Queries from search module are running for hours, slowing down the server, then killing MySQL

Hi,

I have an major problem with one of my Drupal sites which seems to be related to the Search module; it generates queries which are running for hours, first slowing down the server (AMD Opteron, Dual Core, 2 GB RAM), then killing MySQL completely. To prevent this, I have to restart mysql on a regular basis every few hours.

Symptoms:

Queries from mytop, appearing multiple times, until max_connections is reached:

DELETE FROM search_index WHERE fromsid = 3 AND fromtype = 'node'

SELECT t.word AS realword, i.word FROM search_total t LEFT JOIN search_index i ON t.word = i.word WHERE i.word IS NULL

with times ranging from 6643 to 42541 (= time the command/thread is executing), meaning, the queries run for hours and don't go away.

If I limit max_connections in my.conf to a small number (e.g. 16) these queries from the Drupal database user exceed this limit pretty fast (resulting in Drupal outputting the "Unable to connect to database server" error due to "The MySQL error: Too many connections"; if I extend max_connections to a higher value (e.g. 250), Drupal spawns an increasing number of long-running thread (like those mentioned above) that use up all server resources, until mysqld dies.

Since the queries seem to be caused by the search module, I tried to start a full reindex. That caused no recognizable enhancement; also, I changed a few parameters in my.conf, but the default configuration seems quite stable, "tweaks" tend to worsen things. Now, I'm running out of ideas.

Any suggestions what these non-ending queries are, why they don't go away, and what I can do to prevent them to kill the server are greatly appreciated!

System configuration: Drupal 5.5, Debian "Etch", Kernel 2.6.18-4-686 (SMP), MySQL 5.0.32, PHP 5.2.0-8+etch7, Apache 2.2.3, running on an Dual-Core AMD Opteron 1212 HE, 2 GB of RAM.

Thanks & regards, -asb