¶ Summary
- workload involves processing 100 pairs of large files using the same program (e.g., full-file comparisons). Each job takes approximately 6 minutes, resulting in a total sequential processing time of around 10 hours.
- The goal is to significantly reduce total execution time by exploiting the embarrassingly parallel nature of the task. The available infrastructure consists of 25 idle machines within a Windows domain, but introducing distributed workflow software is constrained by lengthy approval processes and limited administrative capacity.
- solution is designed using a lightweight approach: (1.) the windows tool PsExec.exe is employed to remotely launch jobs across the 25 machines without requiring full agent installations. (2.) GNU Make is used to orchestrate and parallelize the map tasks automatically within the script, ensuring efficient workload distribution. (3.) Redis as a queue manager.
An alternative option may be based on Spark. A Spark-based project is detailed here.
- The parallel execution strategy is expected to reduce total processing time to under 30 minutes, assuming minimal file transfer latency—achieving near-linear speedup relative to the number of available machines.
¶ Main solution
In case we have corporate policies that do not prevent us from installing software,
the most obvious solution may be based on Ansible,
who guarantees idempotency of task executions and an agentless architecture.
https://docs.ansible.com/ansible/latest/playbook_guide/playbooks_strategies.html
¶ Building the tech stack
The following Archimate diagram shows when our needs, at the top, meet the tech options, at the bottom, what is adopted and what is ruled-out:
a map-reduce work schedule, assuming 7 map-tasks and 4 nodes:
E-R diagram of the entities used by the orchestrator (GNU make):
NB
- in such map-reduce scenarios, each file serves as either the input or the output of exactly one task.
- we limit workers to one task at a time.
sequence diagram of the actions performed by each map task:
NB: again, nothing needs to be deployed on the workers machines, except for the input and output data files.
deployment diagram:
The Makefile that defines the steps and the dependencies of the whole process is available at this link:
https://github.com/a-moscatelli/home/blob/main/am-wiki-assets/mapreducewin/Makefile
Based on the Makefile above, we just run:
set PARALLEL_DEGREE=3
make install
make initialize
make -j %PARALLEL_DEGREE% all
The activity log, with five 1-minute long map jobs and 3 nodes, is as below:
23:24:56.16 EXEC_ initialize
23:25:01.78 BEGIN TASK001.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:01.84 BEGIN TASK002.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:01.86 BEGIN TASK003.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:05.97 END__ TASK001.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:06.05 BEGIN TASK004.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:06.11 END__ TASK002.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:06.13 END__ TASK003.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:06.19 BEGIN TASK005.step1.workerAcquisitionLoopFinished.mkcontrol
23:25:06.28 BEGIN TASK001.step2.inputFilePushedToWorker.mkcontrol HOST003
23:25:06.46 BEGIN TASK002.step2.inputFilePushedToWorker.mkcontrol HOST002
23:25:06.64 BEGIN TASK003.step2.inputFilePushedToWorker.mkcontrol HOST001
23:25:06.87 BEGIN TASK001.step3.submittedToWorker.mkcontrol HOST003
23:25:07.40 BEGIN TASK002.step3.submittedToWorker.mkcontrol HOST002
23:25:07.91 BEGIN TASK003.step3.submittedToWorker.mkcontrol HOST001
23:26:09.53 END__ TASK001.step4.workerCompletionCheckLoopFinished.mkcontrol HOST003
23:26:09.67 END__ TASK002.step4.workerCompletionCheckLoopFinished.mkcontrol HOST002
23:26:09.82 END__ TASK003.step4.workerCompletionCheckLoopFinished.mkcontrol HOST001
23:26:15.17 END__ TASK004.step1.workerAcquisitionLoopFinished.mkcontrol
23:26:15.28 BEGIN TASK004.step2.inputFilePushedToWorker.mkcontrol HOST003
23:26:15.30 END__ TASK005.step1.workerAcquisitionLoopFinished.mkcontrol
23:26:15.44 BEGIN TASK005.step2.inputFilePushedToWorker.mkcontrol HOST002
23:26:15.51 BEGIN TASK004.step3.submittedToWorker.mkcontrol HOST003
23:26:15.65 BEGIN TASK005.step3.submittedToWorker.mkcontrol HOST002
23:27:16.85 END__ TASK004.step4.workerCompletionCheckLoopFinished.mkcontrol HOST003
23:27:16.97 END__ TASK005.step4.workerCompletionCheckLoopFinished.mkcontrol HOST002
23:27:17.00 BEGIN reduce
23:27:17.08 END__ reduce
links:
- https://learn.microsoft.com/en-us/sysinternals/downloads/psexec
the agent that makes remote calls - https://www.gnu.org/software/make/manual/
the agent that enables the parallel executions
the semaphore, required to ensure that only one process at a time can acquire a worker node, is based on the success/failure of a file rename.
Such option does not handle well the possibility that a lock holder will not survive the moment it is supposed to release the lock for other purposes.
a solution can be easily implemented using redis:
#docker
image: "redis:6.0.9"
Windows client:
https://github.com/microsoftarchive/redis/releases
example of a working script:
set REDISCLI=.\Redis-x64-3.0.504\redis-cli.exe
set REDISSERVERHOST=DESKTOP-B12345T
set REDIS_CALL=%REDISCLI% -h %REDISSERVERHOST% -p 6379
%REDISCLI% -h %REDISSERVERHOST% -p 6379 PING
rem > PONG
echo %ERRORLEVEL%
rem > 0
set autoexpire_seconds=600
set key=HOST1
set val=TASK4
rem simulation of a lock acquisition"
%REDIS_CALL% SET %key% %val% EX %autoexpire_seconds% NX
rem > OK
rem simulation of a competing concurrent lock acquisition:
%REDIS_CALL% SET %key% %val% EX %autoexpire_seconds% NX
rem > (nil)
%REDIS_CALL% KEYS "*"
rem > 1) "HOST1"
rem simulation of a lock release:
%REDIS_CALL% DEL %key%
rem > (integer) 1
%REDIS_CALL% KEYS "*"
rem > (empty list or set)
%ERRORLEVEL% after each CLI call above is always 0
¶
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