[jira] [Created] (HDFS-13639) SlotReleaser is not fast enough

["Gang Xie (JIRA)" <ji...@apache.org>]

Gang Xie created HDFS-13639:
-------------------------------

             Summary: SlotReleaser is not fast enough
                 Key: HDFS-13639
                 URL: https://issues.apache.org/jira/browse/HDFS-13639
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: hdfs-client
    Affects Versions: 3.0.2, 2.6.0, 2.4.0
         Environment: ------------------

YCSB:
 # {color:#000000}records
 recordcount=2000000000
 fieldcount=1
 fieldlength=1000
 operationcount=10000000
 
 workload=com.yahoo.ycsb.workloads.CoreWorkload
 
 table=ycsb-test
 columnfamily=C
 readproportion=1
 updateproportion=0
 insertproportion=0
 scanproportion=0
 
 maxscanlength=0
 requestdistribution=zipfian
 
 # default 
 readallfields=true
 writeallfields=true
 scanlengthdistribution=constant{color}{color:#000000}-------------------------------------------{color}{color:#000000}datanode:{color}{color:#000000}-Xmx2048m -Xms2048m -Xmn1024m -XX:MaxDirectMemorySize=1024m -XX:MaxPermSize=256m -Xloggc:$run_dir/stdout/datanode_gc_${start_time}.log -XX:+DisableExplicitGC -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=$log_dir -XX:+PrintGCApplicationStoppedTime -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=80 -XX:+UseCMSInitiatingOccupancyOnly -XX:+CMSParallelRemarkEnabled -XX:+CMSClassUnloadingEnabled -XX:CMSMaxAbortablePrecleanTime=10000 -XX:+CMSScavengeBeforeRemark -XX:+PrintPromotionFailure -XX:+CMSConcurrentMTEnabled -XX:+ExplicitGCInvokesConcurrent -XX:+SafepointTimeout -XX:MonitorBound=16384 -XX:-UseBiasedLocking -verbose:gc -XX:+PrintGCDetails -XX:+PrintHeapAtGC -XX:+PrintGCDateStamps{color}{color:#000000}------------------------------------------------{color}{color:#000000}regionserver:{color}{color:#000000}-Xmx10g -Xms10g -XX:MaxDirectMemorySize=10g -XX:MaxGCPauseMillis=150 -XX:MaxTenuringThreshold=2 -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=5 -Xloggc:$run_dir/stdout/regionserver_gc_${start_time}.log -Xss256k -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=$log_dir -verbose:gc -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCApplicationStoppedTime -XX:+PrintHeapAtGC -XX:+PrintGCDateStamps -XX:+PrintAdaptiveSizePolicy -XX:+PrintTenuringDistribution -XX:+PrintSafepointStatistics -XX:PrintSafepointStatisticsCount=1 -XX:PrintFLSStatistics=1 -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=100 -XX:GCLogFileSize=128m -XX:+SafepointTimeout -XX:MonitorBound=16384 -XX:-UseBiasedLocking -XX:+UseG1GC -XX:InitiatingHeapOccupancyPercent=65 -XX:+ParallelRefProcEnabled -XX:ConcGCThreads=4 -XX:ParallelGCThreads=16 -XX:G1HeapRegionSize=32m -XX:G1MixedGCCountTarget=64 -XX:G1OldCSetRegionThresholdPercent=5{color}{color:#000000}block cache is disabled:{color}{color:#000000} <property>
 <name>hbase.bucketcache.size</name>
 <value>0.9</value>
 </property>{color}

 
            Reporter: Gang Xie
             Fix For: 2.4.0
         Attachments: ShortCircuitCache_new_slotReleaser.diff, perf_after_improve_SlotReleaser.png, perf_before_improve_SlotReleaser.png

When test the performance of the ShortCircuit Read of the HDFS with YCSB, we find that SlotReleaser of the ShortCircuitCache has some performance issue. The problem is that, the qps of the slot releasing could only reach to 1000+ while the qps of the slot allocating is ~3000. This means that the replica info on datanode could not be released in time, which causes a lot of GCs and finally full GCs.

 

The fireflame graph shows that SlotReleaser spends a lot of time to do domain socket connecting and throw/catching the exception when close the domain socket and its streams. It doesn't make any sense to do the connecting and closing each time. Each time when we connect to the domain socket, Datanode allocates a new thread to free the slot. There are a lot of initializing work, and it's costly. We need reuse the domain socket. 

 

After switch to reuse the domain socket(see diff attached), we get great improvement(see the perf):
 # without reusing the domain socket, the get qps of the YCSB getting worse and worse, and after about 45 mins, full GC starts. When we reuse the domain socket, no full GC found, and the stress test could be finished smoothly, the qps of allocating and releasing match.
 # Due to the datanode young GC, without the improvement, the YCSB get qps is even smaller than the one with the improvement, ~3700 VS ~4200.

The diff is against 2.4, and I think this issue exists till latest version. I doesn't have test env with 2.7 and higher version. 



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