A cached rewrite made with cooldown on stays right until a version it held
back leaves cooldown, so it now expires then instead of after a fixed
time. Handlers ask cooldown through Proxy.cooldown, which reports each
withheld version to the rewrites running at that moment. A rewrite that
held nothing back is kept for the shortest cooldown, at most a day.
pnpm 12 checks every lockfile entry against the registry on each install
unless trustLockfile is set, so each install reads the packument of every
package in the lockfile. The rewrite cache kept each document twice, plain
and gzipped, and with cooldown on for a minute only, so these packuments
were rewritten and compressed again on every install.
Keep only the gzip copy of a cached rewrite, about an eighth of the
document, and decompress it for clients and handlers that need the plain
bytes. Keep rewrites made with cooldown on for an hour. Answer HEAD for
packuments, which pnpm 12 sends before each GET.
With cooldown on, every npm, Composer and Chef metadata request rewrote
the whole document, because a cached rewrite could keep hiding a
version after its cooldown ended. For a 24.5 MB packument that is about
45 ms and 31 MB of allocations per request, and the result was served
uncompressed and without Last-Modified, so Composer, which revalidates
p2 files with If-Modified-Since only, never got a 304.
The rewrite cache now keeps cooldown rewrites with an expiry of one
minute, so a version leaving cooldown shows up at most that late.
Concurrent requests share one rewrite, clients get the gzip copy, and
the rewrite is dated through metadataDate like any other. Its ETag is
the hash of its output, so replicas agree on it.
The cache is keyed by the digest the metadata cache already recorded,
instead of hashing the document again, which also lets storedRewrite
serve cooldown rewrites without reading the stored document.
Without the rewrite cache, cooldown rewrites behave as before.
- Keep a gzip copy of each rewrite cache entry when it is smaller, made once
per rewrite and counted against metadata_rewrite_cache_size
- Serve it with Content-Encoding: gzip to clients that accept gzip, with an
ETag of its own ("<sha256>-gzip") and Vary: Accept-Encoding
- Rewrites made outside the cache (cache disabled, cooldown on) stay
uncompressed
- rewriteCache.get and rewrite return rewrittenMetadata
