diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
index ca074da..fff1fdd 100644
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -6,6 +6,62 @@
  * This module is a pg_clog-like system that stores the commit timestamp
  * for each transaction.
  *
+ * When track_commit_timestamp is enabled, this module will keep track of
+ * commit timestamp for each transaction. It also provides API to for
+ * optionally storing nodeid (origin) of each transaction. The main purpose of
+ * this functionality is to help with conflict detection and resolution for
+ * replication systems.
+ *
+ * The following example shows how to use the API provided by this module, to
+ * handle UPDATE conflicts coming from replication stream:
+ * void
+ * update_tuple(Relation relation, HeapTuple remote_tuple,
+ *              TimestampTz remote_commit_ts, CommitTsNodeId remote_node_id)
+ * {
+ *     bool             exists;
+ *     HeapTupleData    local_tuple;
+ *
+ *     // Find existing tuple with same PK/unique index combination.
+ *     exists = find_local_tuple(relation, remote_tuple, &local_tuple);
+ *
+ *     // The tuple was found.
+ *     if (exists)
+ *     {
+ *         TransactionId    xmin;
+ *         TimestampTz      local_commit_ts;
+ *         CommitTsNodeId   local_node_id;
+ *
+ *         xmin = HeapTupleHeaderGetXmin(local_tuple.t_data);
+ *         TransactionIdGetCommitTsData(xmin, &local_commit_ts, &nodeid);
+ *
+ *         // New tuple is coming from different node than the locally saved
+ *         // tuple and the remote commit timestamp is older than local commit
+ *         // timestamp, this is UPDATE/UPDATE conflict (node being UPDATEd on
+ *         // different nodes at the same time.
+ *         if (remote_id != local_node_id && remote_commit_ts <= local_commit_ts)
+ *         {
+ *             if (remote_commit_ts < local_commit_ts)
+ *                 return; // Keep the local tuple.
+ *
+ *             // Handle the conflict in a consistent manner.
+ *         }
+ *         else
+ *         {
+ *             // The new tuple either comes from same node as old tuple and/or
+ *             // is has newer commit timestamp than the local tuple, apply the
+ *             // UPDATE.
+ *         }
+ *      }
+ *      else
+ *      {
+ *          // Tuple not found (possibly UPDATE/DELETE conflict), handle it
+ *          // in a consistent manner.
+ *      }
+ * }
+ *
+ * See default_node_id and CommitTsSetDefaultNodeId for explanation of how to
+ * set nodeid when applying transactions.
+ *
  * XLOG interactions: this module generates an XLOG record whenever a new
  * CommitTs page is initialized to zeroes.  Also, one XLOG record is
  * generated for setting of values when the caller requests it; this allows
@@ -49,6 +105,15 @@
  */
 
 /*
+ * CommitTimestampEntry
+ *
+ * Record containing information about the transaction commit timestamp and
+ * the nodeid.
+ *
+ * The nodeid provides IO efficient way for replication systems to store
+ * information about origin of the transaction. Currently the nodeid is opaque
+ * value meaning of which is defined by the replication system itself.
+ *
  * We need 8+4 bytes per xact.  Note that enlarging this struct might mean
  * the largest possible file name is more than 5 chars long; see
  * SlruScanDirectory.
@@ -93,6 +158,21 @@ CommitTimestampShared	*commitTsShared;
 /* GUC variable */
 bool	track_commit_timestamp;
 
+/*
+ * The default_node_id will be written to commit timestamp record for
+ * every transaction committed by the current backend.
+ *
+ * The idea behind having default_node_id is that replication system
+ * will have connection (backend running) for specific source of replicated
+ * data to which it assigned the nodeid for identification purposes.
+ *
+ * The default_node_id setting stays in effect for duration of a session
+ * (unless changed again), so the replication system does not have to set
+ * the nodeid individually for each transaction.
+ *
+ * The public access to the default_node_id is provided by
+ * CommitTsSetDefaultNodeId and CommitTsGetDefaultNodeId interfaces.
+ */
 static CommitTsNodeId default_node_id = InvalidCommitTsNodeId;
 
 static void SetXidCommitTsInPage(TransactionId xid, int nsubxids,
@@ -112,7 +192,7 @@ static void WriteSetTimestampXlogRec(TransactionId mainxid, int nsubxids,
 /*
  * CommitTsSetDefaultNodeId
  *
- * Set default nodeid for current backend.
+ * Set default nodeid for current session.
  */
 void
 CommitTsSetDefaultNodeId(CommitTsNodeId nodeid)
@@ -123,7 +203,7 @@ CommitTsSetDefaultNodeId(CommitTsNodeId nodeid)
 /*
  * CommitTsGetDefaultNodeId
  *
- * Set default nodeid for current backend.
+ * Get current default nodeid.
  */
 CommitTsNodeId
 CommitTsGetDefaultNodeId(void)