[Building Sakai] Portfolio creation crash

[Joshua Swink]

When several people try to create portfolios at the same time, Sakai
crashes. I'm using version 2.6.0.

The problems are:

- Sakai crashes with connection pool errors. That is, it becomes
unresponsive and Tomcat must be killed.
- The pool, load balanced with mod_jk, becomes entirely unresponsive.
The remaining Tomcats are fine (they can be accessed directly). When
the misbehaving Tomcat is killed, the pool recovers and the other
instances can be used again.

Questions

1) Does anyone have insight into this error?
2) How can we make the pool continue to operate even when one Tomcat
is misbehaving this way? We are using mod_jk version 1.20, and
considering updating it.

In the logs, there's no hint of trouble until a string of exceptions
like the following occurs. The actual select statement varies.

2009-09-22 14:39:46,417  WARN TP-Processor620
org.hibernate.util.JDBCExceptionReporter - SQL Error: 0, SQLState:
null
2009-09-22 14:39:46,418 ERROR TP-Processor620
org.hibernate.util.JDBCExceptionReporter - Cannot get a connection,
pool error Timeout waiting for idle object
2009-09-22 14:39:47,052  WARN TP-Processor895
org.sakaiproject.db.impl.BasicSqlService - Sql.dbRead: sql: select
AX.SESSION_ID,AX.SESSION_SERVER,AX.SESSION_USER,AX.SESSION_IP,AX.SESSION_HOSTNAME,AX.SESSION_USER_AGENT,AX.SESSION_START,AX.SESSION_END,AX.SESSION_ACTIVE
from   SAKAI_SESSION AX inner join SAKAI_PRESENCE A ON AX.SESSION_ID =
A.SESSION_ID where A.LOCATION_ID = ? 200930-1545-LIT-030-01-presence
org.apache.commons.dbcp.SQLNestedException: Cannot get a connection,
pool error Timeout waiting for idle object
    at org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:104)


Joshua Swink