12:25 p.m.
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https://issues.jboss.org/browse/JBJCA-676?page=com.atlassian.jira.plugin....
]
Jeremy Whiting commented on JBJCA-676:
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Some research into the LIRS eviction policy has revealed the cause of the closed
statement exceptions. LIRS splits the cache into two sections called 'high' and
'low'. An item is located in each section depending on it's recency (how often
and how recently) it is accessed.
The org.jboss.jca.adapters.jdbc.util.BoundedConcurrentHashMap object provides an
EvictionListener and each eviction policy implements the onEntryEviction(evicted) method.
The implementation of this listener closes the underlying PreparedStatement. See
org.jboss.jca.adapters.jdbc.PreparedStatementCache.PreparedStatementEvictionListener.
What distinguishes the LIRS to the LRU policy is when the onEntryEviction is called. With
LRU the eviction listener will be called when the least used item is evicted. But with
LIRS the listener is also called when an item is demoted from 'low' to the
'high' section. The item remains in the cache and is not flushed. This means the
PreparedStatementCache will have an item which is marked as closed. This is a problem in
the current PreparedStatementCache because an item is not checking it's closed status
before passing the object to the caller of prepareStatement(...).
To prove these finding a junit test case is provided demonstrating the behaviour of the
cache. It is a Maven project and the test case is called using the normal plugin call, $
mvn test
The test will fail on the last assert statement showing the mock PreparedStatement was
closed by the cache. Even though it remains in the cache.
Evicted and closed CachedPreparedStatement leased out again on next
call to prepareStatement by LIRS cache.
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Key: JBJCA-676
URL: https://issues.jboss.org/browse/JBJCA-676
Project: IronJacamar
Issue Type: Bug
Components: JDBC
Affects Versions: 1.0.4.Final
Environment: Using MySQL5 database on linux.
Reporter: Jeremy Whiting
Assignee: Jesper Pedersen
Attachments: added-logging-messages.diff, as7.1-server-log-extract.txt
My application throws an exception that reports the PreparedStatement cannot be used
after it is closed. The exception is
javax.persistence.PersistenceException: org.hibernate.exception.JDBCConnectionException:
No operations allowed after statement closed.
It appears the PreparedStatementCache is not flushing an evicted item from the cache.
The cache does call PreparedStatementEvictionListener.onEntryEviction(Map) which closes
all the cached items being evicted. But it does not remove the item from the cache in that
same call.
When a client then calls prepareStatement(String) using the identical sql as a cached
item the lookup in the cache returns the closed CachedPreparedStatement.
I have a test case that calls the transaction on the server. The client makes an EJB
call using a web service endpoint. The test case only executes one client call at a time.
Observed behaviour
This behaviour has only been seen to occur when eviction and prepare call are for
identical SQL and when no other JDBC work happens between the two calls. Additionally it
is timing sensitive. Turning on DEBUG logging makes the issue go away. To generate the
logs attached I used a ramdisk and an ASYNC logging appender to eliminate delays due to
saving to disk.
Attached are logs with DEBUG level messages turned on for these categories:
org.hibernate.SQL, org.hibernate.engine.jdbc.internal.JdbcResourceRegistryImpl and
jboss.jdbc.spy
To highlight the behaviour I added two logging messages. Source files are attached as a
diff.
a) The first is when items in the cache are evicted. The log message shows the hash
identity of the CachedPreparedStatement and the SQL statement. Message added to
org.jboss.jca.adapters.jdbc.PreparedStatementCache.onEntryEviction(Map) on line 255.
b) The second is just before the first parameter (a String) is bound to a
PreparedStatement. The message logs the hash identity of the CachedPreparedStatement, the
SQL and hashed identity of the underlying driver com.mysql.jdbc.JDBC4PreparedStatement.
The message is added to
org.jboss.jca.adapters.jdbc.WrappedPreparedStatement.setString(int, String) on line 637
The log file shows the two events that match the behaviour detailed earlier. The log
file is an small extract of the original. The first (the eviction) on line 21 and the
second (the parameter binding) on 24.
A test case will follow with an attempt to use H2 rather than MySQL.
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