After upgrading to Confluence version 5.1.5, the Macro Migration Service configuration in BANDANA table is set to true.

Configuration can be found by using this query:

SELECT * FROM bandana WHERE BANDANACONTEXT = 'com.atlassian.confluence.content.render.xhtml.migration.macro.MacroMigrationService' AND BANDANAKEY = 'migration.required';

This causes Confluence instance with lot of pages and users suddenly performing great number of editing operations in the database and may cause an outage.