Merge pull request #214 from LatencyUtils:master

    [core] use HdrHistogram and fix coordinated omission

also closes #10

core/CHANGES.md

@@ -0,0 +1,67 @@
+When used as a latency under load benchmark YCSB in it's original form suffers from
+Coordinated Omission[1] and related measurement issue:
+
+* Load is controlled by response time
+* Measurement does not account for missing time
+* Measurement starts at beginning of request rather than at intended beginning
+* Measurement is limited in scope as the histogram does not provide data on overflow values
+
+To provide a minimal correction patch the following were implemented:
+
+1. Replace internal histogram implementation with HdrHistogram[2]:
+HdrHistogram offers a dynamic range of measurement at a given precision and will
+improve the fidelity of reporting. It allows capturing a much wider range of latencies.
+HdrHistogram also supports compressed loss-less serialization which enable capturing
+snapshot histograms from which lower resolution histograms can be constructed for plotting
+latency over time. Snapshot interval histograms are serialized on status reporting which
+must be enabled using the '-s' option.
+
+2. Track intended operation start and report latencies from that point in time:
+Assuming the benchmark sets a target schedule of execution in which every operation
+is supposed to happen at a given time the benchmark should measure the latency between
+intended start time and operation completion.
+This required the introduction of a new measurement point and inevitably
+includes measuring some of the internal preparation steps of the load generator.
+These overhead should be negligible in the context of a network hop, but could
+be corrected for by estimating the load-generator overheads (e.g. by measuring a
+no-op DB or by measuring the setup time for an operation and deducting that from total).
+This intended measurement point is only used when there is a target load (specified by
+the -target paramaeter)
+
+This branch supports the following new options:
+
+* -p measurementtype=[histogram|hdrhistogram|hdrhistogram+histogram|timeseries] (default=histogram)
+The new measurement types are hdrhistogram and hdrhistogram+histogram. Default is still
+histogram, which is the old histogram. Ultimately we would remove the old measurement types
+and use only HdrHistogram but the old measurement is left in there for comparison sake.
+
+* -p measurement.interval=[op|intended|both] (default=op)
+This new option deferentiates between measured intervals and adds the intended interval(as described)
+above, and the option to record both the op and intended for comparison.
+
+* -p hdrhistogram.fileoutput=[true|false] (default=false)
+This new option will enable periodical writes of the interval histogram into an output file. The path can be set using '-p hdrhistogram.output.path=<PATH>'.
+
+Example parameters:
+-target 1000 -s -p workload=com.yahoo.ycsb.workloads.CoreWorkload -p basicdb.verbose=false -p basicdb.simulatedelay=4 -p measurement.interval=both -p measurementtype=hdrhistogram -p hdrhistogram.fileoutput=true -p maxexecutiontime=60
+
+Further changes made:
+
+* -p status.interval=<number of seconds> (default=10)
+Controls the number of seconds between status reports and therefore between HdrHistogram snapshots reported.
+
+* -p basicdb.randomizedelay=[true|false] (default=true)
+Controls weather the delay simulated by the mock DB is uniformly random or not.
+
+Further suggestions:
+
+1. Correction load control: currently after a pause the load generator will do
+operations back to back to catchup, this leads to a flat out throughput mode
+of testing as opposed to controlled load.
+
+2. Move to async model: Scenarios where Ops have no dependency could delegate the
+Op execution to a threadpool and thus separate the request rate control from the
+synchronous execution of Ops. Measurement would start on queuing for execution.
+
+1. https://groups.google.com/forum/#!msg/mechanical-sympathy/icNZJejUHfE/BfDekfBEs_sJ
+2. https://github.com/HdrHistogram/HdrHistogram

core/pom.xml

@@ -32,6 +32,33 @@
       <version>6.1.1</version>
       <scope>test</scope>
     </dependency>
-  </dependencies>	
-
+    <dependency>
+      <groupId>org.hdrhistogram</groupId>
+      <artifactId>HdrHistogram</artifactId>
+      <version>2.1.4</version>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <version>${maven.assembly.version}</version>
+        <configuration>
+          <descriptorRefs>
+            <descriptorRef>jar-with-dependencies</descriptorRef>
+          </descriptorRefs>
+          <appendAssemblyId>false</appendAssemblyId>
+        </configuration>
+        <executions>
+          <execution>
+            <phase>package</phase>
+            <goals>
+              <goal>single</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

core/src/main/java/com/yahoo/ycsb/BasicDB.java

@@ -22,6 +22,8 @@
 import java.util.Set;
 import java.util.Enumeration;
 import java.util.Vector;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.LockSupport;
 
 
 /**
@@ -32,11 +34,15 @@ public class BasicDB extends DB
 	public static final String VERBOSE="basicdb.verbose";
 	public static final String VERBOSE_DEFAULT="true";
 
-	public static final String SIMULATE_DELAY="basicdb.simulatedelay";
-	public static final String SIMULATE_DELAY_DEFAULT="0";
+    public static final String SIMULATE_DELAY="basicdb.simulatedelay";
+    public static final String SIMULATE_DELAY_DEFAULT="0";
+
+    public static final String RANDOMIZE_DELAY="basicdb.randomizedelay";
+    public static final String RANDOMIZE_DELAY_DEFAULT="true";
+
 
-	
-	boolean verbose;
+    boolean verbose;
+    boolean randomizedelay;
 	int todelay;
 
 	public BasicDB()
@@ -49,14 +55,22 @@ void delay()
 	{
 		if (todelay>0)
 		{
-			try
-			{
-				Thread.sleep((long)Utils.random().nextInt(todelay));
-			}
-			catch (InterruptedException e)
-			{
-				//do nothing
-			}
+		    long delayNs;
+		    if (randomizedelay) {
+		        delayNs = TimeUnit.MILLISECONDS.toNanos(Utils.random().nextInt(todelay));
+		        if (delayNs == 0) {
+		            return;
+		        }
+		    }
+		    else {
+		        delayNs = TimeUnit.MILLISECONDS.toNanos(todelay);
+		    }
+
+		    long now = System.nanoTime();
+            final long deadline = now + delayNs;
+            do {
+                LockSupport.parkNanos(deadline - now);
+            } while ((now = System.nanoTime()) < deadline && !Thread.interrupted());
 		}
 	}
 
@@ -69,7 +83,7 @@ public void init()
 	{
 		verbose=Boolean.parseBoolean(getProperties().getProperty(VERBOSE, VERBOSE_DEFAULT));
 		todelay=Integer.parseInt(getProperties().getProperty(SIMULATE_DELAY, SIMULATE_DELAY_DEFAULT));
-
+		randomizedelay=Boolean.parseBoolean(getProperties().getProperty(RANDOMIZE_DELAY, RANDOMIZE_DELAY_DEFAULT));
 		if (verbose)
 		{
 			System.out.println("***************** properties *****************");