https://bz.apache.org/bugzilla/show_bug.cgi?id=59849
Bug ID: 59849
Summary: initSQL not executed when JDBC connection created
under load
Product: Tomcat Modules
Version: unspecified
Hardware: PC
OS: Solaris
Status: NEW
Severity: normal
Priority: P2
Component: jdbc-pool
Assignee: dev@tomcat.apache.org
Reporter: christian.klau...@adnovum.ch
Tomcat: 7.0.57
OS: SunOS HOST 5.10 Generic_150401-20 i86pc i386 i86pc
$ java -version
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)
Our application relies on initSQL to set the current_schema on each JDBC
connection. We noticed that when our application is under heavy load (maxActive
DB connections), the application sometimes gets handed a connection that did
not have initSQL executed on it.
We had a look at the ConnectionPool.java source code (TOMCAT_7_0_57 and trunk)
and found that there is a scenario where the pool creates a new connection
without running `PooledConnection#validate(PooledConnection.VALIDATE_INIT)` on
it.
To reproduce this issue, two conditions need to coincide:
1) The server has to be under load. The pool needs to be saturated to the point
where no new connections get created for incoming requests (requests >
maxActive). Threads block on the 'idle' queue/the waitcount atomic is > 0.
2) Active connections need to be released from the pool (unhandled exceptions,
maxAge, suspectTimeout etc.)
Under load, the ConnectionPool#release method will create an 'ad-hoc'
connection to replace the active connection it just removed from the
ConnectionPool:
if (waitcount.get() > 0) {
idle.offer(create(true));
}
The #connect call for a PooledConnection object created this way follows in
#borrowConnection instead of #createConnection. In #borrowConnection there is
no call to #validate(VALIDATE_INIT) before that 'ad-hoc' connection is returned
to the requesting thread.
Our best "workaround" at the moment:
- Use a validationQuery that fails when initSQL was not run
- enable testOnBorrow
- validationInterval at 1ms
The short validation interval is necessary because the 'ad-hoc' connection
object will have its lastValidation time stamp set to currentTimeMillis on
object creation, causing it to skip onBorrow validation immediately after it is
being created.
Needless to say this workaround comes at a significant performance cost to the
entire application (short validationInterval) in addition to creating those
uninitialized DB connections just to throw them away immediately when they
inevitably fail onBorrow validation.
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