3/5: Relocate garbage-heavy blob files without SST rewrites (#15307)

[xingbowang]

Summary:
GitHub Issue: #15301

Why the change is required:
FIFO blob GC couples reclamation to blob age and SST compaction. That rewrites SSTs even when stable blob identities make a physical-only replacement possible.

Previous behavior:
Live blobs were relocated only while compacting referring SSTs, and the standalone prototype depended on a custom blob-map container.

New behavior:
When blob indirection and blob garbage collection are enabled, RocksDB selects an eligible garbage-heavy origin, proves its complete live reference set in a pinned visible-key scan, writes a smaller embedded-table carrier, syncs and verifies it, and atomically publishes the new origin route in the MANIFEST without modifying SSTs. Repeated GC can replace a carrier again; eligibility never compares logical bytes containing original user keys with the carrier's different physical representation.

Implementation:
The change adds garbage-ratio candidate scoring, single-origin census collection, embedded carrier construction, source revalidation, serialized MANIFEST publication, route replacement and rollback, scheduling and retry handling, disk-space reservation, listener accounting, recovery validation, incomplete-output quarantine, obsolete-file cleanup, and repeated relocation support. The table builder's exact output size is the authority for whether a replacement reclaims physical bytes.

Safety, compatibility, and limitations:
The path remains default-off and leaves ordinary compaction priority unchanged. It rejects incomplete censuses, compressed blobs, merge-operator bases that cannot be exposed, non-block-based tables, old table formats, TTL files, blob direct write, and remote compaction. A carrier is published only after Finish, Sync, Close, rename, directory sync, source revalidation, and a physical-size check prove it is durable and smaller. Pinned Versions retain superseded carriers until normal obsolete-file processing can remove them.

Validation:
This single-origin boundary compiles independently. Final-stack coverage exercises relocation without SST rewrites, repeated relocation with both small and 8-KiB user keys, recovery and replay, cancellation, concurrent route changes, column-family drop, corruption, resource bounds, obsolete-file handling, and both full test modes.

Differential Revision: D123122449

[meta-codesync]

@xingbowang has exported this pull request. If you are a Meta employee, you can view the originating Diff in D123122449.

[github-actions]

⚠️ clang-tidy: 5 warning(s) on changed lines

Completed in 1503.3s.

Summary by check

Check	Count
bugprone-argument-comment	5
Total	5

Details

db/blob/blob_file_addition_test.cc (4 warning(s))

db/blob/blob_file_addition_test.cc:122:29: warning: argument name 'origin_file_number' in comment does not match parameter name 'value' [bugprone-argument-comment]
db/blob/blob_file_addition_test.cc:123:29: warning: argument name 'carrier_file_size' in comment does not match parameter name 'value' [bugprone-argument-comment]
db/blob/blob_file_addition_test.cc:148:29: warning: argument name 'origin_file_number' in comment does not match parameter name 'value' [bugprone-argument-comment]
db/blob/blob_file_addition_test.cc:149:29: warning: argument name 'carrier_file_size' in comment does not match parameter name 'value' [bugprone-argument-comment]

db/db_impl/db_impl_compaction_flush.cc (1 warning(s))

db/db_impl/db_impl_compaction_flush.cc:460:57: warning: argument name 'sequence' in comment does not match parameter name 's' [bugprone-argument-comment]