hibernate/hibernate-orm — pull request #433 by nshestakov (2012-12-28 18:20:58+00:00)
Title: using ConcurrentHashMap for decrease locking in JTASessionContext

JTASessionContext used Hashtable for associate transaction to session. It is slow for hige-load applications (many threads wait synchronization on Hastable).
ConcurrentHashMap remove this trouble.