make --hdr_digits configurable

engine-api/src/main/java/io/nosqlbench/engine/api/metrics/ActivityMetrics.java

@@ -18,6 +18,7 @@
 package io.nosqlbench.engine.api.metrics;
 
 import com.codahale.metrics.*;
+import io.nosqlbench.engine.api.activityapi.core.Activity;
 import io.nosqlbench.engine.api.activityapi.core.MetricRegistryService;
 import io.nosqlbench.engine.api.activityimpl.ActivityDef;
 import io.nosqlbench.engine.api.util.Unit;
@@ -43,6 +44,16 @@ public class ActivityMetrics {
     };
     private static List<MetricsCloseable> metricsCloseables = new ArrayList<>();
 
+    private static int significantDigits = 4;
+
+    public static int getSignificantDigits() {
+        return significantDigits;
+    }
+
+    public static void setHdrDigits(int hdrDigits) {
+        ActivityMetrics.significantDigits = hdrDigits;
+    }
+
     private ActivityMetrics() {
     }
 
@@ -98,7 +109,7 @@ public class ActivityMetrics {
     public static Timer timer(ActivityDef activityDef, String name) {
         String fullMetricName = activityDef.getAlias() + "." + name;
         Timer registeredTimer = (Timer) register(activityDef, name, () ->
-                new NicerTimer(fullMetricName, new DeltaHdrHistogramReservoir(fullMetricName, 4)));
+                new NicerTimer(fullMetricName, new DeltaHdrHistogramReservoir(fullMetricName, significantDigits)));
         return registeredTimer;
     }
 
@@ -114,7 +125,7 @@ public class ActivityMetrics {
     public static Histogram histogram(ActivityDef activityDef, String name) {
         String fullMetricName = activityDef.getAlias() + "." + name;
         return (Histogram) register(activityDef, name, () ->
-                new NicerHistogram(fullMetricName, new DeltaHdrHistogramReservoir(fullMetricName, 4)));
+                new NicerHistogram(fullMetricName, new DeltaHdrHistogramReservoir(fullMetricName, significantDigits)));
     }
 
     /**

engine-cli/src/main/java/io/nosqlbench/engine/cli/NBCLI.java

@@ -81,6 +81,8 @@ public class NBCLI {
 
         ConsoleLogging.enableConsoleLogging(options.wantsConsoleLogLevel(), options.getConsoleLoggingPattern());
 
+        ActivityMetrics.setHdrDigits(options.getHdrDigits());
+
         if (options.wantsBasicHelp()) {
             System.out.println(loadHelpFile("basic.md"));
             System.exit(0);

engine-cli/src/main/java/io/nosqlbench/engine/cli/NBCLIOptions.java

@@ -53,6 +53,7 @@ public class NBCLIOptions {
     private static final String WAIT_MILLIS = "waitmillis";
     private static final String EXPORT_CYCLE_LOG = "--export-cycle-log";
     private static final String IMPORT_CYCLE_LOG = "--import-cycle-log";
+    private static final String HDR_DIGITS = "--hdr-digits";
 
     // Execution Options
 
@@ -127,7 +128,7 @@ public class NBCLIOptions {
     private final List<String> wantsToIncludePaths = new ArrayList<>();
     private Scenario.Engine engine = Scenario.Engine.Graalvm;
     private boolean graaljs_compat = false;
-
+    private int hdr_digits = 4;
 
     public NBCLIOptions(String[] args) {
         parse(args);
@@ -213,6 +214,10 @@ public class NBCLIOptions {
                     arglist.removeFirst();
                     logsDirectory = readWordOrThrow(arglist, "a log directory");
                     break;
+                case HDR_DIGITS:
+                    arglist.removeFirst();
+                    hdr_digits = Integer.parseInt(readWordOrThrow(arglist, "significant digits"));
+                    break;
                 case LOGS_MAX:
                     arglist.removeFirst();
                     logsMax = Integer.parseInt(readWordOrThrow(arglist, "max logfiles to keep"));
@@ -531,6 +536,10 @@ public class NBCLIOptions {
 //    }
 
 
+    public int getHdrDigits() {
+        return hdr_digits;
+    }
+
     public String getProgressSpec() {
         ProgressSpec spec = parseProgressSpec(this.progressSpec);// sanity check
         if (spec.indicatorMode == IndicatorMode.console

engine-docs/src/main/resources/docs-for-nb/reference/command_line.md

@@ -153,6 +153,16 @@ created for this name.
 
     --session-name <name>
 
+If you want to control the number of significant digits in all of the HDR metrics, including histograms and timers, then
+you can do so this way:
+
+    --hdr-digits 4
+
+The default is 4 digits, which creates 10000 equisized histogram buckets for every named metric in every reporting
+interval. For longer running test or for test which do not require this level of precision in metrics, you can set this
+down to 3 or 2.
+
+
 Enlist engineblock to stand up your metrics infrastructure using a local docker runtime:
 
     --docker-metrics