kv: add more tracing on the commit path

References #148523

Epic: none

Release note: None

Author: arulajmani

pkg/kv/kvclient/kvcoord/dist_sender.go

@@ -1472,6 +1472,7 @@ func (ds *DistSender) divideAndSendParallelCommit(
 	}
 	if swapIdx == -1 {
 		// No pre-commit QueryIntents. Nothing to split.
+		log.VEvent(ctx, 3, "no pre-commit QueryIntents found, sending batch as-is")
 		return ds.divideAndSendBatchToRanges(ctx, ba, rs, isReverse, true /* withCommit */, batchIdx)
 	}
 
@@ -1504,6 +1505,7 @@ func (ds *DistSender) divideAndSendParallelCommit(
 	qiResponseCh := make(chan response, 1)
 
 	sendPreCommit := func(ctx context.Context) {
+		log.VEvent(ctx, 3, "sending split out pre-commit QueryIntent batch")
 		// Map response index to the original un-swapped batch index.
 		// Remember that we moved the last QueryIntent in this batch
 		// from swapIdx to the end.
@@ -1562,7 +1564,9 @@ func (ds *DistSender) divideAndSendParallelCommit(
 
 	// Wait for the QueryIntent-only batch to complete and stitch
 	// the responses together.
+	log.VEvent(ctx, 3, "waiting for pre-commit QueryIntent batch response")
 	qiReply := <-qiResponseCh
+	log.VEventf(ctx, 3, "received pre-commit QueryIntent batch response")
 
 	// Handle error conditions.
 	if pErr != nil {

pkg/kv/kvclient/kvcoord/txn_interceptor_committer.go

@@ -195,6 +195,7 @@ func (tc *txnCommitter) SendLocked(
 		// so interceptors above the txnCommitter in the stack don't need to be
 		// made aware that the record is staging.
 		pErr = maybeRemoveStagingStatusInErr(pErr)
+		log.VEventf(ctx, 2, "batch with EndTxn(commit=true) failed: %v", pErr)
 		return nil, pErr
 	}
 
@@ -216,6 +217,7 @@ func (tc *txnCommitter) SendLocked(
 		// the EndTxn request, either because canCommitInParallel returned false
 		// or because there were no unproven in-flight writes (see txnPipeliner)
 		// and there were no writes in the batch request.
+		log.VEventf(ctx, 2, "parallel commit attempt for transaction %s resulted in explicit commit", br.Txn)
 		return br, nil
 	default:
 		return nil, kvpb.NewErrorf("unexpected response status without error: %v", br.Txn)
@@ -296,6 +298,8 @@ func (tc *txnCommitter) validateEndTxnBatch(ba *kvpb.BatchRequest) error {
 func (tc *txnCommitter) sendLockedWithElidedEndTxn(
 	ctx context.Context, ba *kvpb.BatchRequest, et *kvpb.EndTxnRequest,
 ) (br *kvpb.BatchResponse, pErr *kvpb.Error) {
+	log.VEventf(ctx, 2, "eliding EndTxn request for read-only, non-locking transaction")
+
 	// Send the batch without its final request, which we know to be the EndTxn
 	// request that we're eliding. If this would result in us sending an empty
 	// batch, mock out a reply instead of sending anything.