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Apache Gobblin is Hadoop ingestion software used at WMF primarily to import data from Kafka into HDFS.
WMF's Gobblin fork
The Data Engineering team maintains a fork of Gobblin. The master branch should track upstream and our own gobblin-wmf gobblin module in the wmf branch. The gobblin-wmf module mostly contains code to ingest Kafka events to HDFS.
Releasing new Gobblin versions
Build the gobblin-wmf jar
In the gobblin source folder, run:
./gradlew :gobblin-modules:gobblin-wmf:shadow. This creates multiple jars in the
build/gobblin-wmf/libs subfolder, and the one to be used for execution is named as in
all mention that the jar is a fat-jar, containing all the needed dependencies to be executed.
Upload the jar to Archiva
We upload our gobblin-wmf artifacts directly to Archiva, and then add them as git-fat jar files in Analytics/Systems/Cluster/Deploy/Refinery, and deploy them like we do other jar artifacts with analytics/refinery.
We do not (as of 2021-07) have an automated release process for Gobblin. You must manually upload the packaged artifact .jars to archiva, and manually download and git add them to analytics/refinery.
Pulling from Kafka
We experienced regular inconsistencies in volumes of data pulled from Kafka in the first month of usage of Gobblin. More precisely, it happened regularly that some pull-tasks (executed in map-containers) were actually not pulling any data while they were expected to do so. This didn't lead to Gobblin job-errors, just delay in pulling some data. Unfortunately, due to how we trigger computation jobs after data is pulled, the problem led to data-loss alerts when the phenomenon occurred just after the hour. We investigated and found why some tasks were failing to pull data: there is a specific settings making Gobblin time-out (without error, just no data) when fetching it's first batch of data from kafka. Details can be found in that task: https://phabricator.wikimedia.org/T290723.
Gobblin metrics are not easy to grasp. In particular they embed a
Context notion (as tag) that details from how deep in the gobblin-architecture the metrics is generated. In our usage of gobblin, here are some findings:
- The Gobblin CLI process and every Gobblin map-task are different metrics context (the map-tasks have the same job-id tag)
- There are many contexts in which metrics are generated, making it not easy to define which to get (for our use case, it seems that contexts of the form: metricContextName=gobblin.metrics.job_JOBNAME_JOBTS are the ones summarizing all the values of interest).
- Metrics are generated during the task execution with intermediate values, and the last generated metric-event is flagged as