First off, apols for the 'considered harmful' cliché. Description: http://mbr.org Forum posts: 8576, with 63015 comments 1. Some tracker module queries, particularly the one which shows 'all my posts' to individual users, stop functioning on large data sets. In this case, queries ran for >600s 2. An INSERT/UPDATE on {comments} while those queries are trying to complete will be stalled, waiting for a full-table lock (MySQL + MyISAM). 3. While there is an INSERT/UPDATE waiting to execute, *all* other SELECTS on the same table are frozen and marked as 'Locked' in MySQL's process list until 1) and 2) are complete. Add 100 logged-in users, simmer for about 3 minutes -> MySQL server drops dead with 'Too many connections' (whether using mysql_pconnect() or not). Workaround: under *no* circumstances enable tracker.module on a heavily-used site which gives posting rights to visitors. There is, of course, a fix out there waiting to be written in either the query or the schema, but while I'm OK with adding indexes to tables, multi-table indexing is outside my comfort zone. [cross-posted to tracker: http://drupal.org/node/39351 ] The *good* news: disabling the tracker has reverted server load back down to 0.1 - 0.3 (from >30.00) and MBR is once again serving about 60,000 pages per day without complaint. Serious request for Infrastructure people: this sort of thing doesn't affect many of us, but it kills us when bad things happen. I'm not the first person to ask --- can we please have a "Scaling / Large site issues" forum on Drupal.org to collect war stories? jh