From 6ec2bf3fcea3d5c224ad3f82eb87b4ffb86ee490 Mon Sep 17 00:00:00 2001 From: Maysam Yabandeh Date: Thu, 15 Aug 2019 14:39:47 -0700 Subject: [PATCH] Blog post for write_unprepared (#5711) Summary: Introducing write_unprepared feature. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5711 Differential Revision: D16838307 Pulled By: maysamyabandeh fbshipit-source-id: d9a4daf63dd0f855bea49c14ce84e6299f1401c7 --- .../2019-08-15-unordered-write.markdown | 56 +++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 docs/_posts/2019-08-15-unordered-write.markdown diff --git a/docs/_posts/2019-08-15-unordered-write.markdown b/docs/_posts/2019-08-15-unordered-write.markdown new file mode 100644 index 000000000..5f0eb2880 --- /dev/null +++ b/docs/_posts/2019-08-15-unordered-write.markdown @@ -0,0 +1,56 @@ +--- +title: Higher write throughput with `unordered_write` feature +layout: post +author: maysamyabandeh +category: blog +--- + +Since RocksDB 6.3, The `unordered_write=`true option together with WritePrepared transactions offers 34-42% higher write throughput compared to vanilla RocksDB. If the application can handle more relaxed ordering guarantees, the gain in throughput would increase to 63-131%. + +### Background + +Currently RocksDB API delivers the following powerful guarantees: +- Atomic reads: Either all of a write batch is visible to reads or none of it. +- Read-your-own writes: When a write thread returns to the user, a subsequent read by the same thread will be able to see its own writes. +- Immutable Snapshots: The reads visible to the snapshot are immutable in the sense that it will not be affected by any in-flight or future writes. + +### `unordered_write` + +The `unordered_write` feature, when turned on, relaxes the default guarantees of RocksDB. While it still gives read-your-own-write property, neither atomic reads nor the immutable snapshot properties are provided any longer. However, RocksDB users could still get read-your-own-write and immutable snapshots when using this feature in conjunction with TransactionDB configured with WritePrepared transactions and `two_write_queues`. You can read [here](https://github.com/facebook/rocksdb/wiki/unordered_write) to learn about the design of `unordered_write` and [here](https://github.com/facebook/rocksdb/wiki/WritePrepared-Transactions) to learn more about WritePrepared transactions. + +### How to use it? + +To get the same guarantees as vanilla RocksdB: + + DBOptions db_options; + db_options.unordered_write = true; + db_options.two_write_queues = true; + DB* db; + { + TransactionDBOptions txn_db_options; + txn_db_options.write_policy = TxnDBWritePolicy::WRITE_PREPARED; + txn_db_options.skip_concurrency_control = true; + TransactionDB* txn_db; + TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db); + db = txn_db; + } + db->Write(...); + +To get relaxed guarantees: + + DBOptions db_options; + db_options.unordered_write = true; + DB* db; + DB::Open(db_options, kDBPath, &db); + db->Write(...); + +# Benchmarks + + TEST_TMPDIR=/dev/shm/ ~/db_bench --benchmarks=fillrandom --threads=32 --num=10000000 -max_write_buffer_number=16 --max_background_jobs=64 --batch_size=8 --writes=3000000 -level0_file_num_compaction_trigger=99999 --level0_slowdown_writes_trigger=99999 --level0_stop_writes_trigger=99999 -enable_pipelined_write=false -disable_auto_compactions --transaction_db=true --unordered_write=1 --disable_wal=0 + +Throughput with `unordered_write`=true and using WritePrepared transaction: +- WAL: +42% +- No-WAL: +34% +Throughput with `unordered_write`=true +- WAL: +63% +- NoWAL: +131%