perf(cache): parallelize tiered heal reads from the source tier#388
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worstell wants to merge 1 commit into
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perf(cache): parallelize tiered heal reads from the source tier#388worstell wants to merge 1 commit into
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The tier-0 heal previously pulled the whole object from the source tier as a single stream, so only an S3 source (which fans out internally) saturated the link. The heal now drives client.ParallelGetReader itself, pinned to the healed revision via If-Match, giving any Range-capable source tier parallel throughput and degrading to a single stream for sources without Range/ETag support. Heal chunks stay below the S3 tier's internal large-range fan-out threshold so requests are never amplified twice.
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The tier-0 heal (
backfillTier0FromSource) pulled the whole object from the source tier as a single stream, so parallel throughput depended on the source: S3 fans out internally, but any other tier (e.g. a future remote HTTP tier) would be limited to one connection.The heal now uses
client.ParallelGetReaderagainst the source tier directly, with every request pinned to the healed revision via If-Match so a concurrent rewrite fails the heal instead of splicing revisions. Discovery degrades to a single stream when the source lacks Range or ETag support, so non-range-capable sources behave as before.Heal chunks are sized at
minRangePartSize(4 MiB), below the S3 tier's internal large-range fan-out threshold, so each chunk maps to exactly one upstream request and fan-out is never applied twice.Follow-ups (separate PRs): generalize the S3 byte-window adapter over any
Cache, and apply the large-range fan-out policy on theRemote/Tieredranged-read path.