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volume server: split get_or_head_handler_inner into phases (#11489)
* volume server: read GET/HEAD needles off the store lock, and only once The GET/HEAD handler read the needle synchronously on the tokio worker while holding store.read(): first a stream-info read that loaded the whole record just to parse its meta, then, for every needle that was not streamed (small, compressed, chunk manifest, image ops), a second full read. For a tiered volume each read is an S3 GET under the store lock, and a writer queued behind it parks every other store reader. The regular-volume read now runs in spawn_blocking. Under the store guard it only resolves a NeedleReadPlan (index lookup, a freshly opened .dat handle or the remote backend, offset, size); the guard is dropped before any needle data I/O. No data-file lease is held across the read either, since a writer waits for one while holding the store write lock. The index size decides the read, as in Go's readNeedle: a HEAD, a ranged read or a needle above the stream threshold reads only its header and meta tail (ReadNeedleMeta) and hands off to StreamingBody or the range path; everything else is read in full once, with its checksum verified. A compressed or manifest needle found by the meta read is then read in full once. The range-from-source read also moves to spawn_blocking. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> * volume server: stream needle chunks without the store lock StreamingBody::poll_frame took store.read() and find_volume for every chunk to compare the volume's compaction revision, dup'd the source handle, and allocated a fresh chunk buffer. With -hasSlowRead=false the stream also holds a data-file read lease for its whole life, while a writer waits for that lease under store.write(): the next chunk's store.read() then waits for the writer and the writer for the stream. The per-chunk re-lookup was also wrong. The stream reads a handle opened at plan time, which pins the .dat inode the offset was resolved against; a vacuum commit renames a new file over .dat and leaves that inode untouched. The re-looked-up offset belongs to the new file but was read from the old inode, so a stream whose needle a vacuum moved ended in a checksum error. The pinned offset stays valid, so the check, and with it every store access, is dropped, along with the now unused re_lookup_needle_data_offset and the revision fields of the read plan. The source is shared as an Arc instead of dup'd per chunk, and the chunk buffer is a BytesMut that the blocking read hands back with its result, so its allocation is reclaimed once the previous frame has been written. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> * volume server: split get_or_head_handler_inner into phases get_or_head_handler_inner was a ~650-line function. Its middle resolved the needle and set five mutable flags (stream_info, can_stream, can_handle_head_from_meta, can_handle_range_from_source, bypass_cm) that three if-let reply paths then re-tested, each re-checking stream_info. It is now a 126-line orchestrator over named phases: reject_read_jwt, proxy_missing_volume, wait_for_download_slot, parse_read_request, read_ec_needle / read_volume_needle, etag_and_last_modified, not_modified_response, read_response_headers, and the reply phases stream_response, head_from_meta_response, range_from_source_response, buffered_payload and buffered_response. The read phases return a ReadPlan whose ReadStrategy enum (Stream, HeadFromMeta, RangeFromSource, Buffered) carries the NeedleStreamInfo only on the variants that use it, so the reply is one match instead of three flag checks. Pure refactor: every status code, header and header order, error text, metric increment, lock and data-file lease scope, spawn_blocking boundary and side-effect order is unchanged. Phases that can end the request return ControlFlow<Response, T>. A Range header that is not visible ASCII still falls through to the buffered path, as before. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> * volume server: stop a needle stream once its volume becomes unavailable Taking the store lock out of StreamingBody also dropped its per-chunk unavailable_error() check. With -hasSlowRead a writer can take the data-file lease between chunks, fail its fsync and its truncate, and mark the volume unavailable; the stream then kept serving the rest of the needle from its pinned handle. The volume's io_unavailable reason is now an Arc-shared leaf mutex that the read plan hands to the stream. Each chunk checks it under its data-file lease, where the writer marks it, and fails with the same "volume is unavailable: <reason>" error the old check returned. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> * volume server: mirror Go order in the buffered read path - check HEAD before Range in buffered_response (writeResponseContent order); an EC-volume HEAD with a Range header answered 206, Go answers 200 - treat the proxied flag as an exact query pair like Go's parsed lookup, not a substring - name the phases after their Go counterparts: check_download_limit and read_ec_shard_needle; reuse has_replication() - drop comments that restate the code or cite Go line numbers --------- Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com> Co-authored-by: Chris Lu <chris.lu@gmail.com>
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