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  1. Couchbase Server
  2. MB-42092

Remove hash detail stats from cbcollect

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    Description

      During qualification testing of 6.6.0 it was noted that memcached stats hash detail has a sizeable impact on server performance (ops/s).

      The exact cause of that slowdown has not been confirmed, but the belief is that given "hash" must traverse every item in each vBucket's HashTable and (while under lock) accumulate various stats including histograms of chain depth :-

      class HashTableDepthStatVisitor : public HashTableDepthVisitor {
      public:
          void visit(int bucket, int depth, size_t mem) {
              (void)bucket;
              // -1 is a special case for min.  If there's a value other than
              // -1, we prefer that.
              min = std::min(min == -1 ? depth : min, depth);
              max = std::max(max, depth);
              depthHisto.add(depth);
              size += depth;
              memUsed += mem;
          }
      

      While this is being investigated and improved, temporarily remove this stat call from cbcollect to avoid impacting normal operation in customer environments.

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          Activity

            Build couchbase-server-6.6.1-9144 contains ns_server commit a28eb8f with commit message:
            MB-42092: Remove hash details stats from cbcollect_info

            build-team Couchbase Build Team added a comment - Build couchbase-server-6.6.1-9144 contains ns_server commit a28eb8f with commit message: MB-42092 : Remove hash details stats from cbcollect_info

            Build couchbase-server-7.0.0-3536 contains ns_server commit a28eb8f with commit message:
            MB-42092: Remove hash details stats from cbcollect_info

            build-team Couchbase Build Team added a comment - Build couchbase-server-7.0.0-3536 contains ns_server commit a28eb8f with commit message: MB-42092 : Remove hash details stats from cbcollect_info

            Wayne Siu I'm fairly sure all the changes tracked by this ticket are in but will wait for James/Daniel to resolve the ticket.

            steve.watanabe Steve Watanabe added a comment - Wayne Siu I'm fairly sure all the changes tracked by this ticket are in but will wait for James/Daniel to resolve the ticket.
            owend Daniel Owen added a comment -

            Hi all, Apologies. All changes are in. I will mark as resolved.

            owend Daniel Owen added a comment - Hi all, Apologies. All changes are in. I will mark as resolved.
            tom.geri Tom Geri added a comment -

            Do we know if this issue affects previous versions or we have it under different ticket?

            tom.geri Tom Geri added a comment - Do we know if this issue affects previous versions or we have it under different ticket?
            owend Daniel Owen added a comment -

            Hi Tom Geri, I suspect other versions are affected but just not tracked for example
            just looked at 6.5.0 and we include ["hash", "detail"]

            http://src.couchbase.org/source/xref/6.5.0/ns_server/cbcollect_info#1323

            owend Daniel Owen added a comment - Hi Tom Geri , I suspect other versions are affected but just not tracked for example just looked at 6.5.0 and we include ["hash", "detail"] http://src.couchbase.org/source/xref/6.5.0/ns_server/cbcollect_info#1323

            Tom Geri / Daniel Owen Based on the linked Slack discussion I've added 6.5.x and linked the related issues.

            malarky Chris Malarky added a comment - Tom Geri / Daniel Owen Based on the linked Slack discussion I've added 6.5.x and linked the related issues.

            People

              owend Daniel Owen
              james.harrison James Harrison
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                Updated:
                Resolved:

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