planner: disable tiflash late materialization when fast scan is enable (#42683)

close #40601

Author: Lloyd-Pottiger

planner/core/optimizer.go

@@ -555,9 +555,13 @@ func prunePhysicalColumnsInternal(sctx sessionctx.Context, plan PhysicalPlan) er
 //   - Filter conditions that apply to the same column are either pushed down or not pushed down at all.
 func tryEnableLateMaterialization(sctx sessionctx.Context, plan PhysicalPlan) {
 	// check if EnableLateMaterialization is set
-	if sctx.GetSessionVars().EnableLateMaterialization {
+	if sctx.GetSessionVars().EnableLateMaterialization && !sctx.GetSessionVars().TiFlashFastScan {
 		predicatePushDownToTableScan(sctx, plan)
 	}
+	if sctx.GetSessionVars().EnableLateMaterialization && sctx.GetSessionVars().TiFlashFastScan {
+		sc := sctx.GetSessionVars().StmtCtx
+		sc.AppendWarning(errors.New("FastScan is not compatible with late materialization, late materialization is disabled"))
+	}
 }
 
 /*

planner/core/tiflash_selection_late_materialization.go

@@ -178,6 +178,9 @@ func withHeavyCostFunctionForTiFlashPrefetch(cond expression.Expression) bool {
 			return true
 		case ast.StrToDate, ast.SubDate, ast.SubTime, ast.TimeLiteral, ast.TimeFormat, ast.TimeToSec, ast.TimeDiff, ast.TimestampDiff:
 			return true
+		// regexp functions
+		case ast.Regexp, ast.RegexpLike, ast.RegexpReplace, ast.RegexpSubstr, ast.RegexpInStr:
+			return true
 			// TODO: add more heavy cost functions
 		}
 	}
@@ -203,7 +206,7 @@ func removeSpecificExprsFromSelection(physicalSelection *PhysicalSelection, expr
 // @param: physicalTableScan: the PhysicalTableScan to be pushed down to
 func predicatePushDownToTableScanImpl(sctx sessionctx.Context, physicalSelection *PhysicalSelection, physicalTableScan *PhysicalTableScan) {
 	// When the table is small, there is no need to push down the conditions.
-	if physicalTableScan.tblColHists.RealtimeCount <= tiflashDataPackSize {
+	if physicalTableScan.tblColHists.RealtimeCount <= tiflashDataPackSize || physicalTableScan.KeepOrder {
 		return
 	}
 	conds := physicalSelection.Conditions