[Bug 2040] New: Improve HarvesterHelper.collectAndSaveThreadData()

[bugzilla-daemon at icedtea.classpath.org]

http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=2040

            Bug ID: 2040
           Summary: Improve HarvesterHelper.collectAndSaveThreadData()
           Product: Thermostat
           Version: hg
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P5
         Component: Thermostat
          Assignee: unassigned at icedtea.classpath.org
          Reporter: sgehwolf at redhat.com
                CC: thermostat at icedtea.classpath.org
            Blocks: 2038

HarvesterHelper.collectAndSaveThreadData() calls the following in a loop (n ==
number of threads of a JVM):
 - ThreadHeaderHelper.checkAndSaveThreadHeader(): performs 1 query + 1 add
 - ThreadStateHelper.saveThreadState(): performs 1 query + 1 add or update
 - ThreadContentionHelper.saveContentionSample(): performs 1 add.

Thus, 2 + 2 + 1 = O(5n) DB ops (reads and/or writes). This way the # of queries
depend on the # of threads.

A few avenues worth exploring are:
 1.) Remove query part. Agent doing querying is bad practice.
 2.) If 1 is not possible refactor the query to fetch all thread headers for
all
     threads in one query. This might need projection support.
 3.) Consider implementing API for bulk writes. It's worth saving a network
round-trip. I.e. send a list (cardinality n) of thread headers/contention
samples to get inserted.

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