hbase_ycsb‘ result of overall Throughput is zero

After I ran about 10 hours `--benchmarks=hbase_ycsb`
I got invalid result with zero, but no error info

`overall Throughput 0.000000 ops/sec (clientbuffering="false" clients="32" command_line="Command line: -db com.yahoo.ycsb.db.HBaseClient10 -threads 32 -P /tmp/pkb/workloada -p clientbuffering=false -p columnfamily=cf -p recordcount=1000000 -p maxexecutiontime=1800 -p operationcount=1000000 -p measurementtype=histogram -t" readproportion="0.5" stage="run" threads_per_client_vm="32" updateproportion="0.5" workload_index="0" workload_name="workloada")
`