Recently after upgrading a project from Sitecore 7.2 rev.140314 (Update 1), the application start up time increased from about 30 seconds to load the first page to over 3 minutes. The only change that was made was following the upgrade steps as described on the SDN.
After some help diagnosing from Sitecore support, they suggested adding a hidden setting to our configuration to see if it resolved the issue. This was the suggested setting to add:
The impact of adding this setting is as expected, it disables the cloning functionality (you can read about Sitecore's cloning functionality in Section 4.6 of the Content Author's Cookbook). The other impact found was that the site start up time had returned to its previous speed and resolved the issue.
The issue has been raised as a bug with the software and can be tracked using the reference number 436659 (for information on reference numbers you can read the KB article).
The release notes of Sitecore 7.2 Update-5 indicate that this issue has been resolved.
The performance of the get item operation for both regular and clone items has been increased by introducing a separate shared field called ‘__Source Item’. This now allows you to keep a reference to original item. (436659)