don't recompute hash for known tags

DataDog · Jul 11, 2024 · 8c523ac · 8c523ac
1 parent 8b00e3e
commit 8c523ac
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Showing 2 changed files with 39 additions and 27 deletions.
diff --git a/dd-trace-core/src/main/java/datadog/trace/core/datastreams/DefaultPathwayContext.java b/dd-trace-core/src/main/java/datadog/trace/core/datastreams/DefaultPathwayContext.java
@@ -33,7 +33,7 @@
 public class DefaultPathwayContext implements PathwayContext {
   private static final Logger log = LoggerFactory.getLogger(DefaultPathwayContext.class);
   private final Lock lock = new ReentrantLock();
-  private final WellKnownTags wellKnownTags;
+  private final long hashOfKnownTags;
   private final TimeSource timeSource;
   private final GrowingByteArrayOutput outputBuffer =
       GrowingByteArrayOutput.withInitialCapacity(20);
@@ -67,7 +67,7 @@ public class DefaultPathwayContext implements PathwayContext {
 
   public DefaultPathwayContext(TimeSource timeSource, WellKnownTags wellKnownTags) {
     this.timeSource = timeSource;
-    this.wellKnownTags = wellKnownTags;
+    this.hashOfKnownTags = PathwayHashBuilder.getBaseHash(wellKnownTags);
   }
 
   private DefaultPathwayContext(
@@ -77,8 +77,7 @@ private DefaultPathwayContext(
       long pathwayStartNanoTicks,
       long edgeStartNanoTicks,
       long hash) {
-    this.timeSource = timeSource;
-    this.wellKnownTags = wellKnownTags;
+    this(timeSource, wellKnownTags);
     this.pathwayStartNanos = pathwayStartNanos;
     this.pathwayStartNanoTicks = pathwayStartNanoTicks;
     this.edgeStartNanoTicks = edgeStartNanoTicks;
@@ -124,7 +123,7 @@ public void setCheckpoint(
       // So far, each tag key has only one tag value, so we're initializing the capacity to match
       // the number of tag keys for now. We should revisit this later if it's no longer the case.
       List<String> allTags = new ArrayList<>(sortedTags.size());
-      PathwayHashBuilder pathwayHashBuilder = new PathwayHashBuilder(wellKnownTags);
+      PathwayHashBuilder pathwayHashBuilder = new PathwayHashBuilder(hashOfKnownTags);
       DataSetHashBuilder dataSetHashBuilder = new DataSetHashBuilder();
 
       if (!started) {
@@ -408,35 +407,35 @@ public long addValue(String val) {
   }
 
   private static class PathwayHashBuilder {
-    private final StringBuilder builder;
+    private long hash;
+
+    public PathwayHashBuilder(long baseHash) {
+      hash = baseHash;
+    }
+
+    public void addTag(String tag) {
+      hash = FNV64Hash.continueHash(hash, tag, FNV64Hash.Version.v1);
+    }
+
+    public long getHash() {
+      return hash;
+    }
 
-    public PathwayHashBuilder(WellKnownTags wellKnownTags) {
-      builder = new StringBuilder();
+    public static long getBaseHash(WellKnownTags wellKnownTags) {
+      StringBuilder builder = new StringBuilder();
       builder.append(wellKnownTags.getService());
       builder.append(wellKnownTags.getEnv());
 
       String primaryTag = Config.get().getPrimaryTag();
       if (primaryTag != null) {
         builder.append(primaryTag);
       }
-    }
-
-    public void addTag(String tag) {
-      builder.append(tag);
-    }
-
-    public long generateHash() {
       return FNV64Hash.generateHash(builder.toString(), FNV64Hash.Version.v1);
     }
-
-    @Override
-    public String toString() {
-      return builder.toString();
-    }
   }
 
   private long generateNodeHash(PathwayHashBuilder pathwayHashBuilder) {
-    return pathwayHashBuilder.generateHash();
+    return pathwayHashBuilder.getHash();
   }
 
   private long generatePathwayHash(long nodeHash, long parentHash) {

diff --git a/internal-api/src/main/java/datadog/trace/util/FNV64Hash.java b/internal-api/src/main/java/datadog/trace/util/FNV64Hash.java
@@ -18,20 +18,33 @@ public static long generateHash(String data, Version version) {
     return generateHash(data.getBytes(), version);
   }
 
+  public static long continueHash(long currentHash, String data, Version version) {
+    return generateHash(currentHash, data.getBytes(), version);
+  }
+
   public static long generateHash(byte[] data, Version version) {
     return generateHash(data, 0, data.length, version);
   }
 
+  public static long generateHash(long currentHash, byte[] data, Version version) {
+    return generateHash(currentHash, data, 0, data.length, version);
+  }
+
   public static long generateHash(byte[] data, int start, int length, Version version) {
+    return generateHash(FNV_INIT, data, start, length, version);
+  }
+
+  public static long generateHash(
+      long currentHash, byte[] data, int start, int length, Version version) {
     if (version == Version.v1) {
-      return generateFNV1Hash(data, start, length);
+      return generateFNV1Hash(currentHash, data, start, length);
     } else {
-      return generateFNV1AHash(data, start, length);
+      return generateFNV1AHash(currentHash, data, start, length);
     }
   }
 
-  private static long generateFNV1Hash(byte[] data, int start, int length) {
-    long hash = FNV_INIT;
+  private static long generateFNV1Hash(long currentHash, byte[] data, int start, int length) {
+    long hash = currentHash;
 
     for (int i = start; i < start + length; i++) {
       hash *= FNV_PRIME;
@@ -41,8 +54,8 @@ private static long generateFNV1Hash(byte[] data, int start, int length) {
     return hash;
   }
 
-  private static long generateFNV1AHash(byte[] data, int start, int length) {
-    long hash = FNV_INIT;
+  private static long generateFNV1AHash(long currentHash, byte[] data, int start, int length) {
+    long hash = currentHash;
 
     for (int i = start; i < start + length; i++) {
       hash ^= 0xffL & data[i];