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Summary: Fix thread-safety issues in memtable stats tracking and `MaybeUpdateNewestUDT` to prepare for PR https://github.com/facebook/rocksdb/issues/14448, which introduces concurrent range tombstone insertion from the read path into the mutable memtable. Currently the non-concurrent write path updates memtable counters (`num_entries_`, `num_deletes_`, `num_range_deletes_`, `data_size_`) using non-atomic load/store pairs. While this is safe today PR https://github.com/facebook/rocksdb/issues/14448 will make range_tombstone memtable concurrent, but the main write path can still be non-concurrent. This fix ensures stats are tracked correctly. Similarly, `MaybeUpdateNewestUDT` was not thread-safe and was not called in the concurrent write path at all. This PR also fixes the `post_process_info` delete counter which missed `kTypeSingleDeletion` and `kTypeDeletionWithTimestamp`. ## Key changes - Switch non-concurrent counter updates from `LoadRelaxed`/`StoreRelaxed` pairs to `FetchAddRelaxed` to avoid races with concurrent range tombstone inserts (e.g. `AddLogicallyRedundantRangeTombstone` calling `BatchPostProcess`). - Make `MaybeUpdateNewestUDT` thread-safe by replacing `Slice newest_udt_` with `RelaxedAtomic<const char*> newest_udt_data_` and using a CAS loop. The pointed-to memory lives in the arena and remains valid for the memtable's lifetime. - Call `MaybeUpdateNewestUDT` in the concurrent write path (was previously skipped with a TODO). - Fix `post_process_info->num_deletes++` to also count `kTypeSingleDeletion` and `kTypeDeletionWithTimestamp`, matching the non-concurrent path. - Change `GetNewestUDT()` return type from `const Slice&` to `Slice` (returning by value) to avoid dangling reference issues with the new atomic pointer storage. Updated across `MemTable`, `ReadOnlyMemTable`, `MemTableListVersion`, and `WBWIMemTable`. - Remove unused `Slice newest_udt_` member from `WBWIMemTable`. Pull Request resolved: https://github.com/facebook/rocksdb/pull/14506 Test Plan: - Added `ConcurrentWriteMemTableProperties` test in `db_properties_test.cc`: 4 threads writing puts, deletes, and single deletes concurrently, then verifying `rocksdb.num-entries-active-mem-table` and `rocksdb.num-deletes-active-mem-table` properties are correct. Flush with `flush_verify_memtable_count=true` validates integrity. - Added `ConcurrentGetTableNewestUDT` test in `memtable_list_test.cc`: 4 threads concurrently inserting entries with UDTs via `allow_concurrent=true`, verifying the newest UDT is correctly tracked. - Extended `DuplicateSeq` and `ConcurrentMergeWrite` tests in `db_memtable_test.cc` to verify stat counters after `BatchPostProcess`. - Benchmark results show no performance regression (3 runs each, averaged): **Workload 1: fillrandom** (pure Put workload) ``` ./db_bench -benchmarks=fillrandom -seed=1 -compression_type=none -threads=8 -db=<DB> ``` **Workload 2: readrandomwriterandom** (mixed read/write/delete) ``` # Setup: fillrandom,compact to populate DB (single-threaded) ./db_bench -benchmarks=readrandomwriterandom -seed=1 -compression_type=none \ -use_existing_db=1 -readwritepercent=50 -deletepercent=20 -threads=8 -db=<DB> ``` **Workload 3: fillrandom with range tombstones** (puts interleaved with range deletes) ``` ./db_bench -benchmarks=fillrandom -seed=1 -compression_type=none \ -writes_per_range_tombstone=100 -range_tombstone_width=10 \ -max_num_range_tombstones=1000 -threads=8 -db=<DB> ``` ``` | Benchmark | avg ops/s (main) | avg ops/s (feature) | % change | |------------------------------------|-----------------|--------------------:|----------| | fillrandom | 531,986 | 532,099 | +0.02% | | readrandomwriterandom (50r/30w/20d)| 786,400 | 815,143 | +3.65% | | fillrandom (range tombstones) | 541,656 | 531,008 | -1.97% | ``` Reviewed By: xingbowang Differential Revision: D97974456 Pulled By: joshkang97 fbshipit-source-id: ea95f23953fe37771a599aed61ece1a504b12c2e