There are some issues in using PG 7.4.x and max() on tables with large number of rows, and the CR was having issues with that at any time a CR item was created, therefore and based on previous Jeff's acs-objetcs upgrade, now the CR has a new upgrade for improve this (Galileo installation nowadays has more than 1 million of cr_items, and with this improvement the cr_item creation decreased from ~850ms to ~20ms).
Any large OpenACS site that heavily uses the CR, including those that use .LRN, should do the upgrade, which is located in oacs-5-2 branch, but can be performed in .LRN based on oacs-5-1 (since the upgrade is not dependent to the new stuff added to oacs-5-2), and if you upgrade separately, when you upgrade to oacs-5-2 manually avoid running that upgrade script again.
http://cvs.openacs.org/cvs/openacs-4/packages/acs-content-repository/sql/postgresql/upgrade/Attic/upgrade-5.2.0b2-5.2.0b3.sql?rev=1.1.2.1&only_with_tag=oacs-5-2&view=auto
This problem is not present in oracle.
