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In order to implement check-pointing, I save the state of the scoreboards to disk, while processing the scoreboards for each flow-file. When the program starts for the first time, it checks for checkpoints on disk before starting the scoreboading of every direction and if a checkpoint is present it unmarshalls the data from the checkpoint and starts updating the scoreboards from that point on. 

Saving the Checkpoints 

Wiki MarkupThe first issue was how to save the state to disk. I decided to go with marshalling and saving the part of the [nested hash structure |http://users.telenet.be/jurgen.kobierczynski/jkflow/mylist.pdf] containing the current scoreboard to disk. Specifically, mylist \{direction\}\{$direction\} \{scoreboard\} \{aggregate\} \{report\} points to an array of nested hashes , one for each type of report defined  (as shown highlighted in the thumbnail below).  ( let $ref = mylist \{direction\}\{$direction\} \{scoreboard\} \{aggregate\} \{report\}\[$i\] for the $ith report type ).  Then $ref->\{aggdata\}\{tuplevalues\} contains a nested hash containing the current counters for the flows/packets/bytes both inward and outward for a particular 'direction'(Such as ATLAS BNL to CERN' ) specified by the $direction variable in structure  containing the current scoreboard to disk. Specifically, mylist {direction}{$direction} {scoreboard} {aggregate} {report} points to an array of nested hashes , one for each type of report defined  (as shown highlighted in the thumbnail below).  ( let $ref = mylist {direction}{$direction} {scoreboard} {aggregate} {report}[$i] for the $ith report type ).  Then $ref->{aggdata}{tuplevalues} contains a nested hash containing the current counters for the flows/packets/bytes both inward and outward for a particular 'direction'(Such as ATLAS BNL to CERN' ) specified by the $direction variable in mylist.

I create a temporary data strcuture ,each time the scoreboarding function is called in JKFlow.pm for a particular flowflile and then for a particular direction , and store the values of $ref->{aggdata}{tuplevalues} as well as certain other important variables representing the state of scoreboard including the $ref-> {count}, $ref->{startperiod}and $ref->{counter} in that data strcuture. It is then marshalled and written to disk using a module written in C called Storable. The technique i explained on this page. 

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