perf: Encode FDv2 polling payloads in a single jwriter pass - #797
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perf: Encode FDv2 polling payloads in a single jwriter pass#797keelerm84 wants to merge 3 commits into
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keelerm84
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Aug 6, 2026
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- test: Add benchmarks for the FDv2 polling handlers
- perf: Encode FDv2 polling payloads in a single jwriter pass
Whole-handler benchmarks for pollHandlerV2 (/sdk/poll) and pollEvalHandlerV2Shared (/sdk/poll/eval) over a realistic data set (flags with rules and targets, plus segments) at 100 and 2000 flags. These establish the baseline for optimizing the payload serialization, which live traces show dominating /sdk/poll request time.
The FDv2 polling handlers built their response by marshaling every item into its own jwriter buffer, boxing each event into an any-typed struct, and then running encoding/json over the whole document -- which walks it by reflection and re-scans every embedded raw JSON object through its compact() validator before copying it into yet another buffer. Replace that with fdv2PayloadWriter, which writes the entire document in one jwriter pass; put-object bodies are marshaled directly into the output buffer. This is the same treatment the FDv2 SSE events received in the streaming path, and the encoder is pinned to encoding/json's output by equivalence tests (structurally equal; jwriter does not HTML-escape, which the streaming encoders already ship). Benchmarks (2000 flags): /sdk/poll 29.5ms -> 13.3ms per request (-55%) with allocations down from 15046 to 45 (-99.7%); /sdk/poll/eval 1.97ms -> 1.54ms (-22%) with allocations halved, the remainder being evaluation itself. The pollingPayload/payloadEvent types move into test code, where they still describe the wire format that responses are unmarshaled through.
The polling fdv2PayloadWriter and internal/streams' SSE encoders spell out the same protocol event shapes in separate jwriter code. These tests run the same inputs through both and require identical event names and data JSON, so a protocol-shape change in either implementation fails until both move. The streaming encoders' output shapes were otherwise almost unasserted. The comparison also covers the intent payloads: the streams package derives the up-to-date and full-transfer intents from the selector internally, so the payloads the polling handlers construct must match.
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