https://issues.apache.org/jira/browse/AMQ-3397: Improve scalability of active durable subs with JDBC message store. Cache topic message sequence ids to avoid each ack going to the store twice, boost through put for active durable subs; 100 subs, 550->2200 for 2min test with mysql
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/store/jdbc/JDBCMessageStore.java