Options reference

Every database-wide and per-keyspace option with its default, and the presets for point lookups, write-heavy keyspaces and bulk loads.

Options are validated when built. A value out of range is refused with Error::InvalidOptions, naming the option. The full list, with every bound, is in the API reference.

Database options

Set through DbOptions::builder().

Option	Default	What it sets
`create_if_missing`	`true`	create the database when the path holds none
`error_if_exists`	`false`	refuse to open a database that already exists
`storage`	`StorageMode::Os`	files on disk, or `Memory` (`DbOptions::in_memory()`)
`wal_segment_bytes`	64 MiB	size at which a log segment is closed and the next started
`wal_recovery`	`PointInTime`	what opening does with a damaged log end
`block_cache_bytes`	512 MiB	block cache shared by every keyspace; zero disables it
`background_threads`	4	threads running flushes and compactions
`compaction_bytes_per_second`	0 (unpaced)	pace of compaction output
`delayed_write_bytes_per_second`	16 MiB/s	pace of writes while slowed down
`serializable_transactions`	`false`	allow `Isolation::Serializable`
`total_memtable_bytes`	0 (no ceiling)	cap on the newest in-memory tables of every keyspace together
`max_open_files`	0 (no bound)	table files kept open at once
`max_manifest_bytes`	64 MiB	size past which the manifest is rewritten; bounds open time
`statistics`	`false`	count tickers and histograms
`encryption(provider, key_id)`	off	encryption at rest
`encryption_cipher`	by processor	pin AES-256-GCM or ChaCha20-Poly1305
`default_keyspace`	defaults	options of the default keyspace
`keyspace(name, options)`	—	name a keyspace to open
`create_missing_keyspaces`	`false`	add named keyspaces the database does not hold

Keyspace options

Set through KeyspaceOptions::builder().

Option	Default	What it sets
`memtable_bytes`	64 MiB	in-memory table size before it is frozen
`max_immutable_memtables`	2	frozen tables that may wait for a flush
`block_bytes`	4 KiB	data block size before compression
`block_restart_interval`	16	keys between two whole keys in a block
`bloom_bits_per_key`	10	bloom filter size; zero writes no filter
`compression`	`Lz4`	`None`, `Lz4`, `Snappy`, `Zstd` or `Deflate { level }`
`bottommost_compression`	`None` (same as above)	a separate codec for the bottom level
`compaction`	`Leveled`	`Leveled`, `universal()` or `fifo()`
`level0_compaction_trigger`	4	level-0 tables that start a compaction
`level0_slowdown_trigger`	20	level-0 tables at which writes slow down
`level0_stop_trigger`	36	level-0 tables at which writes stop
`soft_pending_compaction_bytes`	64 GiB	compaction debt at which writes slow down
`hard_pending_compaction_bytes`	256 GiB	compaction debt at which writes stop
`level_base_bytes`	256 MiB	target size of the first level below level 0
`level_size_multiplier`	10	growth from one level to the next
`target_file_bytes`	64 MiB	size at which compaction closes an output table
`max_compactions`	4	compactions of the keyspace at once
`max_subcompactions`	4	parallel parts of one compaction
`disable_auto_compactions`	`false`	no compaction unless asked for, for bulk loads

Presets

Preset	For	Sets
`KeyspaceOptions::point_lookup()`	mostly point reads	16 bloom bits per key, about 0.1 % false positives
`KeyspaceOptions::write_heavy()`	mostly writes	256 MiB in-memory tables, up to four waiting for a flush
`KeyspaceOptions::bulk_load()`	one large load	512 MiB in-memory tables, up to six waiting, 64 KiB blocks

Start from a preset and adjust it with to_builder().

Per-write, per-read, per-transaction

WriteOptions — durability, no_slowdown. See Writes and durability.
ReadOptions — verify_checksums, fill_cache, lower_bound, upper_bound. See Reads and snapshots.
TransactionOptions — isolation. See Transactions.