0035886: MobileServerController.getThisServerDefinition creates contention

Description

MobileServerController.getThisServerDefinition method is invoked all the time from many different places. It is synchronized on a singleton class, which in practice, means there is only thread per JVM that can execute it.

This method causes some contention at JVM level.

The situation can become worse in scenarios with overload, if number of DB connections is limited at pool level. Because in some cases, the connection for the thread is borrowed from pool inside this method, this can cause deadlock situations if:

-pool size=1
-thread 1 acquires the connection anywhere
-thread 2 inside this method tries to get a new connection, it cannot get it till thread 1 returns the one it previously borrowed
-thread 1 invokes MobileServerController.getThisServerDefinition
-> DEADLOCK: it won't be able to execute this method till thread 2 completes it, but it is waiting for thread 1 to release its connection

Steps To Reproduce

Can be artificially reproduced by

0. Configure pool as follows:
db.pool.maxActive=5
db.pool.maxWait=10000
1. clone https://bitbucket.org/gpscode/butmultiservertests [^]
2. execute wordDay.jmx setting 10 concurrent threads
3. check JVM contention (attached a screenshot from Yourkit)

Proposed Solution

* Does it make any sense this method to be synchronized?
- If it does not: remove syncrhonization
- If it does: what for? would it properly work in a clustered environment?, in any case look for an alternative

* Additionally, always it's invoked a DB query is triggered, to always return the same record. Could we improve it by some caching?

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blocks

defect

0035754

closed

AugustoMauch

MobileServerController.getThisServerDefinition creates contention

Notes
(0097294) mtaal (manager) 2017-06-09 21:09	no need to backport, is covered in q3, individual backports will be done to but

Issue History
Date Modified	Username	Field	Change
2017-05-01 17:24	mtaal	Type	defect => backport
2017-05-01 17:24	mtaal	Target Version	=> RR17Q2.1
2017-05-01 17:25	mtaal	Assigned To	AugustoMauch => mtaal
2017-06-09 21:09	mtaal	Note Added: 0097294
2017-06-09 21:09	mtaal	Status	scheduled => closed
2017-06-09 21:09	mtaal	Resolution	open => no change required