Truncate gen_ai attributes to 256KB instead of exempting from truncation#48454
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Truncate gen_ai attributes to 256KB instead of exempting from truncation#48454
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Co-authored-by: harsimar <19897860+harsimar@users.noreply.github.com>
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harsimar
March 17, 2026 21:36
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rajkumar-rangaraj,
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Pull request overview
This PR updates Azure Monitor OTel autoconfigure telemetry property truncation behavior so that gen_ai.* custom dimensions are no longer fully exempt from truncation, but instead use a higher truncation threshold (256 * 1024) compared to the default 8192.
Changes:
- Introduced a higher max value length for a defined set of
gen_ai.*property keys and routed them through the truncation helper using that higher limit. - Updated unit tests to validate
gen_ai.*properties truncate at the higher limit and remain unmodified below it.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
sdk/monitor/azure-monitor-opentelemetry-autoconfigure/src/main/java/com/azure/monitor/opentelemetry/autoconfigure/implementation/builders/AbstractTelemetryBuilder.java |
Adds a higher truncation limit for specific gen_ai.* keys and applies TelemetryTruncation.truncatePropertyValue with that limit. |
sdk/monitor/azure-monitor-opentelemetry-autoconfigure/src/test/java/com/azure/monitor/opentelemetry/autoconfigure/implementation/builders/AbstractTelemetryBuilderTest.java |
Replaces the prior “not truncated” test with parameterized tests covering truncation at the new threshold and preservation below it. |
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| private static final int MAX_GENAI_PROPERTY_VALUE_LENGTH = 256 * 1024; // 256 KB | ||
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| // gen_ai properties can contain large payloads (e.g. full conversation messages, | ||
| // tool definitions) that should not be truncated | ||
| private static final Set<String> TRUNCATION_EXEMPT_PROPERTY_KEYS = new HashSet<>(asList("gen_ai.input.messages", | ||
| // tool definitions) that are truncated at a higher limit (256 KB) | ||
| private static final Set<String> GENAI_PROPERTY_KEYS = new HashSet<>(asList("gen_ai.input.messages", |
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| if (GENAI_PROPERTY_KEYS.contains(key)) { | ||
| getProperties().put(key, | ||
| TelemetryTruncation.truncatePropertyValue(value, MAX_GENAI_PROPERTY_VALUE_LENGTH, key)); | ||
| } else { | ||
| getProperties().put(key, TelemetryTruncation.truncatePropertyValue(value, MAX_PROPERTY_VALUE_LENGTH, key)); |
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| int size256KB = 256 * 1024; | ||
| String longValue = repeat("a", size256KB + 10000); | ||
| builder.addProperty(key, longValue); | ||
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| TelemetryItem item = builder.build(); | ||
| Map<String, String> properties = getProperties(item); | ||
| assertEquals(size256KB, properties.get(key).length()); |
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Follow-up to #48385. Instead of fully exempting gen_ai custom dimensions from truncation, truncate them at 256KB.
Changes
AbstractTelemetryBuilder: ReplaceTRUNCATION_EXEMPT_PROPERTY_KEYSwithGENAI_PROPERTY_KEYSand addMAX_GENAI_PROPERTY_VALUE_LENGTH = 256 * 1024. Gen_ai keys now route throughTelemetryTruncation.truncatePropertyValuewith the higher limit rather than bypassing truncation entirely.AbstractTelemetryBuilderTest: ReplacegenAiPropertyIsNotTruncatedwith two parameterized tests —genAiPropertyIsTruncatedAt256KB(verifies truncation above limit) andgenAiPropertyUnder256KBIsNotTruncated(verifies preservation below limit).