mini_lsm/mini-lsm/src/compact.rs

mod leveled;
mod simple_leveled;
mod tiered;

use std::sync::Arc;
use std::time::Duration;

use anyhow::Result;
pub use leveled::{LeveledCompactionController, LeveledCompactionOptions, LeveledCompactionTask};
use serde::{Deserialize, Serialize};
pub use simple_leveled::{
    SimpleLeveledCompactionController, SimpleLeveledCompactionOptions, SimpleLeveledCompactionTask,
};
pub use tiered::{TieredCompactionController, TieredCompactionOptions, TieredCompactionTask};

use crate::iterators::merge_iterator::MergeIterator;
use crate::iterators::StorageIterator;
use crate::lsm_storage::{LsmStorageInner, LsmStorageState};
use crate::manifest::ManifestRecord;
use crate::table::{SsTable, SsTableBuilder, SsTableIterator};

#[derive(Debug, Serialize, Deserialize)]
pub(crate) enum CompactionTask {
    Leveled(LeveledCompactionTask),
    Tiered(TieredCompactionTask),
    Simple(SimpleLeveledCompactionTask),
    ForceFullCompaction(Vec<usize>),
}

impl CompactionTask {
    fn compact_to_bottom_level(&self) -> bool {
        match self {
            CompactionTask::ForceFullCompaction(_) => true,
            CompactionTask::Leveled(task) => task.is_lower_level_bottom_level,
            CompactionTask::Simple(task) => task.is_lower_level_bottom_level,
            CompactionTask::Tiered(task) => task.bottom_tier_included,
        }
    }
}

pub(crate) enum CompactionController {
    Leveled(LeveledCompactionController),
    Tiered(TieredCompactionController),
    Simple(SimpleLeveledCompactionController),
    NoCompaction,
}

impl CompactionController {
    pub fn generate_compaction_task(&self, snapshot: &LsmStorageState) -> Option<CompactionTask> {
        match self {
            CompactionController::Leveled(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Leveled),
            CompactionController::Simple(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Simple),
            CompactionController::Tiered(ctrl) => ctrl
                .generate_compaction_task(&snapshot)
                .map(CompactionTask::Tiered),
            CompactionController::NoCompaction => unreachable!(),
        }
    }

    pub fn apply_compaction_result(
        &self,
        snapshot: &LsmStorageState,
        task: &CompactionTask,
        output: &[usize],
    ) -> (LsmStorageState, Vec<usize>) {
        match (self, task) {
            (CompactionController::Leveled(ctrl), CompactionTask::Leveled(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            (CompactionController::Simple(ctrl), CompactionTask::Simple(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            (CompactionController::Tiered(ctrl), CompactionTask::Tiered(task)) => {
                ctrl.apply_compaction_result(&snapshot, task, output)
            }
            _ => unreachable!(),
        }
    }
}

impl CompactionController {
    pub fn flush_to_l0(&self) -> bool {
        if let Self::Leveled(_) | Self::Simple(_) | Self::NoCompaction = self {
            true
        } else {
            false
        }
    }
}

pub enum CompactionOptions {
    /// Leveled compaction with partial compaction + dynamic level support (= RocksDB's Leveled
    /// Compaction)
    Leveled(LeveledCompactionOptions),
    /// Tiered compaction (= RocksDB's universal compaction)
    Tiered(TieredCompactionOptions),
    /// Simple leveled compaction
    Simple(SimpleLeveledCompactionOptions),
    /// In no compaction mode (week 1), always flush to L0
    NoCompaction,
}

impl LsmStorageInner {
    fn compact(&self, task: &CompactionTask) -> Result<Vec<Arc<SsTable>>> {
        let table_ids = match task {
            CompactionTask::Leveled(task) => task
                .lower_level_sst_ids
                .iter()
                .copied()
                .chain(task.upper_level_sst_ids.iter().copied())
                .collect::<Vec<_>>(),
            CompactionTask::Simple(task) => task
                .lower_level_sst_ids
                .iter()
                .copied()
                .chain(task.upper_level_sst_ids.iter().copied())
                .collect::<Vec<_>>(),
            CompactionTask::Tiered(task) => task
                .tiers
                .iter()
                .map(|(_, files)| files)
                .flatten()
                .copied()
                .collect::<Vec<_>>(),
            CompactionTask::ForceFullCompaction(l0_ssts) => l0_ssts.clone(),
        };
        let tables: Vec<Arc<SsTable>> = {
            let state = self.state.read();
            table_ids
                .iter()
                .map(|id| state.sstables.get(id).unwrap().clone())
                .collect::<Vec<_>>()
        };

        let mut iters = Vec::new();
        iters.reserve(tables.len());
        for table in tables.iter() {
            iters.push(Box::new(SsTableIterator::create_and_seek_to_first(
                table.clone(),
            )?));
        }
        let mut iter = MergeIterator::create(iters);

        let mut builder = None;
        let mut new_sst = vec![];

        let compact_to_bottom_level = task.compact_to_bottom_level();

        while iter.is_valid() {
            if builder.is_none() {
                builder = Some(SsTableBuilder::new(self.options.block_size));
            }
            let builder_inner = builder.as_mut().unwrap();
            if compact_to_bottom_level {
                if !iter.value().is_empty() {
                    builder_inner.add(iter.key(), iter.value());
                }
            } else {
                builder_inner.add(iter.key(), iter.value());
            }
            iter.next()?;

            if builder_inner.estimated_size() >= self.options.target_sst_size {
                let sst_id = self.next_sst_id(); // lock dropped here
                let builder = builder.take().unwrap();
                let sst = Arc::new(builder.build(
                    sst_id,
                    Some(self.block_cache.clone()),
                    self.path_of_sst(sst_id),
                )?);
                new_sst.push(sst);
            }
        }
        if let Some(builder) = builder {
            let sst_id = self.next_sst_id(); // lock dropped here
            let sst = Arc::new(builder.build(
                sst_id,
                Some(self.block_cache.clone()),
                self.path_of_sst(sst_id),
            )?);
            new_sst.push(sst);
        }
        Ok(new_sst)
    }

    pub fn force_full_compaction(&self) -> Result<()> {
        let CompactionOptions::NoCompaction = self.options.compaction_options else {
            panic!("full compaction can only be called with compaction is not enabled")
        };
        let snapshot = {
            let state = self.state.read();
            state.clone()
        };
        let mut original_sstables = snapshot.l0_sstables.clone();
        original_sstables.reverse();
        let sstables = self.compact(&CompactionTask::ForceFullCompaction(
            original_sstables.clone(),
        ))?;
        {
            let _state_lock = self.state_lock.lock();
            let mut state = self.state.read().as_ref().clone();
            for sst in original_sstables.iter() {
                let result = state.sstables.remove(sst);
                assert!(result.is_some());
            }
            let mut ids = Vec::with_capacity(sstables.len());
            for new_sst in sstables {
                ids.push(new_sst.sst_id());
                let result = state.sstables.insert(new_sst.sst_id(), new_sst);
                assert!(result.is_none());
            }
            state.l0_sstables = ids;
            *self.state.write() = Arc::new(state);
        }
        for sst in original_sstables {
            std::fs::remove_file(self.path_of_sst(sst))?;
        }
        Ok(())
    }

    fn trigger_compaction(&self) -> Result<()> {
        let snapshot = {
            let state = self.state.read();
            state.clone()
        };
        let task = self
            .compaction_controller
            .generate_compaction_task(&snapshot);
        let Some(task) = task else {
            return Ok(());
        };
        println!("running compaction task: {:?}", task);
        let sstables = self.compact(&task)?;
        let output = sstables.iter().map(|x| x.sst_id()).collect::<Vec<_>>();
        let ssts_to_remove = {
            let state_lock = self.state_lock.lock();
            let (mut snapshot, files_to_remove) = self
                .compaction_controller
                .apply_compaction_result(&self.state.read(), &task, &output);
            let mut ssts_to_remove = Vec::with_capacity(files_to_remove.len());
            for file_to_remove in &files_to_remove {
                let result = snapshot.sstables.remove(file_to_remove);
                assert!(result.is_some());
                ssts_to_remove.push(result.unwrap());
            }
            let mut new_sst_ids = Vec::new();
            for file_to_add in sstables {
                new_sst_ids.push(file_to_add.sst_id());
                let result = snapshot.sstables.insert(file_to_add.sst_id(), file_to_add);
                assert!(result.is_none());
            }
            let mut state = self.state.write();
            *state = Arc::new(snapshot);
            self.manifest
                .add_record(&state_lock, ManifestRecord::Compaction(task, new_sst_ids))?;
            ssts_to_remove
        };
        for sst in ssts_to_remove {
            std::fs::remove_file(self.path_of_sst(sst.sst_id()))?;
        }
        Ok(())
    }

    pub(crate) fn spawn_compaction_thread(
        self: &Arc<Self>,
        rx: crossbeam_channel::Receiver<()>,
    ) -> Result<Option<std::thread::JoinHandle<()>>> {
        if let CompactionOptions::Leveled(_)
        | CompactionOptions::Simple(_)
        | CompactionOptions::Tiered(_) = self.options.compaction_options
        {
            let this = self.clone();
            let handle = std::thread::spawn(move || {
                let ticker = crossbeam_channel::tick(Duration::from_millis(50));
                loop {
                    crossbeam_channel::select! {
                        recv(ticker) -> _ => if let Err(e) = this.trigger_compaction() {
                            eprintln!("compaction failed: {}", e);
                        },
                        recv(rx) -> _ => return
                    }
                }
            });
            return Ok(Some(handle));
        }
        Ok(None)
    }
}