Struct lsm_tree::compaction::Levelled

pub struct Levelled {
    pub l0_threshold: u8,
    pub target_size: u32,
}

Levelled compaction strategy (LCS)

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

Each level Ln for n >= 1 can have up to ratio^n segments.

LCS suffers from high write amplification, but decent read & space amplification.

More info here: https://opensource.docs.scylladb.com/stable/cql/compaction.html#leveled-compaction-strategy-lcs

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

Target segment size (compressed)

Default = 64 MiB

Same as target_file_size_base in RocksDB

Trait Implementations

impl CompactionStrategy for Strategy

fn choose(&self, levels: &Levels, config: &PersistedConfig) -> 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.