Struct Leveled 

pub struct Leveled { /* private fields */ }

Leveled compaction strategy (LCS)

When a level reaches some threshold size, parts of it are merged into overlapping tables in the next level.

Each level Ln for n >= 2 can have up to level_base_size * ratio^(n - 1) tables.

LCS suffers from comparatively high write amplification, but has decent read amplification and great space amplification (~1.1x).

LCS is the recommended compaction strategy to use.

More info here: https://fjall-rs.github.io/post/lsm-leveling/

Implementations

impl Strategy

pub fn with_level_ratio_policy(self, policy: Vec<f32>) -> Self

Sets the growth ratio between levels.

Same as set_max_bytes_for_level_multiplier in RocksDB.

Default = [10.0]

pub fn with_l0_threshold(self, threshold: u8) -> Self

Sets the L0 threshold.

When the number of tables in L0 reaches this threshold, they are merged into L1.

Same as level0_file_num_compaction_trigger in RocksDB.

Default = 4

pub fn with_table_target_size(self, bytes: u64) -> Self

Sets the table target size on disk (possibly compressed).

Same as target_file_size_base in RocksDB.

Default = 64 MiB

pub fn with_dynamic_level_bytes(self, enabled: bool) -> Self

Enables dynamic level sizing based on actual data in the last level.

When enabled, level target sizes are computed top-down from the actual size of the last non-empty level, divided by the ratio at each step. This reduces space amplification to ~1.1x while keeping write amplification comparable to static leveling.

Same as level_compaction_dynamic_level_bytes in RocksDB.

Default = false

pub fn with_multi_level(self, enabled: bool) -> Self

Enables multi-level compaction optimization.

When L0→L1 compaction is selected but L1 already exceeds its target size, this option allows compacting L0+L1 directly into L2 in one pass, avoiding the write-then-rewrite cycle that would otherwise occur.

Default = false

Trait Implementations

impl Clone for Strategy

fn clone(&self) -> Strategy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl CompactionStrategy for Strategy

fn get_name(&self) -> &'static str

Gets the compaction strategy name.

fn pending_compaction_bytes(&self, version: &Version) -> u64

Estimated bytes pending compaction: on-disk data currently sitting above its level’s target size that must eventually be rewritten downward (a RocksDB estimate-pending-compaction-bytes analog). A scheduler / tiering consumer reads it as a compaction-debt signal; 0 means the tree is at or below its target shape.

fn choose( &self, version: &Version, config: &Config, state: &CompactionState, ) -> Choice

Decides on what to do based on the current state of the LSM-tree’s levels

impl Default for Strategy

fn default() -> Self

Returns the “default value” for a type.