Index: modules/comment/comment.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/comment/comment.module,v
retrieving revision 1.498
diff -u -F^f -r1.498 comment.module
--- modules/comment/comment.module	21 Nov 2006 20:14:17 -0000	1.498
+++ modules/comment/comment.module	22 Nov 2006 18:17:31 -0000
@@ -172,13 +172,32 @@ function comment_block($op = 'list', $de
   }
 }
 
+/**
+ * Returns a formatted list of recent comments to be displayed in the comment block.
+ *
+ * @ingroup themeable
+ */
 function theme_comment_block() {
-  $result = db_query_range(db_rewrite_sql('SELECT c.nid, c.subject, c.cid, c.timestamp FROM {comments} c INNER JOIN {node} n ON n.nid = c.nid WHERE n.status = 1 AND c.status = %d ORDER BY c.timestamp DESC', 'c'), COMMENT_PUBLISHED, 0, 10);
-  $items = array();
-  while ($comment = db_fetch_object($result)) {
-    $items[] = l($comment->subject, 'node/'. $comment->nid, NULL, NULL, 'comment-'. $comment->cid) .'<br />'. t('@time ago', array('@time' => format_interval(time() - $comment->timestamp)));
+  // Select the 10 nodes (visible to the current user) with the most recent comments.  This is efficient due to the index on last_comment_timestamp.
+  $result = db_query_range(db_rewrite_sql("SELECT n.nid from {node_comment_statistics} n WHERE n.comment_count > 0 ORDER BY n.last_comment_timestamp DESC"), 0, 10);
+
+  $recent_nids = array();
+
+  while ($cnode = db_fetch_object($result)) {
+    $recent_nids[] = $cnode->nid;
+  }
+  if (count($recent_nids) > 0) {
+    // From among the comments on the 10 nodes selected in the first query, find the 10 most recent comments.
+    $result = db_query_range('SELECT c.nid, c.subject, c.cid, c.timestamp FROM {comments} c INNER JOIN {node} n ON n.nid = c.nid WHERE c.nid IN ('. implode(',', $recent_nids) .') AND n.status = 1 AND c.status = %d ORDER BY c.timestamp DESC', COMMENT_PUBLISHED, 0, 10);
+    $items = array();
+    while ($comment = db_fetch_object($result)) {
+      $items[] = l($comment->subject, 'node/'. $comment->nid, NULL, NULL, 'comment-'. $comment->cid) .'<br />'. t('@time ago', array('@time' => format_interval(time() - $comment->timestamp)));
+    }
+    return theme('item_list', $items);
+  }
+  else {
+    return '';
   }
-  return theme('item_list', $items);
 }
 
 /**