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Reducing memory allocation from client-side stats #10705

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42 changes: 31 additions & 11 deletions dd-trace-core/src/main/java/datadog/trace/common/metrics/MetricKey.java
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Original file line number Diff line number Diff line change
@@ -1,15 +1,25 @@
package datadog.trace.common.metrics;

import static datadog.trace.bootstrap.instrumentation.api.UTF8BytesString.EMPTY;

import datadog.trace.api.cache.DDCaches;
import datadog.trace.api.cache.DDCache;
import datadog.trace.bootstrap.instrumentation.api.UTF8BytesString;
import datadog.trace.util.HashingUtils;

import java.util.Collections;
import java.util.List;
import java.util.Objects;

/** The aggregation key for tracked metrics. */
public final class MetricKey {
static final DDCache<String, UTF8BytesString> RESOURCE_CACHE = DDCaches.newFixedSizeCache(32);
static final DDCache<String, UTF8BytesString> SERVICE_CACHE = DDCaches.newFixedSizeCache(8);
static final DDCache<String, UTF8BytesString> SERVICE_SOURCE_CACHE = DDCaches.newFixedSizeCache(4);
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@amarziali amarziali Mar 2, 2026

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This should be already filled with UTF8BytesString. It can take values of the instrumentation name (that's should also be UTF8BytesString) so I suggest removing caching for this specific one. 4, is also too small

static final DDCache<String, UTF8BytesString> OPERATION_CACHE = DDCaches.newFixedSizeCache(64);
static final DDCache<String, UTF8BytesString> TYPE_CACHE = DDCaches.newFixedSizeCache(8);
static final DDCache<String, UTF8BytesString> KIND_CACHE = DDCaches.newFixedSizeCache(8);
static final DDCache<String, UTF8BytesString> HTTP_METHOD_CACHE = DDCaches.newFixedSizeCache(8);
static final DDCache<String, UTF8BytesString> HTTP_ENDPOINT_CACHE = DDCaches.newFixedSizeCache(32);
Comment on lines +18 to +21
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@amarziali amarziali Mar 2, 2026

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Would it be possible to widen those a bit? Also, for the http endpoint, I'm wondering if we should just do that caching earlier to make other serialisation benefitting of this (i.e. in EndpointResolver)


private final UTF8BytesString resource;
private final UTF8BytesString service;
private final UTF8BytesString serviceSource;
Expand Down Expand Up @@ -37,19 +47,19 @@ public MetricKey(
List<UTF8BytesString> peerTags,
CharSequence httpMethod,
CharSequence httpEndpoint) {
this.resource = null == resource ? EMPTY : UTF8BytesString.create(resource);
this.service = null == service ? EMPTY : UTF8BytesString.create(service);
this.serviceSource = null == serviceSource ? null : UTF8BytesString.create(serviceSource);
this.operationName = null == operationName ? EMPTY : UTF8BytesString.create(operationName);
this.type = null == type ? EMPTY : UTF8BytesString.create(type);
this.resource = utf8(RESOURCE_CACHE, resource);
this.service = utf8(SERVICE_CACHE, service);
this.serviceSource = utf8(SERVICE_SOURCE_CACHE, serviceSource);
this.operationName = utf8(OPERATION_CACHE, operationName);
this.type = utf8(TYPE_CACHE, type);
this.httpStatusCode = httpStatusCode;
this.synthetics = synthetics;
this.isTraceRoot = isTraceRoot;
this.spanKind = null == spanKind ? EMPTY : UTF8BytesString.create(spanKind);
this.spanKind = utf8(KIND_CACHE, spanKind);
this.peerTags = peerTags == null ? Collections.emptyList() : peerTags;
this.httpMethod = httpMethod == null ? null : UTF8BytesString.create(httpMethod);
this.httpEndpoint = httpEndpoint == null ? null : UTF8BytesString.create(httpEndpoint);

this.httpMethod = utf8(HTTP_METHOD_CACHE, httpMethod);
this.httpEndpoint = utf8(HTTP_ENDPOINT_CACHE, httpEndpoint);
int tmpHash = 0;
tmpHash = HashingUtils.addToHash(tmpHash, this.isTraceRoot);
tmpHash = HashingUtils.addToHash(tmpHash, this.spanKind);
Expand All @@ -65,6 +75,16 @@ public MetricKey(
tmpHash = HashingUtils.addToHash(tmpHash, this.httpMethod);
this.hash = tmpHash;
}

static UTF8BytesString utf8(DDCache<String, UTF8BytesString> cache, CharSequence charSeq) {
if ( charSeq == null ) {
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@amarziali amarziali Mar 2, 2026

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There are things that are supposing to check nullity of this. Now if we replace with empty is not more the same semantic and this will break some code. I suggest to let the caller return the default value so it won't break the existing logic

return UTF8BytesString.EMPTY;
} else if ( charSeq instanceof UTF8BytesString ) {
return (UTF8BytesString)charSeq;
} else {
return cache.computeIfAbsent(charSeq.toString(), UTF8BytesString::create);
}
}

public UTF8BytesString getResource() {
return resource;
Expand Down
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