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Merged
paullegranddc merged 6 commits into from
May 7, 2026
Merged

perf(trace-serializer): pre-allocate serialization buffer #1949

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5a2f4c7
perf(trace-serializer): pre-allocate serialization buffer
paullegranddc May 6, 2026
c9f2cc4
fix: make TraceSerializer persistent
paullegranddc May 6, 2026
fff9999
fix: wasm only codepath
paullegranddc May 6, 2026
d74ef62
fix: adress comments
paullegranddc May 7, 2026
ccd7c0c
fix: TraceSerializer import on wasm
paullegranddc May 7, 2026
da0086a
fix: fmt
paullegranddc May 7, 2026
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6 changes: 4 additions & 2 deletions libdd-data-pipeline/src/trace_exporter/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,8 @@ use crate::trace_exporter::TelemetryConfig;
use crate::trace_exporter::TraceExporterWorkers;
use crate::trace_exporter::{
add_path, StatsComputationStatus, TelemetryInstrumentationSessions, TraceExporter,
TraceExporterError, TraceExporterInputFormat, TraceExporterOutputFormat, TracerMetadata,
INFO_ENDPOINT,
TraceExporterError, TraceExporterInputFormat, TraceExporterOutputFormat, TraceSerializer,
TracerMetadata, INFO_ENDPOINT,
};
use arc_swap::ArcSwap;
use libdd_capabilities::{HttpClientTrait, MaybeSend};
Expand Down Expand Up @@ -400,6 +400,7 @@ impl TraceExporterBuilder {
},
input_format: self.input_format,
output_format: self.output_format,
serializer: TraceSerializer::new(self.output_format),
client_computed_top_level: self.client_computed_top_level,
shared_runtime,
dogstatsd,
Expand Down Expand Up @@ -484,6 +485,7 @@ impl TraceExporterBuilder {
},
input_format: self.input_format,
output_format: self.output_format,
serializer: TraceSerializer::new(self.output_format),
client_computed_top_level: self.client_computed_top_level,
shared_runtime,
dogstatsd,
Expand Down
9 changes: 5 additions & 4 deletions libdd-data-pipeline/src/trace_exporter/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -215,6 +215,7 @@ pub struct TraceExporter<H: HttpClientTrait + MaybeSend + Sync + 'static> {
metadata: TracerMetadata,
input_format: TraceExporterInputFormat,
output_format: TraceExporterOutputFormat,
serializer: TraceSerializer,
shared_runtime: Arc<SharedRuntime>,
/// None if dogstatsd is disabled
dogstatsd: Option<Client>,
Expand Down Expand Up @@ -616,11 +617,11 @@ impl<H: HttpClientTrait + MaybeSend + Sync + 'static> TraceExporter<H> {
return self.send_otlp_traces_inner(traces, config).await;
}

let serializer = TraceSerializer::new(
self.output_format,
let prepared = match self.serializer.prepare_traces_payload(
traces,
header_tags,
self.agent_payload_response_version.as_ref(),
);
let prepared = match serializer.prepare_traces_payload(traces, header_tags) {
) {
Ok(p) => p,
Err(e) => {
error!("Error serializing traces: {e}");
Expand Down
97 changes: 58 additions & 39 deletions libdd-data-pipeline/src/trace_exporter/trace_serializer.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,8 @@
// Copyright 2024-Present Datadog, Inc. https://www.datadoghq.com/
// SPDX-License-Identifier: Apache-2.0

use std::sync::atomic::{AtomicUsize, Ordering};

use crate::trace_exporter::agent_response::{
AgentResponsePayloadVersion, DATADOG_RATES_PAYLOAD_VERSION,
};
Expand All @@ -16,6 +18,9 @@ use libdd_trace_utils::span::{v04::Span, TraceData};
use libdd_trace_utils::trace_utils::{self, TracerHeaderTags};
use libdd_trace_utils::tracer_payload;

/// Minimal capacity of fresh buffers allocated to encode traces, in bytes.
const MIN_BUFFER_CAPACITY: usize = 1024;
Comment thread
paullegranddc marked this conversation as resolved.

/// Prepared traces payload ready for sending to the agent
pub(super) struct PreparedTracesPayload {
/// Serialized msgpack payload
Expand All @@ -27,20 +32,18 @@ pub(super) struct PreparedTracesPayload {
}

/// Trace serialization client for handling payload preparation
pub(super) struct TraceSerializer<'a> {
#[derive(Debug)]
pub(super) struct TraceSerializer {
previous_serialised_len: AtomicUsize,
output_format: TraceExporterOutputFormat,
agent_payload_response_version: Option<&'a AgentResponsePayloadVersion>,
}

impl<'a> TraceSerializer<'a> {
impl TraceSerializer {
/// Create a new trace serializer
pub(super) fn new(
output_format: TraceExporterOutputFormat,
agent_payload_response_version: Option<&'a AgentResponsePayloadVersion>,
) -> Self {
pub(super) fn new(output_format: TraceExporterOutputFormat) -> Self {
Self {
previous_serialised_len: AtomicUsize::new(MIN_BUFFER_CAPACITY),
output_format,
agent_payload_response_version,
}
}

Expand All @@ -49,10 +52,12 @@ impl<'a> TraceSerializer<'a> {
&self,
traces: Vec<Vec<Span<T>>>,
header_tags: TracerHeaderTags,
agent_payload_response_version: Option<&AgentResponsePayloadVersion>,
) -> Result<PreparedTracesPayload, TraceExporterError> {
let payload = self.collect_and_process_traces(traces)?;
let chunks = payload.size();
let headers = self.build_traces_headers(header_tags, chunks);
let headers =
self.build_traces_headers(header_tags, chunks, agent_payload_response_version);
let mp_payload = self.serialize_payload(&payload)?;

Ok(PreparedTracesPayload {
Expand All @@ -77,13 +82,18 @@ impl<'a> TraceSerializer<'a> {
}

/// Build HTTP headers for traces request
fn build_traces_headers(&self, header_tags: TracerHeaderTags, chunk_count: usize) -> HeaderMap {
fn build_traces_headers(
&self,
header_tags: TracerHeaderTags,
chunk_count: usize,
agent_payload_response_version: Option<&AgentResponsePayloadVersion>,
) -> HeaderMap {
let mut headers: HeaderMap = header_tags.into();
headers.reserve(4);
headers.insert(DATADOG_SEND_REAL_HTTP_STATUS, HeaderValue::from_static("1"));
headers.insert(DATADOG_TRACE_COUNT, chunk_count.into());
headers.insert(CONTENT_TYPE, APPLICATION_MSGPACK);
if let Some(agent_payload_response_version) = &self.agent_payload_response_version {
if let Some(agent_payload_response_version) = agent_payload_response_version {
// should never fail, as the version should only contain visible ascii chars
let _ = HeaderValue::try_from(agent_payload_response_version.header_value())
.map(|v| headers.insert(DATADOG_RATES_PAYLOAD_VERSION, v));
Expand All @@ -96,12 +106,24 @@ impl<'a> TraceSerializer<'a> {
&self,
payload: &tracer_payload::TraceChunks<T>,
) -> Result<Vec<u8>, TraceExporterError> {
match payload {
tracer_payload::TraceChunks::V04(p) => Ok(msgpack_encoder::v04::to_vec(p)),
let capacity = self
.previous_serialised_len
.load(Ordering::Relaxed)
.max(MIN_BUFFER_CAPACITY);
Comment on lines +109 to +112
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@chatgpt-codex-connector chatgpt-codex-connector Bot May 6, 2026

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P2 Badge Persist the serializer across sends

In the production agent path I checked, send_trace_chunks_inner constructs a fresh TraceSerializer immediately before the single prepare_traces_payload call (libdd-data-pipeline/src/trace_exporter/mod.rs:619-623), so this load always sees the constructor's MIN_BUFFER_CAPACITY value rather than the previous payload size. That means batches larger than 1KB still grow from a 1KB allocation on every send, and the stored length is discarded when the local serializer is dropped; to get the intended pre-allocation, the serializer state needs to live across send calls.

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@yannham yannham May 6, 2026

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If this is true, maybe previous_serialized_len should be a static ? Or would the scope be too large?

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@paullegranddc paullegranddc May 6, 2026

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It is true, I just refactored the TraceSerializer and stored it in the TraceExporter, this way it persists across sends

let buff = match payload {
tracer_payload::TraceChunks::V04(p) => {
msgpack_encoder::v04::to_vec_with_capacity(p, capacity as u32)
}
tracer_payload::TraceChunks::V05(p) => {
rmp_serde::to_vec(p).map_err(TraceExporterError::Serialization)
let mut buff = Vec::with_capacity(capacity);
rmp_serde::encode::write(&mut buff, p)
.map_err(TraceExporterError::Serialization)?;
buff
}
}
};
self.previous_serialised_len
.store(buff.len(), Ordering::Relaxed);
Ok(buff)
}
}

Expand Down Expand Up @@ -146,30 +168,27 @@ mod tests {

#[test]
fn test_trace_serializer_new() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
assert!(matches!(
serializer.output_format,
TraceExporterOutputFormat::V04
));
assert!(serializer.agent_payload_response_version.is_none());
}

#[test]
fn test_trace_serializer_new_with_agent_version() {
let agent_version = AgentResponsePayloadVersion::new();
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05, Some(&agent_version));
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05);
assert!(matches!(
serializer.output_format,
TraceExporterOutputFormat::V05
));
assert!(serializer.agent_payload_response_version.is_some());
}

#[test]
fn test_build_traces_headers() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let header_tags = create_test_header_tags();
let headers = serializer.build_traces_headers(header_tags, 3);
let headers = serializer.build_traces_headers(header_tags, 3, None);

// Check basic headers are present
assert_eq!(headers.get(DATADOG_SEND_REAL_HTTP_STATUS).unwrap(), "1");
Expand Down Expand Up @@ -197,9 +216,9 @@ mod tests {
#[test]
fn test_build_traces_headers_with_agent_version() {
let agent_version = AgentResponsePayloadVersion::new();
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, Some(&agent_version));
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let header_tags = create_test_header_tags();
let headers = serializer.build_traces_headers(header_tags, 2);
let headers = serializer.build_traces_headers(header_tags, 2, Some(&agent_version));

// Check that agent payload version header is included
assert!(headers.contains_key(DATADOG_RATES_PAYLOAD_VERSION));
Expand All @@ -208,7 +227,7 @@ mod tests {

#[test]
fn test_collect_and_process_traces_v04() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let traces = vec![vec![create_test_span()]];

let result = serializer.collect_and_process_traces(traces);
Expand All @@ -221,7 +240,7 @@ mod tests {

#[test]
fn test_collect_and_process_traces_v05() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05);
let traces = vec![vec![create_test_span()]];

let result = serializer.collect_and_process_traces(traces);
Expand All @@ -234,7 +253,7 @@ mod tests {

#[test]
fn test_collect_and_process_traces_multiple_chunks() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let traces = vec![
vec![create_test_span()],
vec![create_test_span(), create_test_span()],
Expand All @@ -250,7 +269,7 @@ mod tests {

#[test]
fn test_serialize_payload_v04() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let original_traces = vec![vec![create_test_span()]];
let payload = serializer
.collect_and_process_traces(original_traces.clone())
Expand Down Expand Up @@ -285,7 +304,7 @@ mod tests {

#[test]
fn test_serialize_payload_v05() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05);
let original_traces = vec![vec![create_test_span()]];
let payload = serializer
.collect_and_process_traces(original_traces.clone())
Expand Down Expand Up @@ -320,14 +339,14 @@ mod tests {

#[test]
fn test_prepare_traces_payload_v04() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let traces = vec![
vec![create_test_span()],
vec![create_test_span(), create_test_span()],
];
let header_tags = create_test_header_tags();

let result = serializer.prepare_traces_payload(traces, header_tags);
let result = serializer.prepare_traces_payload(traces, header_tags, None);
assert!(result.is_ok());

let prepared = result.unwrap();
Expand All @@ -342,11 +361,11 @@ mod tests {

#[test]
fn test_prepare_traces_payload_v05() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V05);
let traces = vec![vec![create_test_span()]];
let header_tags = create_test_header_tags();

let result = serializer.prepare_traces_payload(traces, header_tags);
let result = serializer.prepare_traces_payload(traces, header_tags, None);
assert!(result.is_ok());

let prepared = result.unwrap();
Expand All @@ -358,11 +377,11 @@ mod tests {
#[test]
fn test_prepare_traces_payload_with_agent_version() {
let agent_version = AgentResponsePayloadVersion::new();
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, Some(&agent_version));
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let traces = vec![vec![create_test_span()]];
let header_tags = create_test_header_tags();

let result = serializer.prepare_traces_payload(traces, header_tags);
let result = serializer.prepare_traces_payload(traces, header_tags, Some(&agent_version));
assert!(result.is_ok());

let prepared = result.unwrap();
Expand All @@ -372,11 +391,11 @@ mod tests {

#[test]
fn test_prepare_traces_payload_empty_traces() {
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let traces: Vec<Vec<SpanBytes>> = vec![];
let header_tags = create_test_header_tags();

let result = serializer.prepare_traces_payload(traces, header_tags);
let result = serializer.prepare_traces_payload(traces, header_tags, None);
assert!(result.is_ok());

let prepared = result.unwrap();
Expand All @@ -398,8 +417,8 @@ mod tests {
..Default::default()
};

let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04, None);
let headers = serializer.build_traces_headers(header_tags, 1);
let serializer = TraceSerializer::new(TraceExporterOutputFormat::V04);
let headers = serializer.build_traces_headers(header_tags, 1, None);

assert_eq!(headers.get("datadog-meta-lang").unwrap(), "python");
assert_eq!(headers.get("datadog-meta-lang-version").unwrap(), "3.9.0");
Expand Down
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