[Backport 7.79.x] dyninst/symdb: stream JSON into gzip, chunk by compressed size

[dd-octo-sts]

Backport 1f3b62b from #50396.

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What does this PR do?

The SymDB upload pipeline previously held each batch in memory three times over: as a []Scope slice, as a marshalled JSON []byte, and as a gzipped []byte. Batches were flushed by buffered function count (default 10000), which let the in-memory []Scope grow large before any compression.

Replace UploadBatch([]Scope) with a streaming BatchEncoder that owns the gzip writer and a json.Encoder wrapping it. Scopes are encoded straight into the gzip stream as they arrive, the caller no longer accumulates a slice, and flushes are triggered when the compressed buffer reaches a threshold (DefaultFlushThresholdBytes = 2 MiB). The envelope is written inside the gzip stream as {service,version,language,upload_id,batch_num, scopes:[...],final}, with final written at flush time.

Threshold is soft: gzip's internal window means the flushed payload may overshoot by up to ~32 KiB. A threshold <= 0 forces per-scope flushing, preserving the cancel-between-flushes test behaviour previously achieved with maxBufferFuncs=1.

ErrUpload is exposed as a sentinel so callers can distinguish HTTP-side failures (retryable) from local encoder errors via errors.Is.

Motivation

We've seen OOMs uploading symdb data.

Describe how you validated your changes

I've built out a separate benchmarking harness and run it with GC tracing to find the peak heap usage. Before this change on a binary we were failing to upload, the peak heap usage was 52MiB and after it is 20MiB. This represents a 61% reduction in heap memory usage.

Additional Notes

https://datadoghq.atlassian.net/browse/DEBUG-5553

[dd-octo-sts]

Files inventory check summary

File checks results against ancestor cf07a5aa:

Results for datadog-agent_7.79.0~rc.5.git.6.ad3bbc5.pipeline.111830994-1_amd64.deb:

No change detected

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: 823fbf85-a041-4c72-88f4-c6c3297f9a1a

Baseline: cf07a5a
Comparison: ad3bbc5
Diff

Optimization Goals: ✅ No significant changes detected

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	docker_containers_cpu	% cpu utilization	+1.54	[-1.40, +4.47]	1	Logs

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	docker_containers_cpu	% cpu utilization	+1.54	[-1.40, +4.47]	1	Logs
➖	ddot_metrics_sum_cumulative	memory utilization	+0.70	[+0.54, +0.85]	1	Logs
➖	otlp_ingest_logs	memory utilization	+0.63	[+0.52, +0.73]	1	Logs
➖	ddot_metrics	memory utilization	+0.58	[+0.39, +0.76]	1	Logs
➖	quality_gate_metrics_logs	memory utilization	+0.54	[+0.31, +0.78]	1	Logs bounds checks dashboard
➖	ddot_logs	memory utilization	+0.19	[+0.13, +0.25]	1	Logs
➖	quality_gate_idle	memory utilization	+0.17	[+0.12, +0.22]	1	Logs bounds checks dashboard
➖	ddot_metrics_sum_cumulativetodelta_exporter	memory utilization	+0.15	[-0.07, +0.38]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	+0.05	[-0.37, +0.47]	1	Logs
➖	uds_dogstatsd_20mb_12k_contexts_20_senders	memory utilization	+0.04	[-0.02, +0.11]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	+0.02	[-0.09, +0.13]	1	Logs
➖	uds_dogstatsd_to_api_v3	ingress throughput	+0.01	[-0.19, +0.21]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.08, +0.08]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	-0.01	[-0.21, +0.19]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	-0.03	[-0.42, +0.37]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	-0.07	[-0.61, +0.47]	1	Logs
➖	quality_gate_idle_all_features	memory utilization	-0.12	[-0.15, -0.08]	1	Logs bounds checks dashboard
➖	file_tree	memory utilization	-0.27	[-0.33, -0.21]	1	Logs
➖	otlp_ingest_metrics	memory utilization	-0.31	[-0.47, -0.16]	1	Logs
➖	docker_containers_memory	memory utilization	-0.40	[-0.48, -0.32]	1	Logs
➖	ddot_metrics_sum_delta	memory utilization	-0.47	[-0.64, -0.29]	1	Logs
➖	tcp_syslog_to_blackhole	ingress throughput	-0.54	[-0.74, -0.33]	1	Logs
➖	quality_gate_logs	% cpu utilization	-2.37	[-3.94, -0.79]	1	Logs bounds checks dashboard

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	docker_containers_cpu	simple_check_run	10/10	700 ≥ 26
✅	docker_containers_memory	memory_usage	10/10	275.67MiB ≤ 370MiB
✅	docker_containers_memory	simple_check_run	10/10	692 ≥ 26
✅	file_to_blackhole_0ms_latency	memory_usage	10/10	0.19GiB ≤ 1.20GiB
✅	file_to_blackhole_0ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_1000ms_latency	memory_usage	10/10	0.24GiB ≤ 1.20GiB
✅	file_to_blackhole_1000ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_100ms_latency	memory_usage	10/10	0.20GiB ≤ 1.20GiB
✅	file_to_blackhole_100ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_500ms_latency	memory_usage	10/10	0.22GiB ≤ 1.20GiB
✅	file_to_blackhole_500ms_latency	missed_bytes	10/10	0B = 0B
✅	quality_gate_idle	intake_connections	10/10	4 = 4	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	174.99MiB ≤ 181MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	4 = 4	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	495.25MiB ≤ 550MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	209.07MiB ≤ 220MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	354.98 ≤ 2000	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	410.84MiB ≤ 475MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard

Explanation

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

CI Pass/Fail Decision

✅ Passed. All Quality Gates passed.

• quality_gate_metrics_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.