Slow response when updating a biblio node

Problem/Motivation

I manage a site with (currently) about 4600 biblio entries and something like 21000 contributors. When you edit a biblio node and then save, even if no changes were made, it will hang for upwards of 45 seconds each time. If several people do it at once it will make the site unresponsive for several minutes at least.

Here's the MySQL slow query log entry:

# Query_time: 85.980024 Lock_time: 0.000044 Rows_sent: 0 Rows_examined: 117888631
use msrc_drupal;
SET timestamp=1316028478;
DELETE FROM biblio_contributor_data
WHERE (cid NOT IN (SELECT DISTINCT bc.cid AS cid
FROM
biblio_contributor bc));

Proposed resolution

I tracked the problem down to the delete_orphan_authors() function in biblio.contributors.inc . This runs every time you save a node, called by biblio_update_contributors(). Can we change this to run either only when requested or by cron perhaps once a day, or optimize the query so it doesn't hang on large databases? I currently commented out this call in the update function to make the site usable again when editing entries (currently we create a node, then go in and edit it to attach a PDF).