planner: add hint support for optimizer cost factors (#60558) (#61904)

ref #60357

Author: ti-chi-bot

pkg/planner/core/casetest/hint/BUILD.bazel

@@ -9,7 +9,7 @@ go_test(
     ],
     data = glob(["testdata/**"]),
     flaky = True,
-    shard_count = 8,
+    shard_count = 9,
     deps = [
         "//pkg/config",
         "//pkg/domain",

pkg/planner/core/casetest/hint/hint_test.go

@@ -16,6 +16,7 @@ package hint
 
 import (
 	"context"
+	"strconv"
 	"testing"
 
 	"github.com/pingcap/tidb/pkg/domain"
@@ -341,3 +342,90 @@ func TestQBHintHandlerDuplicateObjects(t *testing.T) {
 	tk.MustQuery("EXPLAIN WITH t AS (SELECT /*+ inl_join(e) */ em.* FROM t_employees em JOIN t_employees e WHERE em.store_id = e.department_id) SELECT * FROM t;")
 	tk.MustQuery("show warnings").Check(testkit.Rows())
 }
+
+func TestOptimizerCostFactorHints(t *testing.T) {
+	// This test covers a subset of the cost factorst - using hints to increase the cost factor
+	// of a specific plan type. The test is not exhaustive and does not cover all cost factors.
+	store := testkit.CreateMockStore(t)
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int, b int, c int, primary key (a), key(b))")
+	// Insert some data
+	tk.MustExec("insert into t values (1,1,1),(2,2,2),(3,3,3),(4,4,4),(5,5,5)")
+	// Analyze table to update statistics
+	tk.MustExec("analyze table t")
+
+	// Test tableFullScan cost factor increase via hint
+	// Set index scan cost factor variable to isolate testing to TableFullScan
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=100")
+	rs := tk.MustQuery("explain format=verbose select * from t").Rows()
+	planCost1, err1 := strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err1)
+	rs = tk.MustQuery("explain format=verbose select /*+ SET_VAR(tidb_opt_table_full_scan_cost_factor=2) */ * from t").Rows()
+	planCost2, err2 := strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err2)
+	// 1st query should be cheaper than 2nd query
+	require.Less(t, planCost1, planCost2)
+	// Reset to index scan to default
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=1")
+
+	// Test tableReader cost factor increase via hint
+	// Set index scan cost factor variable to isolate testing to TableReader
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=100")
+	rs = tk.MustQuery("explain format=verbose select * from t").Rows()
+	planCost1, err1 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err1)
+	rs = tk.MustQuery("explain format=verbose select /*+ SET_VAR(tidb_opt_table_reader_cost_factor=2) */ * from t").Rows()
+	planCost2, err2 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err2)
+	// 1st query should be cheaper than 2nd query
+	require.Less(t, planCost1, planCost2)
+	// Reset to index scan variable to default
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=1")
+
+	// Test tableRangeScan cost factor increase
+	// Set index scan and table full scan cost factor variables to isolate testing to TableRangeScan
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=100")
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=100")
+	rs = tk.MustQuery("explain format=verbose select * from t where a > 3").Rows()
+	planCost1, err1 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err1)
+	rs = tk.MustQuery("explain format=verbose select /*+ SET_VAR(tidb_opt_table_range_scan_cost_factor=2) */ * from t where a > 3").Rows()
+	planCost2, err2 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err2)
+	// 1st query should be cheaper than 2nd query
+	require.Less(t, planCost1, planCost2)
+	// Reset to index and table full scan variables to default
+	tk.MustExec("set @@session.tidb_opt_index_scan_cost_factor=1")
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=1")
+
+	// Test IndexScan cost factor increase
+	// Increase table scan cost factor to isolate testing to IndexScan
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=100")
+	rs = tk.MustQuery("explain format=verbose select b from t where b > 3").Rows()
+	planCost1, err1 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err1)
+	rs = tk.MustQuery("explain format=verbose select /*+ SET_VAR(tidb_opt_index_scan_cost_factor=2) */ b from t where b > 3").Rows()
+	planCost2, err2 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err2)
+	// 1st query should be cheaper than 2nd query
+	require.Less(t, planCost1, planCost2)
+	// Reset table full scan variable to default
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=1")
+
+	// Test IndexReadercost factor increase
+	// Increase table scan cost factor variable to isolate testing to IndexReader
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=100")
+	rs = tk.MustQuery("explain format=verbose select b from t where b > 3").Rows()
+	planCost1, err1 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err1)
+	rs = tk.MustQuery("explain format=verbose select  /*+ SET_VAR(tidb_opt_index_reader_cost_factor=2) */ b from t where b > 3").Rows()
+	planCost2, err2 = strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err2)
+	// 1st query should be cheaper than 2nd query
+	require.Less(t, planCost1, planCost2)
+	// Reset table scan cost factor variable to default
+	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=1")
+}

pkg/planner/core/plan_cost_ver2_test.go

@@ -673,7 +673,19 @@ func TestTiFlashCostFactors(t *testing.T) {
 	require.Nil(t, err3)
 	// 3rd query should be cheaper than 1st query
 	require.Less(t, planCost3, planCost1)
-	// Reset to default
+
+	// Reset TiFlash cost factor to default
 	tk.MustExec("set @@session.tidb_opt_table_tiflash_scan_cost_factor=1")
+
+	// Test TiFlash cost factor increase via hint
+	rs = tk.MustQuery("explain format=verbose select /*+ SET_VAR(tidb_opt_table_tiflash_scan_cost_factor=2) */ * from t").Rows()
+	planCost4, err4 := strconv.ParseFloat(rs[0][2].(string), 64)
+	require.Nil(t, err4)
+	// 1st query should be cheaper than 4th query
+	require.Less(t, planCost1, planCost4)
+
+	// Reset table scan cost factor to default
 	tk.MustExec("set @@session.tidb_opt_table_full_scan_cost_factor=1")
+	// Reset TiFlash cop to default
+	tk.MustExec("set @@session.tidb_allow_tiflash_cop=OFF")
 }

pkg/sessionctx/variable/setvar_affect.go

@@ -54,6 +54,23 @@ var isHintUpdatableVerified = map[string]struct{}{
 	"tidb_opt_concurrency_factor":                     {},
 	"tidb_opt_force_inline_cte":                       {},
 	"tidb_opt_use_invisible_indexes":                  {},
+	"tidb_opt_hash_agg_cost_factor":                   {},
+	"tidb_opt_hash_join_cost_factor":                  {},
+	"tidb_opt_index_join_cost_factor":                 {},
+	"tidb_opt_index_lookup_cost_factor":               {},
+	"tidb_opt_index_merge_cost_factor":                {},
+	"tidb_opt_index_reader_cost_factor":               {},
+	"tidb_opt_index_scan_cost_factor":                 {},
+	"tidb_opt_limit_cost_factor":                      {},
+	"tidb_opt_merge_join_cost_factor":                 {},
+	"tidb_opt_sort_cost_factor":                       {},
+	"tidb_opt_stream_agg_cost_factor":                 {},
+	"tidb_opt_table_full_scan_cost_factor":            {},
+	"tidb_opt_table_range_scan_cost_factor":           {},
+	"tidb_opt_table_reader_cost_factor":               {},
+	"tidb_opt_table_rowid_scan_cost_factor":           {},
+	"tidb_opt_table_tiflash_scan_cost_factor":         {},
+	"tidb_opt_topn_cost_factor":                       {},
 	"tidb_index_join_batch_size":                      {},
 	"tidb_index_lookup_size":                          {},
 	"tidb_index_serial_scan_concurrency":              {},