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rendezvous: stream registry snapshot to disk (drop full-size save buffer) - #130
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flushSave previously encoded the full registry snapshot into a pooled in-memory bytes.Buffer, hashed it, spliced the checksum in, then handed the whole buffer to AtomicWrite for a second full copy. At fleet scale (~250k nodes / 8.3M trust pairs / ~191MB JSON) that buffer dominated the heap and drove GC pauses during saves. Stream the encode straight to the temp file: json.Encoder writes through a MultiWriter(file, sha256); a small trimTrailingNewlineWriter withholds the encoder's trailing newline so the hash matches load()'s newline-stripped recompute; the checksum is backfilled as a trailing JSON member via WriteAt. On-disk format, checksum semantics, and crash recovery (snapshot + WAL replay) are unchanged. Removes flushSaveBufPool and maxPooledSaveBuf. Verified on the live v0.2.6 base: identical snapshot bytes/checksum, crash-restart restores trust pairs from the snapshot, first save ~19s vs ~21s before. Does NOT change save cadence (5s tick and full-snapshot frequency are unchanged).
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| return err | ||
| } | ||
| if err := fn(f); err != nil { | ||
| f.Close() |
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What
flushSaveused to encode the full registry snapshot into a pooled in-memorybytes.Buffer, hash it, splice in the checksum, then hand the entire buffer toAtomicWrite(a second full copy). At fleet scale — ~250k nodes / 8.3M trust pairs / ~191 MB JSON — that buffer dominated the heap and drove GC pauses during saves.This streams the encode directly to the temp file:
json.Encoderwrites through anio.MultiWriter(file, sha256).trimTrailingNewlineWriterwithholds the encoder's trailing\nso the hash covers exactly the bytesload()recomputes (it strips the newline too).WriteAt), preserving the on-disk format.atomicWriteStreamperforms the temp-file → fsync → rename → dir-fsync protocol (same durability asfsutil.AtomicWrite).Removes
flushSaveBufPool/maxPooledSaveBuf.No change to save cadence — 5 s tick and full-snapshot frequency are untouched. This is a memory/CPU optimization only.
Parity
go test ./...across the module is green.Verification (docker, amd64, against the live v0.2.6 base)
Pounded with a local load generator (register + signed heartbeat + signed trust):
v0.2.6 + this patch(no cadence change), deployed topilot-rendezvous-new; 252k nodes preserved, 0 save failures, 0 errors, overlay (directory) green; first post-load save ~19 s vs ~21 s before.Not included (follow-up)
A checkpoint-cadence reduction (snapshot less often; rely on the WAL between) was prototyped and deliberately dropped: the load test showed the WAL only logs
Register/Deregister/Network*/KeyRotation, so trust/hostname/tags/visibility are snapshot-only — lengthening the interval would lose them on crash. That needs the WAL to cover all persistent mutations first.