# Issue #60357: Require an ability to externally influence the optimizer cost model ## Metadata - Issue: https://github.com/pingcap/tidb/issues/60357 - Status: closed - Type: type/enhancement - Created At: 2025-04-02T00:50:13Z - Closed At: 2025-04-10T21:56:34Z - Labels: affects-8.5, report/customer, sig/planner, type/enhancement ## Customer-Facing Phenomenon - The TiDB optimizer would benefit from having an ability to influence the optimizer's cost of each physical operator in a query plan. This could be used externally to influence query plans (by customers/users and also TiDB engineers), and could be used by TiDB engineers to test and adjust the optimizer's cost model. ## Linked PRs - Fix PR #60333: planner: add optimizer cost factors URL: https://github.com/pingcap/tidb/pull/60333 State: closed Merged At: 2025-04-10T21:56:33Z Changed Files Count: 9 Main Modules: tests/integrationtest, pkg/session, pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2.go - pkg/planner/core/plan_cost_ver2_test.go - pkg/sessionctx/vardef/tidb_vars.go - pkg/sessionctx/variable/session.go - pkg/sessionctx/variable/sysvar.go - tests/integrationtest/r/executor/explain.result - tests/integrationtest/r/planner/core/cbo.result - tests/integrationtest/r/planner/core/plan_cache.result - tests/integrationtest/r/planner/core/plan_cost_ver2.result PR Summary: What problem does this PR solve? Problem Summary: What changed and how does it work? Add a global variable "cost factor" to the more common optimizer physical operators. This allows an ability to externally control the optimizer's plan choice(s) - by either increasing the cost factor for one operation (to discourage that plan choice), or decreasing the cost factor of an operation (to encourage that plan choice). - Fix PR #60512: planner: add optimizer cost factor tests URL: https://github.com/pingcap/tidb/pull/60512 State: closed Merged At: 2025-04-14T03:55:06Z Changed Files Count: 1 Main Modules: pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2_test.go PR Summary: What problem does this PR solve? Problem Summary: What changed and how does it work? Add testcases for recent optimizer cost factors. - Fix PR #60558: planner: add hint support for optimizer cost factors URL: https://github.com/pingcap/tidb/pull/60558 State: closed Merged At: 2025-04-16T04:27:58Z Changed Files Count: 4 Main Modules: pkg/planner/core, pkg/session Sample Changed Files: - pkg/planner/core/casetest/hint/BUILD.bazel - pkg/planner/core/casetest/hint/hint_test.go - pkg/planner/core/plan_cost_ver2_test.go - pkg/sessionctx/variable/setvar_affect.go PR Summary: What problem does this PR solve? Problem Summary: What changed and how does it work? - Fix PR #61765: planner: add optimizer cost factors (#60333) URL: https://github.com/pingcap/tidb/pull/61765 State: closed Merged At: 2025-06-25T15:23:21Z Changed Files Count: 9 Main Modules: tests/integrationtest, pkg/session, pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2.go - pkg/planner/core/plan_cost_ver2_test.go - pkg/sessionctx/variable/session.go - pkg/sessionctx/variable/sysvar.go - pkg/sessionctx/variable/tidb_vars.go - tests/integrationtest/r/executor/explain.result - tests/integrationtest/r/planner/core/cbo.result - tests/integrationtest/r/planner/core/plan_cache.result - tests/integrationtest/r/planner/core/plan_cost_ver2.result PR Summary: This is an automated cherry-pick of #60333 What problem does this PR solve? Problem Summary: What changed and how does it work? Add a global variable "cost factor" to the more common optimizer physical operators. This allows an ability to externally control the optimizer's plan choice(s) - by either increasing the cost factor for one operation (to discourage that plan choice), or decreasing the cost factor of an operation (to encourage that plan choice). - Fix PR #61903: planner: add optimizer cost factor tests (#60512) URL: https://github.com/pingcap/tidb/pull/61903 State: closed Merged At: 2025-07-02T19:48:27Z Changed Files Count: 1 Main Modules: pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2_test.go PR Summary: This is an automated cherry-pick of #60512 What problem does this PR solve? Problem Summary: What changed and how does it work? Add testcases for recent optimizer cost factors. - Fix PR #61904: planner: add hint support for optimizer cost factors (#60558) URL: https://github.com/pingcap/tidb/pull/61904 State: closed Merged At: 2025-07-07T13:43:33Z Changed Files Count: 4 Main Modules: pkg/planner/core, pkg/session Sample Changed Files: - pkg/planner/core/casetest/hint/BUILD.bazel - pkg/planner/core/casetest/hint/hint_test.go - pkg/planner/core/plan_cost_ver2_test.go - pkg/sessionctx/variable/setvar_affect.go PR Summary: This is an automated cherry-pick of #60558 What problem does this PR solve? Problem Summary: What changed and how does it work? - Fix PR #64553: planner: add optimizer cost factors URL: https://github.com/pingcap/tidb/pull/64553 State: closed Merged At: not merged Changed Files Count: 4 Main Modules: pkg/session, pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2.go - pkg/sessionctx/variable/session.go - pkg/sessionctx/variable/sysvar.go - pkg/sessionctx/variable/tidb_vars.go PR Summary: What problem does this PR solve? Problem Summary: What changed and how does it work? - Related PR #64564: planner: add optimizer cost factors | tidb-test=release-8.5-20250114-v8.5.0 URL: https://github.com/pingcap/tidb/pull/64564 State: closed Merged At: 2025-11-19T15:38:41Z Changed Files Count: 9 Main Modules: tests/integrationtest, pkg/session, pkg/planner/core Sample Changed Files: - pkg/planner/core/plan_cost_ver2.go - pkg/planner/core/plan_cost_ver2_test.go - pkg/sessionctx/variable/session.go - pkg/sessionctx/variable/sysvar.go - pkg/sessionctx/variable/tidb_vars.go - tests/integrationtest/r/executor/explain.result - tests/integrationtest/r/planner/core/cbo.result - tests/integrationtest/r/planner/core/plan_cache.result - tests/integrationtest/r/planner/core/plan_cost_ver2.result PR Summary: What problem does this PR solve? Problem Summary: cherry pick to v8.5.0 for hotfix What changed and how does it work? ## Notes - At least one merged PR was found. The merge timestamp above can be used as the fix landing time in the main branch.