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Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/14934 First diff in the async read stack: pure plumbing, no behavior change. Both the point `Get` path and the batched `MultiGet` path gain synchronous/coroutine twins generated by `DEFINE_SYNC_AND_ASYNC`; `DB::GetAsync` and `DB::MultiGetAsync` become the public callback-based async entry points with synchronous default implementations. For `Get`, the existing `DBImpl::Get` / `GetImpl` bodies are relocated into the sync/async wrapper. For `MultiGet`, the same wiring continues through the DBImpl, version, and table-cache layers. The generated coroutine variants still run the existing synchronous logic. This keeps the refactor mechanical while preserving dispatch semantics: the coroutine side remains virtual at the same `GetImpl` boundary as the synchronous path, read-only and secondary DBs use generated sync/coroutine overrides instead of falling back to base `DBImpl`, and `StackableDB` leaves async `Get` / `MultiGet` to the base wrappers so wrapper-specific `Get` / `MultiGet` behavior is preserved. For ABI compatibility and avoiding MACRO blocks in public headers, the asynchronous APIs are callback based instead of coroutine based. Internally it will be developed using coroutines, and applications can also develop their own coroutine wrappers. This is meant to make the later changes to actually enable coroutine-backed async queries much easier to review. Benchmarks: Compared `db_bench` with and without this diff using: `db_bench --benchmarks=fillseq,readrandom --num=1000000 --reads=5000000 --key_size=16 --value_size=100 --seed=12345 --db=<tmp>` | Benchmark | Without diff avg | With diff avg | Delta | | `fillseq` | 4.076 us/op | 4.165 us/op | +2.2% | | `readrandom` | 3.939 us/op | 3.947 us/op | +0.2% | No meaningful local `db_bench` regression was observed. Reviewed By: xingbowang Differential Revision: D109346179 fbshipit-source-id: 0dee1239f49099b67c11c63426204466e963f903