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Summary:
Follow-ups to the lazy wide-column read API (DB::GetEntityLazy / MultiGetEntityLazy). Three related, low-risk changes under one theme; no public API change.
1. Internal read-API cleanup (retires TODO(lazy-blob-resolution-cleanup)). The lazy byte-range work had left a whole/range/force-verify method fan-out on the blob read path: VersionBlobFetcherBase::FetchBlobRange plus a separate FetchBlobForceVerify, and SameFileBlobReader::GetSameFileBlob paired with GetSameFileBlobRange, with the (verify_checksums, force_verify) decision duplicated across branches. This folds them into a single 3-valued BlobVerifyPolicy (kVerifyIfPresent / kVerifyIfNoAmplification / kSkip, added to db/blob/blob_constants.h) derived once at the resolver boundary and threaded down. FetchBlobRange and GetSameFileBlob now take a range descriptor (range_length == kWholeBlobLength means the whole value) plus the policy; FetchBlobForceVerify and the *Range twins are removed. The public LazyColumnReadRequest::force_verify bool is unchanged. The widely-called lower-layer whole-value primitives (BlobFileReader / BlobSource / Version GetBlob) are intentionally left as delegated primitives to bound blast radius; folding those is a later cleanup.
2. Embedded block-cache-tier quirk fix (retires TODO(lazy-blob-resolution-quirks)). ValidateEmbeddedBlobIndex rejected read_tier == kBlockCacheTier before the blob-cache probe, so a same-file (embedded) column already in the blob cache returned Incomplete under kBlockCacheTier -- unlike the separate-file path, which probes the cache first. The up-front rejection moves to the two no-cache paths (ResolveEmbeddedBlob / ResolveEmbeddedBlobPinned); the cache-probing paths now serve a cached record under kBlockCacheTier, matching separate-file behavior. This is a shared lower-layer change: the non-lazy Get / GetEntity and iterator embedded read paths (get_context / MaybeResolveEmbeddedValue -> ResolveEmbeddedBlobCached) get the same corrected behavior, not just the lazy resolver.
3. Coverage. db_bench gains a readrandomentitylazy benchmark (GetEntityLazy + MultiResolve of --lazy_entity_read_length bytes per column) for measuring byte-range (partial) blob read savings; it requires open_files == -1. The crash test now also fuzzes LazyColumnReadRequest::force_verify in the lazy-vs-eager differential (force_verify affects only verification, not the returned bytes, so the comparison is unchanged).
This also sets up the next planned step -- cross-key coalescing for MultiGetEntityLazy / LazyWideColumnsBatch::MultiResolve. The internal BlobReadRequest already carries a {offset, len} range descriptor, and with the verify decision now a single BlobVerifyPolicy rather than a bool plus a separate force-verify method, a batched resolve can group a vector of range+policy requests per (CF, Version, blob file) and coalesce them onto the existing MultiGetBlob machinery -- without re-introducing whole/range/force-verify method twins in the multi-read path.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/15115
Test Plan:
- New unit test DBLazyEntityTest.EmbeddedBlockCacheTierServedFromCachedValue: a cached embedded column serves whole- and sub-range reads under kBlockCacheTier instead of returning Incomplete. Existing force_verify / BlockCacheTier tests are unchanged (public behavior preserved).
- New unit test DBBlobIndexTest.EmbeddedBlobWideColumnGetEntityBlockCacheTierServesCached: covers the non-lazy GetEntity path -- a cached embedded column is served under kBlockCacheTier; the existing ...GetEntityBlockCacheTier test still asserts a genuine miss yields Incomplete.
- Crash test: extended the existing lazy differential to fuzz force_verify (reuses --lazy_entity_read_one_in).
- db_bench: readrandomentitylazy over 2000 entities x 2 uncompressed embedded blob columns (4000 B each), reading 100 B per column:
| metric | value |
|---|---|
| rocksdb.blobdb.lazy.partial.read.count | 4000 |
| rocksdb.blobdb.lazy.read.bytes | 400000 |
| rocksdb.blobdb.lazy.partial.bytes.saved | 15600000 |
i.e. 100 B read per column instead of the 4000 B whole-column value.
Reviewed By: xingbowang
Differential Revision: D116334969
Pulled By: pdillinger
fbshipit-source-id: cebe90456b23be0f5be60cdc4bff85c8a37b5442