roachpb: update the explanation of the TxnCoordMeta.refresh_invalid f…

…ield

Release justification: only comments

Release note: None

pkg/roachpb/data.proto

@@ -635,11 +635,10 @@ message TxnCoordMeta {
   repeated Span refresh_reads = 4 [(gogoproto.nullable) = false];
   repeated Span refresh_writes = 5 [(gogoproto.nullable) = false];
   reserved 6;
-  // refresh_invalid indicates that spans were discarded or not collected
-  // (i.e. because of a dist SQL processor running a version before refreshing
-  // was introduced). This is false if all spans encountered during the
-  // transaction which need refreshing have been collected to the refresh_reads
-  // and refresh_writes span slices.
+  // refresh_invalid indicates that spans were discarded or not collected (i.e.
+  // because the memory budget for tracking reads was exceeded). This is false
+  // if all spans encountered during the transaction which need refreshing have
+  // been collected to the refresh_reads and refresh_writes span slices.
   bool refresh_invalid = 7;
   // in_flight_writes stores all writes that are in-flight and have not yet
   // been proven to have succeeded. Any client wishing to send a request that