Options creation

Options object

class rocksdb.Options

Important

The default values mentioned here, describe the values of the C++ library only. This wrapper does not set any default value itself. So as soon as the rocksdb developers change a default value this document could be outdated. So if you really depend on a default value, double check it with the according version of the C++ library.

__init__(**kwargs)

All options mentioned below can also be passed as keyword-arguments in the constructor. For example:

import rocksdb

opts = rocksdb.Options(create_if_missing=True)
# is the same as
opts = rocksdb.Options()
opts.create_if_missing = True
create_if_missing

If True, the database will be created if it is missing.

Type: bool
Default: False
error_if_exists

If True, an error is raised if the database already exists.

Type: bool
Default: False
paranoid_checks

If True, the implementation will do aggressive checking of the data it is processing and will stop early if it detects any errors. This may have unforeseen ramifications: for example, a corruption of one DB entry may cause a large number of entries to become unreadable or for the entire DB to become unopenable. If any of the writes to the database fails (Put, Delete, Merge, Write), the database will switch to read-only mode and fail all other Write operations.

Type: bool
Default: False
write_buffer_size

Amount of data to build up in memory (backed by an unsorted log on disk) before converting to a sorted on-disk file.

Larger values increase performance, especially during bulk loads. Up to max_write_buffer_number write buffers may be held in memory at the same time, so you may wish to adjust this parameter to control memory usage. Also, a larger write buffer will result in a longer recovery time the next time the database is opened.

Type: int
Default: 4194304
max_write_buffer_number

The maximum number of write buffers that are built up in memory. The default is 2, so that when 1 write buffer is being flushed to storage, new writes can continue to the other write buffer.

Type: int
Default: 2
min_write_buffer_number_to_merge

The minimum number of write buffers that will be merged together before writing to storage. If set to 1, then all write buffers are fushed to L0 as individual files and this increases read amplification because a get request has to check in all of these files. Also, an in-memory merge may result in writing lesser data to storage if there are duplicate records in each of these individual write buffers.

Type: int
Default: 1
max_open_files

Number of open files that can be used by the DB. You may need to increase this if your database has a large working set (budget one open file per 2MB of working set).

Type: int
Default: 1000
block_cache

Control over blocks (user data is stored in a set of blocks, and a block is the unit of reading from disk).

If not None use the specified cache for blocks. If None, rocksdb will automatically create and use an 8MB internal cache.

Type: Instace of rocksdb.LRUCache
Default: None
block_cache_compressed

If not None use the specified cache for compressed blocks. If None, rocksdb will not use a compressed block cache.

Type: Instace of rocksdb.LRUCache
Default: None
block_size

Approximate size of user data packed per block. Note that the block size specified here corresponds to uncompressed data. The actual size of the unit read from disk may be smaller if compression is enabled. This parameter can be changed dynamically.

Type: int
Default: 4096
block_restart_interval

Number of keys between restart points for delta encoding of keys. This parameter can be changed dynamically. Most clients should leave this parameter alone.

Type: int
Default: 16
compression

Compress blocks using the specified compression algorithm. This parameter can be changed dynamically.

whole_key_filtering

If True, place whole keys in the filter (not just prefixes). This must generally be true for gets to be efficient.

Type: bool
Default: True
num_levels

Number of levels for this database

Type: int
Default: 7
level0_file_num_compaction_trigger

Number of files to trigger level-0 compaction. A value <0 means that level-0 compaction will not be triggered by number of files at all.

Type: int
Default: 4
level0_slowdown_writes_trigger

Soft limit on number of level-0 files. We start slowing down writes at this point. A value <0 means that no writing slow down will be triggered by number of files in level-0.

Type: int
Default: 8
level0_stop_writes_trigger

Maximum number of level-0 files. We stop writes at this point.

Type: int
Default: 12
max_mem_compaction_level

Maximum level to which a new compacted memtable is pushed if it does not create overlap. We try to push to level 2 to avoid the relatively expensive level 0=>1 compactions and to avoid some expensive manifest file operations. We do not push all the way to the largest level since that can generate a lot of wasted disk space if the same key space is being repeatedly overwritten.

Type: int
Default: 2
target_file_size_base
Target file size for compaction.
target_file_size_base is per-file size for level-1.
Target file size for level L can be calculated by
target_file_size_base * (target_file_size_multiplier ^ (L-1)).

For example, if target_file_size_base is 2MB and target_file_size_multiplier is 10, then each file on level-1 will be 2MB, and each file on level 2 will be 20MB, and each file on level-3 will be 200MB.

Type: int
Default: 2097152
target_file_size_multiplier
by default target_file_size_multiplier is 1, which means
by default files in different levels will have similar size.
Type: int
Default: 1
max_bytes_for_level_base

Control maximum total data size for a level. max_bytes_for_level_base is the max total for level-1. Maximum number of bytes for level L can be calculated as (max_bytes_for_level_base) * (max_bytes_for_level_multiplier ^ (L-1)) For example, if max_bytes_for_level_base is 20MB, and if max_bytes_for_level_multiplier is 10, total data size for level-1 will be 20MB, total file size for level-2 will be 200MB, and total file size for level-3 will be 2GB.

Type: int
Default: 10485760
max_bytes_for_level_multiplier

See max_bytes_for_level_base

Type: int
Default: 10
max_bytes_for_level_multiplier_additional

Different max-size multipliers for different levels. These are multiplied by max_bytes_for_level_multiplier to arrive at the max-size of each level.

Type: [int]
Default: [1, 1, 1, 1, 1, 1, 1]
expanded_compaction_factor

Maximum number of bytes in all compacted files. We avoid expanding the lower level file set of a compaction if it would make the total compaction cover more than (expanded_compaction_factor * targetFileSizeLevel()) many bytes.

Type: int
Default: 25
source_compaction_factor

Maximum number of bytes in all source files to be compacted in a single compaction run. We avoid picking too many files in the source level so that we do not exceed the total source bytes for compaction to exceed (source_compaction_factor * targetFileSizeLevel()) many bytes. If 1 pick maxfilesize amount of data as the source of a compaction.

Type: int
Default: 1
max_grandparent_overlap_factor

Control maximum bytes of overlaps in grandparent (i.e., level+2) before we stop building a single file in a level->level+1 compaction.

Type: int
Default: 10
disable_data_sync

If true, then the contents of data files are not synced to stable storage. Their contents remain in the OS buffers till the OS decides to flush them. This option is good for bulk-loading of data. Once the bulk-loading is complete, please issue a sync to the OS to flush all dirty buffesrs to stable storage.

Type: bool
Default: False
use_fsync

If true, then every store to stable storage will issue a fsync. If false, then every store to stable storage will issue a fdatasync. This parameter should be set to true while storing data to filesystem like ext3 that can lose files after a reboot.

Type: bool
Default: False
db_stats_log_interval

This number controls how often a new scribe log about db deploy stats is written out. -1 indicates no logging at all.

Type: int
Default: 1800
db_log_dir

This specifies the info LOG dir. If it is empty, the log files will be in the same dir as data. If it is non empty, the log files will be in the specified dir, and the db data dir’s absolute path will be used as the log file name’s prefix.

Type: unicode
Default: ""
wal_dir

This specifies the absolute dir path for write-ahead logs (WAL). If it is empty, the log files will be in the same dir as data, dbname is used as the data dir by default. If it is non empty, the log files will be in kept the specified dir. When destroying the db, all log files in wal_dir and the dir itself is deleted

Type: unicode
Default: ""
disable_seek_compaction

Disable compaction triggered by seek. With bloomfilter and fast storage, a miss on one level is very cheap if the file handle is cached in table cache (which is true if max_open_files is large).

Type: bool
Default: False
delete_obsolete_files_period_micros

The periodicity when obsolete files get deleted. The default value is 6 hours. The files that get out of scope by compaction process will still get automatically delete on every compaction, regardless of this setting

Type: int
Default: 21600000000
max_background_compactions

Maximum number of concurrent background jobs, submitted to the default LOW priority thread pool

Type: int
Default: 1
max_background_flushes

Maximum number of concurrent background memtable flush jobs, submitted to the HIGH priority thread pool. By default, all background jobs (major compaction and memtable flush) go to the LOW priority pool. If this option is set to a positive number, memtable flush jobs will be submitted to the HIGH priority pool. It is important when the same Env is shared by multiple db instances. Without a separate pool, long running major compaction jobs could potentially block memtable flush jobs of other db instances, leading to unnecessary Put stalls.

Type: int
Default: 0
max_log_file_size

Specify the maximal size of the info log file. If the log file is larger than max_log_file_size, a new info log file will be created. If max_log_file_size == 0, all logs will be written to one log file.

Type: int
Default: 0
log_file_time_to_roll

Time for the info log file to roll (in seconds). If specified with non-zero value, log file will be rolled if it has been active longer than log_file_time_to_roll. A value of 0 means disabled.

Type: int
Default: 0
keep_log_file_num

Maximal info log files to be kept.

Type: int
Default: 1000
soft_rate_limit

Puts are delayed 0-1 ms when any level has a compaction score that exceeds soft_rate_limit. This is ignored when == 0.0. CONSTRAINT: soft_rate_limit <= hard_rate_limit. If this constraint does not hold, RocksDB will set soft_rate_limit = hard_rate_limit. A value of 0 means disabled.

Type: float
Default: 0
hard_rate_limit

Puts are delayed 1ms at a time when any level has a compaction score that exceeds hard_rate_limit. This is ignored when <= 1.0. A value fo 0 means disabled.

Type: float
Default: 0
rate_limit_delay_max_milliseconds

Max time a put will be stalled when hard_rate_limit is enforced. If 0, then there is no limit.

Type: int
Default: 1000
max_manifest_file_size

manifest file is rolled over on reaching this limit. The older manifest file be deleted. The default value is MAX_INT so that roll-over does not take place.

Type: int
Default: (2**64) - 1
no_block_cache

Disable block cache. If this is set to true, then no block cache should be used, and the block_cache should point to None

Type: bool
Default: False
table_cache_numshardbits

Number of shards used for table cache.

Type: int
Default: 4
table_cache_remove_scan_count_limit

During data eviction of table’s LRU cache, it would be inefficient to strictly follow LRU because this piece of memory will not really be released unless its refcount falls to zero. Instead, make two passes: the first pass will release items with refcount = 1, and if not enough space releases after scanning the number of elements specified by this parameter, we will remove items in LRU order.

Type: int
Default: 16
arena_block_size

size of one block in arena memory allocation. If <= 0, a proper value is automatically calculated (usually 1/10 of writer_buffer_size).

Type: int
Default: 0
disable_auto_compactions

Disable automatic compactions. Manual compactions can still be issued on this database.

Type: bool
Default: False
wal_ttl_seconds, wal_size_limit_mb

The following two fields affect how archived logs will be deleted.

  1. If both set to 0, logs will be deleted asap and will not get into the archive.
  2. If wal_ttl_seconds is 0 and wal_size_limit_mb is not 0, WAL files will be checked every 10 min and if total size is greater then wal_size_limit_mb, they will be deleted starting with the earliest until size_limit is met. All empty files will be deleted.
  3. If wal_ttl_seconds is not 0 and wal_size_limit_mb is 0, then WAL files will be checked every wal_ttl_secondsi / 2 and those that are older than wal_ttl_seconds will be deleted.
  4. If both are not 0, WAL files will be checked every 10 min and both checks will be performed with ttl being first.
Type: int
Default: 0
manifest_preallocation_size

Number of bytes to preallocate (via fallocate) the manifest files. Default is 4mb, which is reasonable to reduce random IO as well as prevent overallocation for mounts that preallocate large amounts of data (such as xfs’s allocsize option).

Type: int
Default: 4194304
purge_redundant_kvs_while_flush

Purge duplicate/deleted keys when a memtable is flushed to storage.

Type: bool
Default: True
allow_os_buffer

Data being read from file storage may be buffered in the OS

Type: bool
Default: True
allow_mmap_reads

Allow the OS to mmap file for reading sst tables

Type: bool
Default: False
allow_mmap_writes

Allow the OS to mmap file for writing

Type: bool
Default: True
is_fd_close_on_exec

Disable child process inherit open files

Type: bool
Default: True
skip_log_error_on_recovery

Skip log corruption error on recovery (If client is ok with losing most recent changes)

Type: bool
Default: False
stats_dump_period_sec

If not zero, dump rocksdb.stats to LOG every stats_dump_period_sec

Type: int
Default: 3600
block_size_deviation

This is used to close a block before it reaches the configured ‘block_size’. If the percentage of free space in the current block is less than this specified number and adding a new record to the block will exceed the configured block size, then this block will be closed and the new record will be written to the next block.

Type: int
Default: 10
advise_random_on_open

If set true, will hint the underlying file system that the file access pattern is random, when a sst file is opened.

Type: bool
Default: True
use_adaptive_mutex

Use adaptive mutex, which spins in the user space before resorting to kernel. This could reduce context switch when the mutex is not heavily contended. However, if the mutex is hot, we could end up wasting spin time.

Type: bool
Default: False
bytes_per_sync

Allows OS to incrementally sync files to disk while they are being written, asynchronously, in the background. Issue one request for every bytes_per_sync written. 0 turns it off.

Type: int
Default: 0
filter_deletes

Use KeyMayExist API to filter deletes when this is true. If KeyMayExist returns false, i.e. the key definitely does not exist, then the delete is a noop. KeyMayExist only incurs in-memory look up. This optimization avoids writing the delete to storage when appropriate.

Type: bool
Default: False
max_sequential_skip_in_iterations

An iteration->Next() sequentially skips over keys with the same user-key unless this option is set. This number specifies the number of keys (with the same userkey) that will be sequentially skipped before a reseek is issued.

Type: int
Default: 8
inplace_update_support

Allows thread-safe inplace updates. Requires Updates if

  • key exists in current memtable
  • new sizeof(new_value) <= sizeof(old_value)
  • old_value for that key is a put i.e. kTypeValue
Type: bool
Default: False
inplace_update_num_locks
Number of locks used for inplace update.
Default: 10000, if inplace_update_support = true, else 0.
Type: int
Default: 10000
comparator

Comparator used to define the order of keys in the table. A python comparator must implement the rocksdb.interfaces.Comparator interface.

Requires: The client must ensure that the comparator supplied here has the same name and orders keys exactly the same as the comparator provided to previous open calls on the same DB.

Default: rocksdb.BytewiseComparator

merge_operator

The client must provide a merge operator if Merge operation needs to be accessed. Calling Merge on a DB without a merge operator would result in rocksdb.errors.NotSupported. The client must ensure that the merge operator supplied here has the same name and exactly the same semantics as the merge operator provided to previous open calls on the same DB. The only exception is reserved for upgrade, where a DB previously without a merge operator is introduced to Merge operation for the first time. It’s necessary to specify a merge operator when openning the DB in this case.

A python merge operator must implement the rocksdb.interfaces.MergeOperator or rocksdb.interfaces.AssociativeMergeOperator interface.

Default: None

filter_policy

If not None use the specified filter policy to reduce disk reads. A python filter policy must implement the rocksdb.interfaces.FilterPolicy interface. Recommendes is a instance of rocksdb.BloomFilterPolicy

Default: None

prefix_extractor

If not None, use the specified function to determine the prefixes for keys. These prefixes will be placed in the filter. Depending on the workload, this can reduce the number of read-IOP cost for scans when a prefix is passed to the calls generating an iterator (rocksdb.DB.iterkeys() ...).

A python prefix_extractor must implement the rocksdb.interfaces.SliceTransform interface

For prefix filtering to work properly, “prefix_extractor” and “comparator” must be such that the following properties hold:

  1. key.starts_with(prefix(key))
  2. compare(prefix(key), key) <= 0
  3. If compare(k1, k2) <= 0, then compare(prefix(k1), prefix(k2)) <= 0
  4. prefix(prefix(key)) == prefix(key)

Default: None

CompressionTypes

class rocksdb.CompressionType

Defines the support compression types

no_compression
snappy_compression
zlib_compression
bzip2_compression

BytewiseComparator

class rocksdb.BytewiseComparator

Wraps the rocksdb Bytewise Comparator, it uses lexicographic byte-wise ordering

BloomFilterPolicy

class rocksdb.BloomFilterPolicy

Wraps the rocksdb BloomFilter Policy

__init__(bits_per_key)
Parameters:bits_per_key (int) – Specifies the approximately number of bits per key. A good value for bits_per_key is 10, which yields a filter with ~ 1% false positive rate.

LRUCache

class rocksdb.LRUCache

Wraps the rocksdb LRUCache

__init__(capacity, shard_bits=None, rm_scan_count_limit=None)

Create a new cache with a fixed size capacity. The cache is sharded to 2^numShardBits shards, by hash of the key. The total capacity is divided and evenly assigned to each shard. Inside each shard, the eviction is done in two passes: first try to free spaces by evicting entries that are among the most least used removeScanCountLimit entries and do not have reference other than by the cache itself, in the least-used order. If not enough space is freed, further free the entries in least used order.