coordinode-lsm-tree 4.3.1

// Copyright (c) 2024-present, fjall-rs
// This source code is licensed under both the Apache 2.0 and MIT License
// (found in the LICENSE-* files in the repository)

//! Contains compaction strategies

pub(crate) mod fifo;
pub(crate) mod leveled;
// pub(crate) mod maintenance;
pub(crate) mod drop_range;
pub mod filter;
mod flavour;
pub(crate) mod major;
pub(crate) mod movedown;
pub(crate) mod pulldown;
pub(crate) mod state;
pub(crate) mod stream;
pub(crate) mod tiered;
pub(crate) mod worker;

pub use fifo::Strategy as Fifo;
pub use filter::{CompactionFilter, Factory, ItemAccessor, Verdict};
pub use leveled::Strategy as Leveled;
pub use tiered::Strategy as SizeTiered;

pub use {
    fifo::NAME as FIFO_COMPACTION_NAME, leveled::NAME as LEVELED_COMPACTION_NAME,
    tiered::NAME as TIERED_COMPACTION_NAME,
};

/// Alias for `Leveled`
pub type Levelled = Leveled;

#[doc(hidden)]
pub use movedown::Strategy as MoveDown;

#[doc(hidden)]
pub use pulldown::Strategy as PullDown;

use crate::{
    HashSet, KvPair, TableId, compaction::state::CompactionState, config::Config, version::Version,
};

/// The action taken during a compaction run.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CompactionAction {
    /// Strategy chose to do nothing.
    Nothing,

    /// Tables were merged (rewritten) into a destination level.
    Merged,

    /// Tables were moved to a deeper level without rewriting.
    Moved,

    /// Tables were dropped without compaction.
    Dropped,
}

/// Result of a compaction operation, describing what happened.
///
/// Returned by [`crate::AbstractTree::compact`] to give callers
/// observability into which compaction path was taken.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct CompactionResult {
    /// The action that was taken.
    pub action: CompactionAction,

    /// The destination level, if applicable.
    pub dest_level: Option<u8>,

    /// Number of input tables consumed.
    pub tables_in: usize,

    /// Number of output tables produced.
    pub tables_out: usize,
}

impl CompactionResult {
    /// Creates a result for the "do nothing" case.
    #[must_use]
    pub fn nothing() -> Self {
        Self {
            action: CompactionAction::Nothing,
            dest_level: None,
            tables_in: 0,
            tables_out: 0,
        }
    }
}

/// Input for compactor
///
/// The compaction strategy chooses which tables to compact and how.
/// That information is given to the compactor.
#[derive(Debug, Eq, PartialEq)]
pub struct Input {
    /// Tables to compact
    pub table_ids: HashSet<TableId>,

    /// Level to put the created tables into
    pub dest_level: u8,

    /// The logical level the tables are part of
    pub canonical_level: u8,

    /// Table target size
    ///
    /// If a table merge reaches the size threshold, a new table is started.
    /// This results in a sorted "run" of tables.
    pub target_size: u64,
}

/// Describes what to do (compact or not)
#[derive(Debug, Eq, PartialEq)]
pub enum Choice {
    /// Just do nothing.
    DoNothing,

    /// Moves tables into another level without rewriting.
    Move(Input),

    /// Compacts some tables into a new level.
    Merge(Input),

    /// Delete tables without doing compaction.
    ///
    /// This may be used by a compaction strategy that wants to delete old data
    /// without having to compact it away, like [`fifo::Strategy`].
    Drop(HashSet<TableId>),
}

/// Trait for a compaction strategy
///
/// The strategy receives the levels of the LSM-tree as argument
/// and emits a choice on what to do.
#[expect(clippy::module_name_repetitions)]
pub trait CompactionStrategy {
    /// Gets the compaction strategy name.
    fn get_name(&self) -> &'static str;

    #[doc(hidden)]
    fn get_config(&self) -> Vec<KvPair> {
        vec![]
    }

    /// Decides on what to do based on the current state of the LSM-tree's levels
    fn choose(&self, version: &Version, config: &Config, state: &CompactionState) -> Choice;
}