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56 lines
2.7 KiB
56 lines
2.7 KiB
---
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title: Higher write throughput with `unordered_write` feature
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layout: post
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author: maysamyabandeh
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category: blog
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---
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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%.
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### Background
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Currently RocksDB API delivers the following powerful guarantees:
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- Atomic reads: Either all of a write batch is visible to reads or none of it.
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- 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.
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- 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.
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### `unordered_write`
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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.
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### How to use it?
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To get the same guarantees as vanilla RocksdB:
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DBOptions db_options;
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db_options.unordered_write = true;
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db_options.two_write_queues = true;
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DB* db;
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{
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TransactionDBOptions txn_db_options;
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txn_db_options.write_policy = TxnDBWritePolicy::WRITE_PREPARED;
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txn_db_options.skip_concurrency_control = true;
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TransactionDB* txn_db;
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TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db);
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db = txn_db;
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}
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db->Write(...);
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To get relaxed guarantees:
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DBOptions db_options;
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db_options.unordered_write = true;
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DB* db;
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DB::Open(db_options, kDBPath, &db);
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db->Write(...);
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# Benchmarks
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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
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Throughput with `unordered_write`=true and using WritePrepared transaction:
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- WAL: +42%
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- No-WAL: +34%
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Throughput with `unordered_write`=true
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- WAL: +63%
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- NoWAL: +131%
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