diff --git a/src/t_stream.c b/src/t_stream.c
index c51dc94c..9835573d 100644
--- a/src/t_stream.c
+++ b/src/t_stream.c
@@ -149,6 +149,17 @@ void streamDecodeID(void *buf, streamID *id) {
     id->seq = ntohu64(e[1]);
 }
 
+/* Compare two stream IDs. Return -1 if a < b, 0 if a == b, 1 if a > b. */
+int streamCompareID(streamID *a, streamID *b) {
+    if (a->ms > b->ms) return 1;
+    else if (a->ms < b->ms) return -1;
+    /* The ms part is the same. Check the sequence part. */
+    else if (a->seq > b->seq) return 1;
+    else if (a->seq < b->seq) return -1;
+    /* Everything is the same: IDs are equal. */
+    return 0;
+}
+
 /* Adds a new item into the stream 's' having the specified number of
  * field-value pairs as specified in 'numfields' and stored into 'argv'.
  * Returns the new entry ID populating the 'added_id' structure.
@@ -164,9 +175,7 @@ void streamDecodeID(void *buf, streamID *id) {
 int streamAppendItem(stream *s, robj **argv, int numfields, streamID *added_id, streamID *use_id) {
     /* If an ID was given, check that it's greater than the last entry ID
      * or return an error. */
-    if (use_id && (use_id->ms < s->last_id.ms ||
-                   (use_id->ms == s->last_id.ms &&
-                    use_id->seq <= s->last_id.seq))) return C_ERR;
+    if (use_id && streamCompareID(use_id,&s->last_id) <= 0) return C_ERR;
 
     /* Add the new entry. */
     raxIterator ri;
@@ -679,8 +688,21 @@ size_t streamReplyWithRange(client *c, stream *s, streamID *start, streamID *end
     int64_t numfields;
     streamID id;
 
+    /* If a group was passed, as an optimization we check if the range
+     * specified is about messages that were never delivered. This is true if
+     * the 'start' range is greater than the current last_id in the stream.
+     * In that case, there is no need to check if the messages may already
+     * have another owner before delivering the message. This speeds up
+     * the processing significantly. */
+    int newmessages = group != NULL &&
+                      streamCompareID(start,&group->last_id) > 0;
+
     streamIteratorStart(&si,s,start,end,rev);
     while(streamIteratorGetID(&si,&id,&numfields)) {
+        /* Update the group last_id if needed. */
+        if (group && streamCompareID(&id,&group->last_id) > 0)
+            group->last_id = id;
+
         /* Emit a two elements array for each item. The first is
          * the ID, the second is an array of field-value pairs. */
         sds replyid = sdscatfmt(sdsempty(),"+%U-%U\r\n",id.ms,id.seq);
@@ -1134,8 +1156,15 @@ void streamNotAckedFree(streamNotAcked *na) {
     zfree(na);
 }
 
+/* Free a consumer and associated data structures. Note that this function
+ * will not reassign the pending messages associated with this consumer
+ * nor will delete them from the stream, so when this function is called
+ * to delete a consumer, and not when the whole stream is destroyed, the caller
+ * should do some work before. */
 void streamConsumerFree(streamConsumer *sc) {
-    zfree(sc->name);
+    raxFree(sc->pel); /* No value free callback: the PEL entries are shared
+                         between the consumer and the main stream PEL. */
+    sdsfree(sc->name);
     zfree(sc);
 }