GET Path Experimental Performance Switches

This document records two experimental environment switches on the object GET path. Both default to off, are read once at startup, and exist to support staged performance work — they are not general tuning knobs. Until this document existed they were referenced only by performance harness scripts, which made them look like orphans during dead-code sweeps; they are kept deliberately (rustfs/backlog#1832).

RUSTFS_GET_SEEK_BUFFER_ENABLE

• Type: boolean (true/false), default false.
• Read once at startup in rustfs/src/app/object_usecase.rs.
• When enabled, small GET responses may be served through an in-memory seek buffer, providing seek support without re-reading the object. The seek-buffer code path is unit-test gated; whether the path stays or graduates to default is a post-1.0 maintainer decision — do not remove either the switch or the gated path as dead code.

RUSTFS_GET_OUTPUT_HANDOFF_ATTRIBUTION_ENABLE

• Type: boolean (true/false), default false.
• Read once at startup in rustfs/src/app/object_usecase.rs.
• When enabled, GET responses attribute output-handoff stage timing in the GET stage metrics, at a small per-request bookkeeping cost. Used by the A/B performance runbooks (scripts/run_get_codec_streaming_smoke.sh, scripts/test_get_1mib_abba_stage_metrics.sh) to compare handoff cost between configurations.

Operational guidance

Leave both switches unset in production. Enable them only when following a performance runbook that asks for them, and unset them afterwards — both are startup-latched, so changing a value requires a process restart to take effect.