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MDEV-28929: Plan selection takes forever with MDEV-28852 ...
Part #2: Extend heuristic pruning to use multiple tables as the "Model tables". Before the patch, heuristic pruning uses only one "Model table": The table which had the best cost AND record became the "Model table". After that, if a table's cost and record were both worse than those of the Model Table, the table would be pruned away. This didn't work well when the first table (the optimizer sorts them by record_count) had low record_count but relatively high cost: nothing could be pruned afterwards. The patch adds the two additional "Model tables": one with the least cost and the other with the least record_count. (In both cases, a table can be pruned away if BOTH its cost and record_count are worse than those of a Model table) The new pruning is active when the number of tables to consider for the prefix is higher than @@optimizer_extra_pruning_depth. One can see the new pruning in the Optimizer Trace as - "pruned_by_heuristic":"min_record_count", or - "pruned_by_heuristic":"min_read_time". Old heuristic pruning shows as "pruned_by_heuristic":1.
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‎mysql-test/main/mysqld--help.result‎

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@@ -699,6 +699,10 @@ The following specify which files/extra groups are read (specified before remain
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max_connections*5 or max_connections + table_cache*2
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(whichever is larger) number of file descriptors
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(Automatically configured unless set explicitly)
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--optimizer-extra-pruning-depth=#
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If the optimizer needs to enumerate join prefix of this
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size or larger, then it will try agressively prune away
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the search space.
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--optimizer-max-sel-arg-weight=#
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The maximum weight of the SEL_ARG graph. Set to 0 for no
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limit
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old-mode UTF8_IS_UTF8MB3
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old-passwords FALSE
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old-style-user-limits FALSE
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optimizer-extra-pruning-depth 8
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optimizer-max-sel-arg-weight 32000
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optimizer-prune-level 2
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optimizer-search-depth 62

‎mysql-test/main/opt_trace.result‎

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@@ -6035,86 +6035,7 @@ t_outer_2.a in (select t_inner_3.a from t2 t_inner_3, t1 t_inner_4) {
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"rows_for_plan": 729,
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"cost_for_plan": 176.0410156,
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"semijoin_strategy_choice": [],
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"rest_of_plan": [
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{
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"plan_prefix": [
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"t_outer_1",
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"t_outer_2",
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"t_inner_1",
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"t_inner_3"
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],
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"get_costs_for_tables": [
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{
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"best_access_path": {
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"table": "t_inner_4",
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"considered_access_paths": [
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{
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"access_type": "scan",
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"resulting_rows": 3,
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"cost": 2.005126953,
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"chosen": true
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}
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],
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"chosen_access_method": {
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"type": "scan",
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"records": 3,
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"cost": 2.005126953,
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"uses_join_buffering": true
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}
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}
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},
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{
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"best_access_path": {
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"table": "t_inner_2",
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"considered_access_paths": [
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{
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"access_type": "scan",
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"resulting_rows": 9,
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"cost": 2.015380859,
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"chosen": true
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}
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],
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"chosen_access_method": {
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"type": "scan",
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"records": 9,
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"cost": 2.015380859,
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"uses_join_buffering": true
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}
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}
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}
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]
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},
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{
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"plan_prefix": [
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"t_outer_1",
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"t_outer_2",
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"t_inner_1",
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"t_inner_3"
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],
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"table": "t_inner_2",
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"rows_for_plan": 6561,
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"cost_for_plan": 1490.256396,
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"semijoin_strategy_choice": [],
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"pruned_by_cost": true,
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"current_cost": 1490.256396,
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"best_cost": 568.8615234
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},
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{
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"plan_prefix": [
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"t_outer_1",
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"t_outer_2",
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"t_inner_1",
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"t_inner_3"
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],
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"table": "t_inner_4",
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"rows_for_plan": 2187,
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"cost_for_plan": 615.4461426,
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"semijoin_strategy_choice": [],
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"pruned_by_cost": true,
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"current_cost": 615.4461426,
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"best_cost": 568.8615234
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}
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]
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"pruned_by_heuristic": "min_read_time"
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}
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]
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},
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"rows_for_plan": 729,
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"cost_for_plan": 172.4410156,
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"semijoin_strategy_choice": [],
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"rest_of_plan": [
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{
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"plan_prefix": [
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"t_outer_1",
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"t_inner_1",
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"t_outer_2",
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"t_inner_3"
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],
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"get_costs_for_tables": [
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{
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"best_access_path": {
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"table": "t_inner_4",
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"considered_access_paths": [
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{
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"access_type": "scan",
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"resulting_rows": 3,
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"cost": 2.005126953,
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"chosen": true
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}
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],
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"chosen_access_method": {
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"type": "scan",
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"records": 3,
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"cost": 2.005126953,
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"uses_join_buffering": true
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}
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}
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},
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{
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"best_access_path": {
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"table": "t_inner_2",
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"considered_access_paths": [
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{
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"access_type": "scan",
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"resulting_rows": 9,
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"cost": 2.015380859,
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"chosen": true
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}
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],
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"chosen_access_method": {
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"type": "scan",
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"records": 9,
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"cost": 2.015380859,
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"uses_join_buffering": true
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}
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}
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}
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]
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},
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{
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"plan_prefix": [
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"t_outer_1",
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"t_inner_1",
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"t_outer_2",
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"t_inner_3"
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],
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"table": "t_inner_2",
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"rows_for_plan": 6561,
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"cost_for_plan": 1486.656396,
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"semijoin_strategy_choice": [],
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"pruned_by_cost": true,
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"current_cost": 1486.656396,
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"best_cost": 565.2615234
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},
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{
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"plan_prefix": [
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"t_outer_1",
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"t_inner_1",
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"t_outer_2",
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"t_inner_3"
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],
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"table": "t_inner_4",
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"rows_for_plan": 2187,
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"cost_for_plan": 611.8461426,
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"semijoin_strategy_choice": [],
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"pruned_by_cost": true,
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"current_cost": 611.8461426,
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"best_cost": 565.2615234
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}
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]
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"pruned_by_heuristic": "min_read_time"
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}
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]
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},

‎mysql-test/suite/sys_vars/r/sysvars_server_embedded.result‎

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@@ -2252,6 +2252,16 @@ NUMERIC_BLOCK_SIZE 1
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ENUM_VALUE_LIST NULL
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READ_ONLY YES
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COMMAND_LINE_ARGUMENT REQUIRED
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VARIABLE_NAME OPTIMIZER_EXTRA_PRUNING_DEPTH
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VARIABLE_SCOPE SESSION
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VARIABLE_TYPE BIGINT UNSIGNED
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VARIABLE_COMMENT If the optimizer needs to enumerate join prefix of this size or larger, then it will try agressively prune away the search space.
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NUMERIC_MIN_VALUE 0
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NUMERIC_MAX_VALUE 62
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NUMERIC_BLOCK_SIZE 1
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ENUM_VALUE_LIST NULL
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READ_ONLY NO
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COMMAND_LINE_ARGUMENT REQUIRED
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VARIABLE_NAME OPTIMIZER_MAX_SEL_ARG_WEIGHT
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VARIABLE_SCOPE SESSION
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VARIABLE_TYPE BIGINT UNSIGNED

‎mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result‎

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@@ -2422,6 +2422,16 @@ NUMERIC_BLOCK_SIZE 1
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ENUM_VALUE_LIST NULL
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READ_ONLY YES
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COMMAND_LINE_ARGUMENT REQUIRED
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VARIABLE_NAME OPTIMIZER_EXTRA_PRUNING_DEPTH
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VARIABLE_SCOPE SESSION
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VARIABLE_TYPE BIGINT UNSIGNED
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VARIABLE_COMMENT If the optimizer needs to enumerate join prefix of this size or larger, then it will try agressively prune away the search space.
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NUMERIC_MIN_VALUE 0
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NUMERIC_MAX_VALUE 62
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NUMERIC_BLOCK_SIZE 1
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ENUM_VALUE_LIST NULL
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READ_ONLY NO
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COMMAND_LINE_ARGUMENT REQUIRED
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VARIABLE_NAME OPTIMIZER_MAX_SEL_ARG_WEIGHT
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VARIABLE_SCOPE SESSION
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VARIABLE_TYPE BIGINT UNSIGNED

‎sql/sql_class.h‎

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ulong net_retry_count;
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ulong net_wait_timeout;
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ulong net_write_timeout;
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ulong optimizer_extra_pruning_depth;
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ulong optimizer_prune_level;
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ulong optimizer_search_depth;
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ulong optimizer_selectivity_sampling_limit;

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