AD synchronisation. OutOfMemoryError: Java heap space

Hello.
Every time when Confluence Internal Directory synchronise with MS Active Directory we have this problems:
1. Any page loads for 3-4 minutes
2. Heap memory 1% free
3. Cpu loads for 70-80%
Finally, we have got "Synchronisation failed". And job scheduler doesn't works.
Logs:
Jan 31, 2014 2:54:12 PM com.sun.jersey.server.impl.application.WebApplicationImpl _initiate
INFO: Initiating Jersey application, version 'Jersey: 1.8-atlassian-11 03/22/2013 05:02 PM'
Exception in thread "scheduler_QuartzSchedulerThread" java.lang.OutOfMemoryError: Java heap space
Exception in thread "http-80-40" java.lang.NullPointerException
at java.util.concurrent.ConcurrentLinkedQueue.checkNotNull(Unknown Source)
at java.util.concurrent.ConcurrentLinkedQueue.offer(Unknown Source)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler$1.offer(Http11Protocol.java:551)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler$1.offer(Http11Protocol.java:568)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:632)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)

I tried to increase memory size on java start from
"-Xms256m -Xmx512m -XX:MaxPermSize=256m" to "-Xms512m -Xmx768m -XX:MaxPermSize=512m"
Even that doesn't helps.