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  1. MariaDB Server
  2. MDEV-6430

It is impossible to see if "filesort with small limit" optimization was used

    Details

    • Type: Bug
    • Status: Closed (View Workflow)
    • Priority: Major
    • Resolution: Fixed
    • Affects Version/s: 10.0.12
    • Fix Version/s: 10.0.13
    • Component/s: None
    • Labels:
      None

      Description

      We've ported "filesort with small limit" optimization from mysql-5.6 into MariaDB 10.0.

      The problem is, it is impossible to see whether that optimization is used or not.

      In MySQL, one can check this as follows

      • set optimizer_trace=1
      • SELECT // need to run SELECT, not EXPLAIN
      • select * from optimizer_trace

      And then look for something like this:

            "join_execution": {
      ...
                  "filesort_priority_queue_optimization": {
                    "limit": 10,
                    "rows_estimate": 198717,
                    "row_size": 215,
                    "memory_available": 262144,
                    "chosen": true
                  },

      In MariaDB, there is no optimizer_trace, so one can't see it at all.

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            • Assignee:
              psergey Sergei Petrunia
              Reporter:
              psergey Sergei Petrunia
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              • Created:
                Updated:
                Resolved: