sql: remove no longer needed tricky login in physical planning

TODO: need to make sure that the same NodeID is resolved to the same SQL
instance in the instance resolver.

This commit removes logic that was introduced in
9e4364a for physical planning in
multi-tenant environment that made it so that whenever two consecutive
spans to be partitioned happened to have the same "safe split key", they
would end up on the same pod. This was needed in order to make sure that
spans corresponding to different column families within a single SQL row
would end up on the same SQL pod (otherwise, we'd get errors or
incorrect results due to partial SQL rows processed by different pods).
I believe this logic was needed only initially because we were using
round-robin strategy for assigning pods to spans. That logic, however,
was removed in bdda6a0, so I believe it
can be safely removed.

This removal makes sense conceptually too.

Release note: None

pkg/sql/distsql_physical_planner.go

@@ -1392,12 +1392,12 @@ func (dsp *DistSQLPlanner) partitionSpan(
 	nodeMap map[base.SQLInstanceID]int,
 	getSQLInstanceIDForKVNodeID func(roachpb.NodeID) (base.SQLInstanceID, SpanPartitionReason),
 	ignoreMisplannedRanges *bool,
-) (_ []SpanPartition, lastPartitionIdx int, _ error) {
+) ([]SpanPartition, error) {
 	it := planCtx.spanIter
 	// rSpan is the span we are currently partitioning.
 	rSpan, err := keys.SpanAddr(span)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
 	var lastSQLInstanceID base.SQLInstanceID
@@ -1411,11 +1411,11 @@ func (dsp *DistSQLPlanner) partitionSpan(
 	// these individual ranges.
 	for it.Seek(ctx, span, kvcoord.Ascending); ; it.Next(ctx) {
 		if !it.Valid() {
-			return nil, 0, it.Error()
+			return nil, it.Error()
 		}
 		replDesc, ignore, err := it.ReplicaInfo(ctx)
 		if err != nil {
-			return nil, 0, err
+			return nil, err
 		}
 		*ignoreMisplannedRanges = *ignoreMisplannedRanges || ignore
 		desc := it.Desc()
@@ -1441,7 +1441,6 @@ func (dsp *DistSQLPlanner) partitionSpan(
 			nodeMap[sqlInstanceID] = partitionIdx
 		}
 		partition := &partitions[partitionIdx]
-		lastPartitionIdx = partitionIdx
 
 		if len(span.EndKey) == 0 {
 			// If we see a span to partition that has no end key, it means that
@@ -1485,7 +1484,7 @@ func (dsp *DistSQLPlanner) partitionSpan(
 		lastKey = endKey
 		lastSQLInstanceID = sqlInstanceID
 	}
-	return partitions, lastPartitionIdx, nil
+	return partitions, nil
 }
 
 // deprecatedPartitionSpansSystem finds node owners for ranges touching the given spans
@@ -1499,7 +1498,7 @@ func (dsp *DistSQLPlanner) deprecatedPartitionSpansSystem(
 	}
 	for _, span := range spans {
 		var err error
-		partitions, _, err = dsp.partitionSpan(
+		partitions, err = dsp.partitionSpan(
 			ctx, planCtx, span, partitions, nodeMap, resolver, &ignoreMisplannedRanges,
 		)
 		if err != nil {
@@ -1523,24 +1522,8 @@ func (dsp *DistSQLPlanner) partitionSpans(
 		return nil, false, err
 	}
 	nodeMap := make(map[base.SQLInstanceID]int)
-	var lastKey roachpb.Key
-	var lastPartitionIdx int
 	for _, span := range spans {
-		// Rows with column families may have been split into different spans.
-		// These spans should be assigned the same pod so that the pod can
-		// stitch together the rows correctly. Split rows are in adjacent spans.
-		if safeKey, err := keys.EnsureSafeSplitKey(span.Key); err == nil && len(safeKey) > 0 {
-			if safeKey.Equal(lastKey) {
-				if log.V(1) {
-					log.Infof(ctx, "partitioning span %s", span)
-				}
-				partition := &partitions[lastPartitionIdx]
-				partition.Spans = append(partition.Spans, span)
-				continue
-			}
-			lastKey = safeKey
-		}
-		partitions, lastPartitionIdx, err = dsp.partitionSpan(
+		partitions, err = dsp.partitionSpan(
 			ctx, planCtx, span, partitions, nodeMap, resolver, &ignoreMisplannedRanges,
 		)
 		if err != nil {