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Cache Tracer Host Entry to reduce allocation in RemoteHostnameAdder #10968

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Cache Tracer Host Entry to reduce allocation in RemoteHostnameAdder #10968

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Caching host entry to reduce allocation
dougqh Mar 25, 2026
29f5205
spotless
dougqh Mar 25, 2026
d8d553e
Merge branch 'master' into dougqh/cache-tracer-host
dougqh Mar 27, 2026
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22 changes: 20 additions & 2 deletions dd-trace-core/src/main/java/datadog/trace/core/tagprocessor/RemoteHostnameAdder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,15 +10,33 @@
public final class RemoteHostnameAdder extends TagsPostProcessor {
private final Supplier<String> hostnameSupplier;

private TagMap.Entry cachedHostEntry = null;

public RemoteHostnameAdder(Supplier<String> hostnameSupplier) {
this.hostnameSupplier = hostnameSupplier;
}

@Override
public void processTags(
TagMap unsafeTags, DDSpanContext spanContext, List<AgentSpanLink> spanLinks) {
if (spanContext.getSpanId() == spanContext.getRootSpanId()) {
unsafeTags.put(DDTags.TRACER_HOST, hostnameSupplier.get());
if (spanContext.getSpanId() != spanContext.getRootSpanId()) {
return;
}

String hostname = hostnameSupplier.get();
if (hostname == null) {
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@dougqh dougqh Mar 25, 2026

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This is subtle change in behavior from before.
TagMap.put would have failed with an exception when given null.

I've decided to just ignore hostnameSupplier.get returning null instead.

return;
}

TagMap.Entry cachedHostEntry = this.cachedHostEntry;

if (cachedHostEntry != null && cachedHostEntry.objectValue().equals(hostname)) {
unsafeTags.set(cachedHostEntry);
return;
}

TagMap.Entry newEntry = TagMap.Entry.create(DDTags.TRACER_HOST, hostname);
unsafeTags.set(newEntry);
this.cachedHostEntry = newEntry;
}
}
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