Summary:
Add stats to monitor the large transaction optimization. A stat is added for how many times wbwi ingestion is used. A histogram is added to track transaction size. We could also just track write batch size for all writes but I don't want to add the overhead to all writes yet.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/13611
Test Plan:
ran `python3 ./tools/db_crashtest.py --txn blackbox --txn_write_policy=0 --commit_bypass_memtable_one_in=50 --test_batches_snapshots=0 --stats_dump_period_sec=2 --dump_malloc_stats=0 --statistics=1` and manually check LOG files
```
rocksdb.number.wbwi.ingest COUNT : 57
...
rocksdb.num.op.per.transaction P50 : 1.000000 P95 : 1.000000 P99 : 1.000000 P100 : 1.000000 COUNT : 2265 SUM : 2265
```
Reviewed By: jowlyzhang
Differential Revision: D74829087
Pulled By: cbi42
fbshipit-source-id: 5a9c3ab2d4cb6071cedfc47201ce2cf65a77d3c6
b42bf48310