LSP Memory Audit

Stage 6 / v1.0 RC readiness review of LSP heap behaviour. Complements the latency + idle-heap benchmarks in Performance Benchmarks.

Audit date: 2026-06-24
Harness: scripts/audit-lsp-memory.mjs
Committed report: benchmarks/lsp-memory-audit.json

Reproduce:

cd superjs && pnpm nx build lsp
cd .. && node --expose-gc scripts/audit-lsp-memory.mjs
# optional heap snapshot for Chrome DevTools:
node --expose-gc scripts/audit-lsp-memory.mjs --snapshot

Summary

Check	Result	Target
Idle heap (~100k LOC corpus, single file)	195.8 MB	≤ 250 MB
`didClose` releases analysis state	186.8 MB freed (ratio 1.0)	≥ 35% release
LRU evicts oldest file under 2 MiB budget	oldest file empty on query	—
Multi-file plateau (5 × ~20k LOC)	45 MB growth	≤ 120 MB

Verdict: No unbounded retention found. Per-file state is released on close and LRU eviction; dominant cost is the in-memory AST + type environment for the active file(s).

What is retained per open document

Source text — LspServer.sources and Compiler.rawSources share the same string reference from textDocument/didOpen (not triple-allocated).
FileState (compiler) — parsed AST, diagnostics, typed spans, lowered IR snapshot, and module export surface. This is the bulk of heap usage (~190 MB for ~140k LOC synthetic corpus vs ~5.3 MB source text).
Touch metadata — URI → LRU tick map (negligible).

Eviction path (enforceBudget or didClose) calls compiler.removeFile, which drops files and rawSources entries for that URI.

Known limitations (post-1.0)

Item	Status
`lsp.memoryBudgetMB` estimates bytes from source length only	Does not account for AST/type overhead; a single huge file can exceed true heap budget while under byte estimate
No `SJS-W010` client diagnostic on heap pressure	Spec'd; not yet emitted (README notes as later work)
JSON-RPC 8 MiB message cap	Planned (threat model T3)
Per-phase memory breakdown	Not instrumented in compiler pipeline

Relation to CI

Bench gate: scripts/check-bench-results.mjs enforces idle heap + P99 hover from benchmarks/results.json.
Audit gate: scripts/check-lsp-memory-audit.mjs enforces close + LRU checks from benchmarks/lsp-memory-audit.json.

Last updated: 2026-06-24.