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  1. MariaDB Server
  2. MDEV-383

Evaluate subquery predicates earlier or later depending on their SELECTIVITY

        Details

        • Type: Task
        • Status: Open
        • Priority: Minor
        • Resolution: Unresolved
        • Fix Version/s: 10.1
        • Component/s: None
        • Labels:

          Description

          (Based on conversation with Igor)
          There are a lot of subquery conditions out there that are inexpensive to
          evaluate and have good selectivity.

          If we just implement MDEV-83, we may get regressions. We need to take
          subquery condition's selectivity into account.

          It is difficult to get a meaningful estimate for an arbitrary, correlated
          subquery predicate.

          One possible solution is to measure selectivity during execution and reattach
          predicates on the fly.

          We don't want to change the query plan all the time, one way to dynamically
          move items between item trees is to wrap them inside Item_func_trig_cond so
          we can switch them on and off.

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                relates to

                Task - A task that needs to be done. MDEV-83 Cost-based choice for the pushdown of subqueries to joined tables

                • Minor - Minor loss of function, or other problem where easy workaround is present.
                • Stalled

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                    • Assignee:
                      Unassigned
                      Reporter:
                      psergey Sergei Petrunia
                    • Votes:
                      3 Vote for this issue
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                      Dates

                      • Created:
                        Updated: