Struct Leveled

pub struct Leveled {
    pub l0_threshold: u8,
    pub target_size: u32,
    pub level_ratio: u8,
}

Levelled compaction strategy (LCS)

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

Each level Ln for n >= 2 can have up to level_base_size * ratio^n segments.

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/

Fields

l0_threshold: u8

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

Default = 4

Same as level0_file_num_compaction_trigger in RocksDB.

target_size: u32

The target segment size as disk (possibly compressed).

Default = 64 MiB

Same as target_file_size_base in RocksDB.

level_ratio: u8

Size ratio between levels of the LSM tree (a.k.a fanout, growth rate)

This is the exponential growth of the from one. level to the next

A level target size is: max_memtable_size * level_ratio.pow(#level + 1).

Trait Implementations

impl Clone for Strategy

fn clone(&self) -> Strategy

Returns a copy 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 choose(&self, levels: &LevelManifest, _: &Config) -> 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.