5.3 KiB
RocksDB engine options
RocksDB is a highly configurable key-value store used to power our RocksDB storage engine. Most of the options on this page are pass-through options to the underlying RocksDB instance, and we change very few of their default settings.
Pass-through options
Write buffers
--rocksdb.write-buffer-size
The amount of data to build up in each in-memory buffer (backed by a log file) before closing the buffer and queueing it to be flushed into standard storage. Default: 64MiB. Larger values may improve performance, especially for bulk loads.
--rocksdb.max-write-buffer-number
The maximum number of write buffers that built up in memory. If this number is reached before the buffers can be flushed, writes will be slowed or stalled. Default: 2.
--rocksdb.min-write-buffer-number-to-merge
Minimum number of write buffers that will be merged together when flushing to normal storage. Default: 1.
--rocksdb.delayed-write-rate (Hidden)
Limited write rate to DB (in bytes per second) if we are writing to the last in-memory buffer allowed and we allow more than 3 buffers. Default: 16MiB/s.
LSM tree structure
--rocksdb.num-levels
The number of levels for the database in the LSM tree. Default: 7.
--rocksdb.max-bytes-for-level-base (Hidden)
The maximum total data size in bytes in level-1 of the LSM tree. Default: 256MiB.
--rocksdb.max-bytes-for-level-multiplier
The maximum total data size in bytes for level L of the LSM tree can be
calculated as max-bytes-for-level-base * (max-bytes-for-level-multiplier ^ (L-1)). Default: 10.
File I/O
--rocksdb.compaction-read-ahead-size (Hidden)
If non-zero, we perform bigger reads when doing compaction. If you're running RocksDB on spinning disks, you should set this to at least 2MiB. That way RocksDB's compaction is doing sequential instead of random reads. Default: 0.
--rocksdb.use-direct-reads (Hidden)
Only meaningful on Linux. If set, use O_DIRECT for reading files. Default:
false.
--rocksdb.use-direct-writes (Hidden)
Only meaningful on Linux. If set,use O_DIRECT for writing files. Default:
true.
--rocksdb.use-fsync (Hidden)
If set, issue an fsync call when writing to disk (set to false to issue
fdatasync only. Default: false.
Background tasks
--rocksdb.base-background-compactions (Hidden)
Suggested number of concurrent background compaction jobs, submitted to the low priority thread pool. Default: 1.
--rocksdb.max-background-compactions
Maximum number of concurrent background compaction jobs, submitted to the low priority thread pool. Default: 1.
--rocksdb.max-background-flushes
Maximum number of concurrent flush operations, submitted to the high priority thread pool. Default: 1.
--rocksdb.num-threads-priority-high
Number of threads for high priority operations (e.g. flush). We recommend
setting this equal to max-background-flushes. Default: 1.
--rocksdb.num-threads-priority-low
Number of threads for low priority operations (e.g. compaction). We recommend
setting this equal to max-background-compactions. Default: 1.
Caching
--rocksdb.block-cache-size
This is the size of the block cache in bytes. Increasing this may improve
performance. If there is less than 4GiB of RAM on the system, the default value
is 256MiB. If there is more, the default is (system RAM size - 2GiB) * 0.3.
--rocksdb.block-cache-shard-bits
The number of bits used to shard the block cache to allow concurrent operations.
To keep individual shards at a reasonable size (i.e. at least 512KB), keep this
value to at most block-cache-shard-bits / 512KB. Default: block-cache-size / 2^19.
--rocksdb.table-block-size
Approximate size of user data (in bytes) packed per block for uncompressed data.
--rocksdb.recycle-log-file-num (Hidden)
Number of log files to keep around for recycling. Default: 0.
Miscellaneous
--rocksdb.verify-checksums-in-compaction (Hidden)
If true, compaction will verify the data checksum on every read that happens as part of compaction. Default: true;
--rocksdb.optimize-filters-for-hits (Hidden)
This flag specifies that the implementation should optimize the filters mainly for cases where keys are found rather than also optimize for the case where keys are not. This would be used in cases where the application knows that there are very few misses or the performance in the case of misses is not as important. Default: false.
--rocksdb.wal-recovery-skip-corrupted (Hidden)
If true, skip corrupted records in WAL recovery. Default: false.
Non-Pass-Through Options
--rocksdb.max-transaction-size
Transaction size limit (in bytes). Transactions store all keys and values in
RAM, so large transactions run the risk of causing out-of-memory sitations.
This setting allows you to ensure that does not happen by limiting the size of
any individual transaction. Default: UINT64_MAX (2^64 - 1).
--rocksdb.intermediate-transaction (Hidden)
Enable intermediate commits. Default: false.
--rocksdb.intermediate-transaction-count (Hidden)
If intermediate commits are enabled, one will be tried when a transaction has accumulated operations totalling this size (in bytes). Default: 32MiB.
--rocksdb.wal-file-timeout (Hidden)
Timeout after which unused WAL files are deleted (in seconds). Default: 10.0s.