feat(pebbleds): opt-in value separation#11385
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Expose pebble's experimental ValueSeparationPolicy so IPFS blocks can be stored in append-only blob files instead of sstables, keeping only keys and small references in the LSM. - new spec options: valueSeparationEnabled, valueSeparationMinimumSize, valueSeparationMaxBlobReferenceDepth, valueSeparationRewriteMinimumAgeSeconds, valueSeparationTargetGarbageRatio; defaults exported as consts - refuses to open when enabled while formatMajorVersion is pinned below FormatValueSeparation (24), because raising the format is irreversible and must stay an explicit user decision - docs/datastores.md documents measured gains, costs, and precautions; fixes two option names that never matched the code (formatVersionMajor, walMinSyncSeconds)
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Exposes pebble's experimental
ValueSeparationPolicyas opt-in pebbleds config: block bytes move into append-only blob files while sstables keep only keys and small records, so even with the whole repo backed by a single pebble instance, CIDs and other small keys end up physically separated from/blocksdata and compactions stop rewriting unchanged block bytes.In local synthetic benchmarks (NVMe, ext4) this made key-only scans (the listing phase of
ipfs repo gcandipfs refs local) 19-58x faster and random 256KiB reads 10-30% faster, at the cost of 15-35% slower non-fsync writes and slower space reclamation after deletes; precautions and details are indocs/datastores.md.@gammazero curious what you think. My inclination is to park this until the policy is no longer under
Experimentalin pebble v2, but it looks promising enough to have ready, as it brings read speed gain at slight cost of writes/deletes, some users may be ok with this tradeoff.TODO