTs 2 for part=4194304k total=16384M took 46082 ms

      Code is here (based on trunk)

      Heap memory usage during running LargePartitionsTest (except for 8G test) with array cache(original)

      Heap memory usage during running LargePartitionsTest (except for 8G test) without cache

      Of course, I have attempted to use some collection containers instead of a plain array. But I could not recognize great improvement enough to justify using these cache mechanism by them. (Unless I did some mistake or overlook about this test)

      LargePartitionsTest.test_12_2G SELECTs 1 (ms) SELECTs 2 (ms) Scan (ms)
      Original (array) 62736 48562 41540
      ConcurrentHashMap 47597 30854 18271
      ConcurrentHashMap 2nd trial 44036 26895 17443
      LinkedHashCache (capacity=16, limit=10, fifo) 1st 42668 32165 17323
      LinkedHashCache (capacity=16, limit=10, fifo) 2nd 48863 28066 18053
      LinkedHashCache (capacity=16, limit=16, fifo) 46979 29810 18620
      LinkedHashCache (capacity=16, limit=10, lru) 46456 29749 20311
      No Cache 47579 32480 18337
      No Cache 2nd trial 46534 27670 18700

      Code that I used for this comparison is here. LinkedHashCache is a simple fifo/lru cache that is extended by LinkedHashMap.
      Scan is a execution time to iterate through the large partition.

      So, in this issue, I'd like to propose to remove IndexInfo cache from FileIndexInfoRetriever to improve the performance on large partitions.


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          Yasuharu Goto
        2. screenshot-2.png
          142 kB
          Yasuharu Goto



            • Assignee:
              Yasuharu Yasuharu Goto
              Yasuharu Yasuharu Goto
              Yasuharu Goto
              Robert Stupp
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