Re: OLAP, Hadoop, Spark and Cassandra


Answering my own question - turned out I had had a mixup of keyspaces used between the two instances

Default the conf/hadoop-graph/ reads

While for CQL it should read

Also - as I made a 'named' (ve_graph) graph I had to point to that one rather than the janusgraph keyspace.

Problem 1 solved. Now to the next - how can I lower the number of 'partitions' Spark is using (here 796  '... on localhost (executor driver) (769/769)')?  

On Wednesday, December 4, 2019 at 11:46:42 PM UTC+1, Sture Lygren wrote:

I'm trying to get JanusGraph 0.4.0 with a Cassandra (CQL) backend setup and running as OLAP while still keeping OLTP active in order to do graph updates. I've been searching high and low for some guidance, but so far without any luck. Hopefully someone here could tune in and help?

Here's where I'm at currently

  • local Hadoop running according to
  • gremlin server started as /bin/ conf/gremlin-server/gremlin-server-configuration.yaml
  • gremlin-server-configuration.yaml points to init.groovy script doing the traversal mappings for OLTP and OLAP
def globals = [:]
ve ="ve_graph")
OLAPGraph ='conf/hadoop-graph/')
globals << [g : ve.traversal(), sg: OLAPGraph.traversal().withComputer(]
  • conf/hadoop-graph/ reads
  • Running the gremlin shell I have
         (o o)
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/data/sture/Scripts/janusgraph-0.4.0-hadoop2/lib/slf4j-log4j12-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/data/sture/Scripts/janusgraph-0.4.0-hadoop2/lib/logback-classic-1.1.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
plugin activated: tinkerpop.server
plugin activated: tinkerpop.tinkergraph
plugin activated: tinkerpop.hadoop
plugin activated: tinkerpop.spark
plugin activated: tinkerpop.utilities
plugin activated: janusgraph.imports
gremlin> :remote connect tinkerpop.server conf/remote.yaml session
==>Configured localhost/[655848fc-b46e-40be-8174-f0dc42cdabd4]
gremlin> :remote console
==>All scripts will now be sent to Gremlin Server - [localhost/]-[655848fc-b46e-40be-8174-f0dc42cdabd4] - type ':remote console' to return to local mode
gremlin> g
==>graphtraversalsource[standardjanusgraph[cql:[]], standard]
gremlin> sg
==>graphtraversalsource[hadoopgraph[cqlinputformat->gryooutputformat], sparkgraphcomputer]
gremlin> g.V().has('lbl','System').count()
gremlin> sg.V().has('lbl','System').count()
  • The job is running for some time and while finishing the gremlin-server.log reads
253856 [Executor task launch worker for task 768] INFO  org.apache.spark.executor.Executor  - Finished task 768.0 in stage 0.0 (TID 768). 2388 bytes result sent to driver
253858 [task-result-getter-1] INFO  org.apache.spark.scheduler.TaskSetManager  - Finished task 768.0 in stage 0.0 (TID 768) in 6809 ms on localhost (executor driver) (769/769)
253861 [dag-scheduler-event-loop] INFO  org.apache.spark.scheduler.DAGScheduler  - ResultStage 0 (fold at finished in 161.427 s
253861 [task-result-getter-1] INFO  org.apache.spark.scheduler.TaskSchedulerImpl  - Removed TaskSet 0.0, whose tasks have all completed, from pool
253876 [SparkGraphComputer-boss] INFO  org.apache.spark.scheduler.DAGScheduler  - Job 0 finished: fold at, took 161.598267 s
253888 [SparkGraphComputer-boss] INFO  org.apache.spark.rdd.MapPartitionsRDD  - Removing RDD 1 from persistence list
253901 [block-manager-slave-async-thread-pool-0] INFO  - Removing RDD 1
  • However - the count (==> ) reads 0 for the sg traversal
I've most likely missed some crucial point here, but I'm not able to spot it. Please help.

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