Well, I was going to wave you at the standard Jira knowledge base article on this, but Atlassian seem to have deleted it.
Anyway, this is often down to slowness, so here's a quick list of things to look at initially:
If you were on a Windows box then virus scanners are notorious for breaking services like this
What version of Java are you running? Is it a 1.7 JDK?
What is the server's hardware like? Lots of memory etc?
What are your memory settings for the JVM?
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