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  1. Couchbase Server
  2. MB-23723

request_plus range queries with LIMIT are slow

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Details

    • Bug
    • Resolution: Fixed
    • Major
    • 5.0.0
    • 5.0.0
    • query
    • 4 data nodes, 1 query node, 1 index node

    Description

      Query:

      SELECT name, email FROM `bucket-1` WHERE capped_small > $1 ORDER BY capped_small LIMIT 10;

      Index:

      CREATE INDEX by_capped_small ON `bucket-1`(capped_small);

      There are 20M documents in the database.

      The rate of not_bounded queries is rather high. We can achieve to up 18K queries/sec in Spock.

      But if I change scan_consistency from not_bounded to request_plus, the throughput drops to ~100 in 4.6 and ~700 in Spock. Spock results are almost as bad as 4.5.0 numbers.

      From graphs I can see that cbq-engine receives way more items from 2i when scan_consistency is set to request_plus. That results in high CPU and memory usage, and also larger number of KV fetches.

      I wonder if we have any limitation in this area.

      See also http://showfast.sc.couchbase.com/#/timeline/Linux/n1ql/pagination

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            pavelpaulau Pavel Paulau (Inactive)
            pavelpaulau Pavel Paulau (Inactive)
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            Dates

              Created:
              Updated:
              Resolved:

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                PagerDuty