Calendar server often throws exception: "canceling statement due to statement timeout"

My Calendar server in Server.app 5.0.15 on 10.10.5 pretty consistently throws the following exception:

2016-04-19 16:23:54+1000 [-] [caldav-1] [-] [twext.enterprise.jobs.jobitem#error] JobItem: 2693107, WorkItem: 2693107 failed: [Failure instance: Traceback: <class 'pg8000.core.ProgrammingError'>: (u'ERROR', u'57014', u'canceling statement due to statement timeout', u'SQL statement "SELECT 1 FROM ONLY "public"."calendar_object" x WHERE "resource_id" OPERATOR(pg_catalog.=) $1 FOR KEY SHARE OF x"', u'postgres.c', u'2970', u'ProcessInterrupts', u'', u'')

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twisted/internet/defer.py:588:_runCallbacks

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twisted/internet/defer.py:1184:gotResult

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twisted/internet/defer.py:1126:_inlineCallbacks

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twisted/python/failure.py:389:throwExceptionIntoGenerator

2016-04-19 16:23:54+1000 [-] [caldav-1] --- <exception caught here> ---

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twext/enterprise/jobs/jobitem.py:445:run

2016-04-19 16:23:54+1000 [-] [caldav-1] /Applications/Server.app/Contents/ServerRoot/Library/CalendarServer/lib/python2 .7/site-packages/twisted/internet/defer.py:1126:_inlineCallbacks

It doesn't seem to affect functionality, but it pollutes the logs every 30 seconds with this.

Does the actual SQL statement of "SELECT 1 FROM ONLY "public"."calendar_object" x WHERE "resource_id" OPERATOR(pg_catalog.=) $1 FOR KEY SHARE OF x" shed any light?

Thanks.