58410aee44
Summary: https://github.com/facebook/rocksdb/issues/2559 reports an overflow in AwaitState. nbronson has debugged the issue and presented the fix, which is applied to this patch. Moreover this patch adds more comments to clarify the logic in AwaitState. I tried with both 16 and 64 threads on update benchmark. The fix lowers cpu usage by 1.6 but also lowers the throughput by 1.6 and 2% respectively. Apparently the bug had favored using the spinning more often. Benchmarks: TEST_TMPDIR=/dev/shm/tmpdb time ./db_bench --benchmarks="fillrandom" --threads=16 --num=2000000 TEST_TMPDIR=/dev/shm/tmpdb time ./db_bench --use_existing_db=1 --benchmarks="updaterandom[X3]" --threads=16 --num=2000000 TEST_TMPDIR=/dev/shm/tmpdb time ./db_bench --use_existing_db=1 --benchmarks="updaterandom[X3]" --threads=64 --num=200000 Results $ cat update-16t-bug.txt | tail -4 updaterandom [AVG 3 runs] : 234117 ops/sec; 51.8 MB/sec updaterandom [MEDIAN 3 runs] : 233581 ops/sec; 51.7 MB/sec 3896.42user 1539.12system 6:50.61elapsed 1323%CPU (0avgtext+0avgdata 331308maxresident)k 0inputs+0outputs (0major+1281001minor)pagefaults 0swaps $ cat update-16t-fixed.txt | tail -4 updaterandom [AVG 3 runs] : 230364 ops/sec; 51.0 MB/sec updaterandom [MEDIAN 3 runs] : 226169 ops/sec; 50.0 MB/sec 3865.46user 1568.32system 6:57.63elapsed 1301%CPU (0avgtext+0avgdata 315012maxresident)k 0inputs+0outputs (0major+1342568minor)pagefaults 0swaps $ cat update-64t-bug.txt | tail -4 updaterandom [AVG 3 runs] : 261878 ops/sec; 57.9 MB/sec updaterandom [MEDIAN 3 runs] : 262859 ops/sec; 58.2 MB/sec 926.27user 578.06system 2:27.46elapsed 1020%CPU (0avgtext+0avgdata 475480maxresident)k 0inputs+0outputs (0major+1058728minor)pagefaults 0swaps $ cat update-64t-fixed.txt | tail -4 updaterandom [AVG 3 runs] : 256699 ops/sec; 56.8 MB/sec updaterandom [MEDIAN 3 runs] : 256380 ops/sec; 56.7 MB/sec 933.47user 575.37system 2:30.41elapsed 1003%CPU (0avgtext+0avgdata 482340maxresident)k 0inputs+0outputs (0major+1078557minor)pagefaults 0swaps Closes https://github.com/facebook/rocksdb/pull/2679 Differential Revision: D5553732 Pulled By: maysamyabandeh fbshipit-source-id: 98b72dc3a8e0f22ea29d4f7c7790af10c369c5bb
RocksDB: A Persistent Key-Value Store for Flash and RAM Storage
RocksDB is developed and maintained by Facebook Database Engineering Team. It is built on earlier work on LevelDB by Sanjay Ghemawat (sanjay@google.com) and Jeff Dean (jeff@google.com)
This code is a library that forms the core building block for a fast key value server, especially suited for storing data on flash drives. It has a Log-Structured-Merge-Database (LSM) design with flexible tradeoffs between Write-Amplification-Factor (WAF), Read-Amplification-Factor (RAF) and Space-Amplification-Factor (SAF). It has multi-threaded compactions, making it specially suitable for storing multiple terabytes of data in a single database.
Start with example usage here: https://github.com/facebook/rocksdb/tree/master/examples
See the github wiki for more explanation.
The public interface is in include/. Callers should not include or
rely on the details of any other header files in this package. Those
internal APIs may be changed without warning.
Design discussions are conducted in https://www.facebook.com/groups/rocksdb.dev/