changes after adx-collector pprof (in prod) for CPU optimization

[Elaa_jamazi (Elaa-jamazi)]

Summary

Optimizes CPU/allocation overhead in Collector, driven by pprof profiling of collector pods in production, which identified excessive per-request allocations in protobuf decode and remote-write handling as a top CPU contributor.

Changes

•  pkg/prompb/protobuf.go ,  pkg/prompb/protobuf_test.go : Reuse  Label / Sample / TimeSeries  objects during protobuf decode instead of allocating fresh ones per request; return  WriteRequest s and dropped series to pools after use.
•  collector/metrics/handler.go ,  collector/metrics/handler_test.go : Wire pooled objects back through the write path so pooled requests are safely reused after a request completes.
•  collector/scraper.go ,  collector/otlp/metrics.go : Adjust the scraper and OTLP ingestion paths to participate correctly in the pooling lifecycle (no double-pooling/use-after-reset).
•  transform/transformer.go ,  transform/transformer_test.go : Preserve reusable label objects when transformations drop labels or series, avoiding unnecessary reallocation.

[Mike Keesey (mkeesey)]

This change unfortunately ignores the comment above that was removed. We should probably create the write requests directly instead of the pool so it's not as confusing, but this can be problematic. WriteRequests contain collections of objects which can contain many many objects, especially after restarts when senders flush a lot of data.

Retaining WriteRequests that have accumulated a lot of data can cause a collector to easily exceed its heap even when we don't need all of that space for subsequent operations later. We'll still be holding onto them within the pool.

[Elaa_jamazi (Elaa-jamazi)]

I addressed this issue. Now requests write request like you recommended: req := &prompb.WriteRequest{}  +  defer req.Reset()  — allocates the outer struct directly (cheap; just slice headers) and still releases its inner  TimeSeries / Label / Sample  objects back to the bounded  TimeSeriesPool  via  Reset()

[Elaa_jamazi (Elaa-jamazi)]

what if we add a boundedpool to avoid a pool causing a lot of memory to be used over time and to avoid the collection of objects concern with the WriteRequests? Each pooled  TimeSeries  is now capped at ~516 KiB (64 labels × 8 KiB max each, plus ~4 KiB of samples, if a Timeseries is oversized it's left for normal Go GC instead ). A new  BoundedPool  caps the pool to at most 1024 retained items via a fixed-capacity channel — anything beyond that is dropped instead of pooled. Multiplying these two hard limits (1024 × 516 KiB ≈ 530 MiB) gives a true worst-case ceiling, not an average, so the pool's memory footprint can never exceed that regardless of traffic burst size.

[Mike Keesey (mkeesey)]

This appears to add several different encoder resets with different lifecycles than we typically do. It also changes quite a lot of the logic in ways that I'm not very sure is safe. This store implementation is pretty heavily tested and benchmarked and deserves a lot of scrutiny.

[Elaa_jamazi (Elaa-jamazi)]

As we discussed on teams, I'll be removing the changes made to the log path, for now

[matucker-msft]

Elaa_jamazi (@Elaa-jamazi) please sign the CLA so we can review this change. Thanks.

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