storage: add comment on readOnlyCmdMu

Release note: None
cockroachdb · Dec 14, 2018 · 2e3af6b · 2e3af6b
1 parent df26cf6
commit 2e3af6b
Showing 1 changed file with 6 additions and 0 deletions.
diff --git a/pkg/storage/replica.go b/pkg/storage/replica.go
@@ -307,6 +307,12 @@ type Replica struct {
 	// Held in read mode during read-only commands. Held in exclusive mode to
 	// prevent read-only commands from executing. Acquired before the embedded
 	// RWMutex.
+	//
+	// This mutex ensures proper interleaving of splits with concurrent reads.
+	// Splits register an MVCC write span latch, but reads at lower timestamps
+	// aren't held up by this latch, which could result in reads on the RHS
+	// executed through the LHS after this is valid. For more detail, see:
+	// https://github.com/cockroachdb/cockroach/issues/32583.
 	readOnlyCmdMu syncutil.RWMutex
 
 	// rangeStr is a string representation of a RangeDescriptor that can be