Sergei Petrunia 43c5d1303f MDEV-35958 Cost estimates for materialized derived tables are poor ...

Backport of commit 74f70c3944 to 10.11.
The new logic is disabled by default, to enable, use
optimizer_adjust_secondary_key_costs=fix_derived_table_read_cost.

== Original commit comment ==
Fixed costs in JOIN_TAB::estimate_scan_time() and HEAP

Estimate_scan_time() calculates the cost of scanning a derivied table.
The old code did not take into account that the temporary table heap table
may be converted to Aria.

  Things fixed:
  - Added checking if the temporary tables data will fit in the heap.
    If not, then calculate the cost based on the designated internal
    temporary table engine (Aria).
  - Removed MY_MAX(records, 1000) and instead trust the optimizer's
    estimate of records. This reduces the cost of temporary tables a bit
    for small tables, which caused a few changes in mtr results.
  - Fixed cost calculation for HEAP.
  - HEAP costs->row_next_find_cost was not set. This does not affect old
    costs calculation as this cost slot was not used anywhere.
    Now HEAP cost->row_next_find_cost is set, which allowed me to remove
    some duplicated computation in ha_heap::scan_time()

2025-02-10 21:14:01 +02:00

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