Backfill function throughput is low.

[gnumoreno]

For some odd reason the throughput for the backfill function is much lower then for writes. I'm using the same concurrency.

Test was conducted with the following setup:

• Scylla Cluster - 3 nodes i3.8xlarge
• NDBench cluster - 5 nodes m4.10xlarge
• NDBench cluster deployed using ansible https://github.com/gnumoreno/NdbenchAWS

application.properties has following:
ndbench.config.numKeys=250000000
ndbench.config.writeRateLimit=400000
ndbench.config.readRateLimit=500000
ndbench.config.numValues=50000
ndbench.config.dataSize=1024
ndbench.config.numWriters=1000
ndbench.config.numReaders=1000
ndbench.config.backfillStartKey=1
ndbench.config.numBackfill=1000
ndbench.config.cass.host=172.31.31.228
ndbench.config.cass.keyspace=ndbench
ndbench.config.cass.cfname=scylla
ndbench.config.cass.cluster=NDBench
ndbench.config.cass.colsPerRow=6
ndbench.config.cass.writeConsistencyLevel=ONE
ndbench.config.cass.readConsistencyLevel=ONE
ndbench.config.cass.connections=32

I noticed that the backfill function is very verbose printing each key that is inserted to stdout or (in this case) to the catalina.out file while the writeSingle function just prints the summary with WPS. I wonder if this is the reason why the backfill is able to reach just 40k wps thorughput while writes are over 100k wps.