The first completed implementation in the new refactorised scoreboarding code is a scheme for checkpointing and crash-recovery of the scoreboards and alignment of the scoreboarding with regular clock-hours/day-periods. Both of these improvements are discussed below:
CheckPointing
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
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The 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 mylist. |
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This is the top level of the score directory for the 'USATLAS Computing Farm - CERN' direction. There are four checkpoints in this directory. The starting number before the checkpoint is the duration in minutes of the report-type (as defined in JKFlow.xml) for this checkpoint. Thus 1440checkpoint.dat is the checkpoint for the daily aggregate report type and 360checkpoint.dat is the checkpoint for the six-hourly report.
Loading the Checkpoints
The checkpoints only need to be loaded at the start of the program run. For this purpose I have a variable called FIRSTTIME which has module-wide visibility for all objects of JKFlow. THe value of this variable is default to 0 and set to 1 after the first flow-file has been processed. Thus I can load the checkpoint (if present) for the first run of the program.
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In this way if the machine crashes and is restarted the scoreboarding would be started from the exact same point where it was left off.