Rajat Khandelwal created LENS-1169:
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Summary: Stopping Query Service is incorrect
Key: LENS-1169
URL: https://issues.apache.org/jira/browse/LENS-1169
Project: Apache Lens
Issue Type: Bug
Reporter: Rajat Khandelwal
Assignee: Rajat Khandelwal
Stopping lens server basically stops all services. For query service, the
current flow is this:
* Preapre stopping:
** Interrupt All threads (query submitter, purger, status poller etc)
* Persist state
* Stop
** join all threads ( as mentioned above)
Each of the threads is basically running in a large loop like the following:
{noformat}
while (!stopped && !this.isInterrupted()) {
try {
} catch(InterruptedException) {
return
}
}
{noformat}
Now, interrupting a thread will cause InterruptException in the thread only
when the thread is waiting/sleeping.
So, the thread can exit in two ways:
* By receiving interrupt
* If an interrupt isn't received, it'll complete the current iteration loop and
then exit.
So there can be a scenario like the following (I faced such a scenario while
working on LENS-904):
* Stop is called from outside
* Prepare stopping. Let's say QuerySubmitter didn't receive the interrupt and
will exit after completing its current iteration.
* Persist:
** Persist part1: Persisting driver states. e.g. HiveDriver keeps a map of
query handle to hive operation handle.
* QuerySubmitter submits the query to hive, changes the state of query to
LAUNCHED and exits.
* Persist:
** Persist part 2: Persisting queries. This persists the query mentioned in
the above point as LAUNCHED.
Now, on start, the states will be read back, query's state will be LAUNCHED,
and HiveDriver won't have the operation handle corresponding to this query.
This will cause the query to fail in next status update.
Proposed Solution:
Interrupt and join the threads before persisting in the prepareStopping phase.
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