fix: Calling Discard only adds to txn_discards metric, not txn_aborts. (

#7365)

This PR is a follow-up to #7339 to update the way
dgraph_txn_discards_total and dgraph_txn_aborts_total are
tracked. When the client calls Discard, only the
dgraph_txn_discards_total metric is incremented, not
dgraph_txn_aborts_total. This makes it easy to see:

1. If the client is calling Discard
2. If the server is aborting transactions (e.g., because of
   transaction conflicts)

Additional changes:

* Update metrics description text

worker/mutation.go

@@ -767,9 +767,12 @@ func typeSanityCheck(t *pb.TypeUpdate) error {
 func CommitOverNetwork(ctx context.Context, tc *api.TxnContext) (uint64, error) {
 	ctx, span := otrace.StartSpan(ctx, "worker.CommitOverNetwork")
 	defer span.End()
+
+	clientDiscard := false
 	if tc.Aborted {
 		// The client called Discard
 		ostats.Record(ctx, x.TxnDiscards.M(1))
+		clientDiscard = true
 	}
 
 	pl := groups().Leader(0)
@@ -789,8 +792,10 @@ func CommitOverNetwork(ctx context.Context, tc *api.TxnContext) (uint64, error)
 	span.Annotate(attributes, "")
 
 	if tctx.Aborted || tctx.CommitTs == 0 {
-		// The server aborted the txn (not the client)
-		ostats.Record(ctx, x.TxnAborts.M(1))
+		if !clientDiscard {
+			// The server aborted the txn (not the client)
+			ostats.Record(ctx, x.TxnAborts.M(1))
+		}
 		return 0, dgo.ErrAborted
 	}
 	ostats.Record(ctx, x.TxnCommits.M(1))

x/metrics.go

@@ -102,12 +102,12 @@ var (
 	// TxnCommits records count of committed transactions.
 	TxnCommits = stats.Int64("txn_commits_total",
 		"Number of transaction commits", stats.UnitDimensionless)
-	// TxnDiscards records count of discarded transactions.
+	// TxnDiscards records count of discarded transactions by the client.
 	TxnDiscards = stats.Int64("txn_discards_total",
-		"Number of transaction discards", stats.UnitDimensionless)
-	// TxnAborts records count of aborted transactions.
+		"Number of transaction discards by the client", stats.UnitDimensionless)
+	// TxnAborts records count of aborted transactions by the server.
 	TxnAborts = stats.Int64("txn_aborts_total",
-		"Number of transaction aborts", stats.UnitDimensionless)
+		"Number of transaction aborts by the server", stats.UnitDimensionless)
 	// PBlockHitRatio records the hit ratio of posting store block cache.
 	PBlockHitRatio = stats.Float64("hit_ratio_postings_block",
 		"Hit ratio of p store block cache", stats.UnitDimensionless)