The schema service will hang there if the link to the schema in xml_catalog table is not accessible
When I upgraded the ESA metacat, i found that an issue that Tomcat couldn't start. It turns out that Metacat was trying to download a schema file from data.esa.org which hadn't been up yet during in the Metacat initialize method. So it was in a dead loop.
I have to change the schema from a http url to a file. Then it works. It is weird that it worked before the upgrade. I believe something is changed in tomcat 7 or openjdk 7. We should use some timeout mechanism to prevent this happening.