planner: refactor some code related to IndexMerge and MVIndex (#40800)

ref #40191

planner/core/indexmerge_path.go

@@ -15,7 +15,6 @@
 package core
 
 import (
- "fmt"
  "math"
  "strings"
 
@@ -37,6 +36,16 @@ import (
 
 // generateIndexMergePath generates IndexMerge AccessPaths on this DataSource.
 func (ds *DataSource) generateIndexMergePath() error {
+ var warningMsg string
+ stmtCtx := ds.ctx.GetSessionVars().StmtCtx
+ defer func() {
+ if len(ds.indexMergeHints) > 0 && warningMsg != "" {
+ ds.indexMergeHints = nil
+ stmtCtx.AppendWarning(errors.Errorf(warningMsg))
+ logutil.BgLogger().Debug(warningMsg)
+ }
+ }()
+
  // Consider the IndexMergePath. Now, we just generate `IndexMergePath` in DNF case.
  // Use allConds instread of pushedDownConds,
  // because we want to use IndexMerge even if some expr cannot be pushed to TiKV.
@@ -46,11 +55,26 @@ func (ds *DataSource) generateIndexMergePath() error {
  indexMergeConds = append(indexMergeConds, expression.PushDownNot(ds.ctx, expr))
  }
 
- stmtCtx := ds.ctx.GetSessionVars().StmtCtx
  isPossibleIdxMerge := len(indexMergeConds) > 0 && // have corresponding access conditions, and
  (len(ds.possibleAccessPaths) > 1 || // (have multiple index paths, or
  (len(ds.possibleAccessPaths) == 1 && isMVIndexPath(ds.possibleAccessPaths[0]))) // have a MVIndex)
+
+ if !isPossibleIdxMerge {
+ warningMsg = "IndexMerge is inapplicable or disabled. No available filter or available index."
+ return nil
+ }
+
  sessionAndStmtPermission := (ds.ctx.GetSessionVars().GetEnableIndexMerge() || len(ds.indexMergeHints) > 0) && !stmtCtx.NoIndexMergeHint
+ if !sessionAndStmtPermission {
+ warningMsg = "IndexMerge is inapplicable or disabled. Got no_index_merge hint or tidb_enable_index_merge is off."
+ return nil
+ }
+
+ if ds.tableInfo.TempTableType == model.TempTableLocal {
+ warningMsg = "IndexMerge is inapplicable or disabled. Cannot use IndexMerge on temporary table."
+ return nil
+ }
+
  // We current do not consider `IndexMergePath`:
  // 1. If there is an index path.
  // 2. TODO: If there exists exprs that cannot be pushed down. This is to avoid wrongly estRow of Selection added by rule_predicate_push_down.
@@ -87,26 +111,37 @@ func (ds *DataSource) generateIndexMergePath() error {
  }
  }
 
- if isPossibleIdxMerge && sessionAndStmtPermission && needConsiderIndexMerge && ds.tableInfo.TempTableType != model.TempTableLocal {
- err := ds.generateAndPruneIndexMergePath(indexMergeConds, ds.indexMergeHints != nil)
- if err != nil {
- return err
- }
- } else if len(ds.indexMergeHints) > 0 {
+ if !needConsiderIndexMerge {
+ warningMsg = "IndexMerge is inapplicable or disabled. "
+ return nil
+ }
+ regularPathCount := len(ds.possibleAccessPaths)
+ if err := ds.generateAndPruneIndexMergePath(indexMergeConds); err != nil {
+ return err
+ }
+
+ // If without hints, it means that `enableIndexMerge` is true
+ if len(ds.indexMergeHints) == 0 {
+ return nil
+ }
+ // If len(indexMergeHints) > 0, then add warnings if index-merge hints cannot work.
+ if regularPathCount == len(ds.possibleAccessPaths) {
  ds.indexMergeHints = nil
- var msg string
- if !isPossibleIdxMerge {
- msg = "No available filter or available index."
- } else if !sessionAndStmtPermission {
- msg = "Got no_index_merge hint or tidb_enable_index_merge is off."
- } else if ds.tableInfo.TempTableType == model.TempTableLocal {
- msg = "Cannot use IndexMerge on temporary table."
- }
- msg = fmt.Sprintf("IndexMerge is inapplicable or disabled. %s", msg)
- stmtCtx.AppendWarning(errors.Errorf(msg))
- logutil.BgLogger().Debug(msg)
+ ds.ctx.GetSessionVars().StmtCtx.AppendWarning(errors.Errorf("IndexMerge is inapplicable"))
+ return nil
  }
 
+ // If len(indexMergeHints) > 0 and some index-merge paths were added, then prune all other non-index-merge paths.
+ ds.possibleAccessPaths = ds.possibleAccessPaths[regularPathCount:]
+ minRowCount := ds.possibleAccessPaths[0].CountAfterAccess
+ for _, path := range ds.possibleAccessPaths {
+ if minRowCount < path.CountAfterAccess {
+ minRowCount = path.CountAfterAccess
+ }
+ }
+ if ds.stats.RowCount > minRowCount {
+ ds.stats = ds.tableStats.ScaleByExpectCnt(minRowCount)
+ }
  return nil
 }
 
@@ -441,7 +476,7 @@ func (ds *DataSource) generateIndexMergeAndPaths(normalPathCnt int) *util.Access
  return indexMergePath
 }
 
-func (ds *DataSource) generateAndPruneIndexMergePath(indexMergeConds []expression.Expression, needPrune bool) error {
+func (ds *DataSource) generateAndPruneIndexMergePath(indexMergeConds []expression.Expression) error {
  regularPathCount := len(ds.possibleAccessPaths)
  // 1. Generate possible IndexMerge paths for `OR`.
  err := ds.generateIndexMergeOrPaths(indexMergeConds)
@@ -461,36 +496,6 @@ func (ds *DataSource) generateAndPruneIndexMergePath(indexMergeConds []expressio
  if mvIndexMergePath != nil {
  ds.possibleAccessPaths = append(ds.possibleAccessPaths, mvIndexMergePath...)
  }
-
- // 4. If needed, append a warning if no IndexMerge is generated.
-
- // If without hints, it means that `enableIndexMerge` is true
- if len(ds.indexMergeHints) == 0 {
- return nil
- }
- // With hints and without generated IndexMerge paths
- if regularPathCount == len(ds.possibleAccessPaths) {
- ds.indexMergeHints = nil
- ds.ctx.GetSessionVars().StmtCtx.AppendWarning(errors.Errorf("IndexMerge is inapplicable"))
- return nil
- }
-
- // 4. If needPrune is true, prune non-IndexMerge paths.
-
- // Do not need to consider the regular paths in find_best_task().
- // So we can use index merge's row count as DataSource's row count.
- if needPrune {
- ds.possibleAccessPaths = ds.possibleAccessPaths[regularPathCount:]
- minRowCount := ds.possibleAccessPaths[0].CountAfterAccess
- for _, path := range ds.possibleAccessPaths {
- if minRowCount < path.CountAfterAccess {
- minRowCount = path.CountAfterAccess
- }
- }
- if ds.stats.RowCount > minRowCount {
- ds.stats = ds.tableStats.ScaleByExpectCnt(minRowCount)
- }
- }
  return nil
 }