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81ea677072
Summary:
Wide-column read paths that materialize blob-referenced columns used to re-serialize the entire entity into a fresh contiguous buffer, copying the (potentially large) resolved column values byte-for-byte. This was forced by PinnableWideColumns holding a single backing buffer with all column Slices pointing into it.
PinnableWideColumns now holds its columns as zero-copy Slices into one or more stable backing buffers, kept in a std::forward_list<PinnableSlice> whose nodes never relocate on move, move-assignment, or splice. Resolved blob columns can be spliced in as additional backing buffers instead of re-serializing the entity.
Using address-stable nodes also cleans up the old Slice-invalidation handling. The previous single-buffer representation had to cope with a self-pinned PinnableSlice whose small (SSO) std::string relocates when the PinnableSlice is moved: on every move it detected the relocated backing pointer and re-derived the column Slices by re-parsing. With forward_list nodes that never move, the column Slices stay valid across move / move-assignment / splice, so that handling is gone and the move operations are now the defaulted member-wise moves.
The multi-buffer plumbing is internal only: a new PinnableWideColumnsHelper (a friend) performs the splice and the little bit of private-member access the read paths need, so there is no new public API surface and the previous `friend class DBImpl` is gone. The public view is unchanged: columns() still returns a single, in-order set.
Read paths converted to resolve without re-serializing:
- GetContext::SaveWideColumnEntityToColumns (eager GetEntity SST reads, separate-blob-file references)
- DBImpl::ResolveDirectWriteWideColumns (direct-write blob references)
- DBImpl::MaybeResolveMemtableBlobValue (blob-backed memtable reads)
Merge output still serializes (the MergeOperator API consumes/produces a serialized entity). Same-file ("embedded") blob columns are resolved -- and still re-serialized -- earlier in the block-based table reader (MaybeResolveEmbeddedValue / ResolveEmbeddedValueForGet) before the entity reaches GetContext, so the GetEntity path above only avoids re-serialization for separate-blob-file references. Compaction's separate entity machinery is unchanged.
API/accounting: deprecated PinnableWideColumns::serialized_size() (comment-only, per repo convention) in favor of the new payload_size() (sum of column name + value sizes; equals the value size for a plain value). Read statistics for entities (BYTES_READ, BYTES_PER_READ, per-key GetEntity/MultiGetEntity byte counts) and the ReadOptions::value_size_soft_limit threshold now measure entities by payload_size() instead of the serialized size. This drops framing bytes (entity measurements are slightly smaller), thus making plain-value and wide-column accounting consistent and reducing unnecessary exposure to implementation details.
Serialization cleanup enabled by the above:
- Consolidated Deserialize/DeserializeV2 into a single Deserialize(const Slice&, WideColumns&, blob_columns*) plus a DeserializeSimple alias for the no-blob-references case; both take const Slice&, require the input to be exactly one serialized entity, and reject any trailing data uniformly (V1 previously ignored trailing bytes). An unexpected blob reference where a fully-resolved entity is required now returns Corruption.
- ResolveEntityBlobColumns (serialized output, used only by merge) is now a thin wrapper over the new multi-buffer resolver plus Serialize, removing the duplicated fetch loop and the SerializeResolvedEntity helper.
- Consistently use `const Slice& input` rather than `Slice& input` for wide column functions expecting an input slice with no trailing data.
Design/polish from human review:
* The initial plan called for more complex handling around a vector<PinnableSlice> backing store (unique_ptr indirection and re-deriving the column Slices on move to cope with reallocation and SSO relocation); switching the backing store to a std::forward_list of address-stable nodes was a human suggestion that removed that complexity and the move-time Slice re-derivation entirely.
* Keep resolve plumbing off the public API via PinnableWideColumnsHelper and removing the DBImpl friend
* Various pieces of cleanup and polish (more left to do)
* The eager-GetEntity optimization
* The memtable inline-copy NOTE/TODO.
Intended follow-up:
* Resolve FIXME about pre-existing swallowed non-OK status in db_impl.cc
* Resolve TODO about value_size_soft_limit in db_impl.cc
* Extend this optimization to SST embedded-blob references
* Error-status/API cleanup: classify an unrecognized wide-column version as Corruption (not NotSupported) at all entry points; replace the NotSupported sentinel from GetValueOfDefaultColumn with an explicit is_blob_reference out-param (removing GetValueOfDefaultColumnResolvingBlobs); and centralize the "blob-backed value without a blob fetcher" Corruption into the resolvers (resolving the ResolveEntityForMerge FIXME) rather than repeating it at each caller
Pull Request resolved: https://github.com/facebook/rocksdb/pull/14943
Test Plan:
Extended db/wide/wide_column_serialization_test.cc with PinnableWideColumns unit tests: set/payload_size for plain, V1, and resolved entities; move and move-assign of a multi-buffer result preserve column data pointers (the node-stability guarantee); Reset; ResolveColumns splices blob buffers in zero-copy (resolved values' data() point into the spliced-in buffers, not a re-serialized entity); serialized_size() == SerializedSizeV1(columns()); and Deserialize rejects trailing data after a serialized entity for both V1 and V2 layouts.
Built and ran (debug): wide_column_serialization_test, db_wide_basic_test, db_wide_blob_direct_write_test, db_blob_basic_test, compaction_iterator_test, db_merge_operator_test, db_iterator_test, udt_util_test, write_batch_with_index_test -- all pass. librocksdb and db_stress build. make format-auto and build_tools/check-sources.sh are clean.
Reviewed By: xingbowang
Differential Revision: D112212266
Pulled By: pdillinger
fbshipit-source-id: 13b89e2bb7d8371f4c1ff18b234a549bea9c9e77