mini_lsm/mini-lsm/src/lsm_storage.rs

use std::collections::{BTreeSet, HashMap, HashSet};
use std::fs::File;
use std::ops::Bound;
use std::path::{Path, PathBuf};
use std::sync::atomic::AtomicUsize;
use std::sync::Arc;

use anyhow::{Context, Result};
use bytes::Bytes;
use parking_lot::{Mutex, RwLock};

use crate::block::Block;
use crate::compact::{
    CompactionController, CompactionOptions, LeveledCompactionController, LeveledCompactionOptions,
    SimpleLeveledCompactionController, SimpleLeveledCompactionOptions, TieredCompactionController,
};
use crate::iterators::merge_iterator::MergeIterator;
use crate::iterators::two_merge_iterator::TwoMergeIterator;
use crate::iterators::StorageIterator;
use crate::lsm_iterator::{FusedIterator, LsmIterator};
use crate::manifest::{Manifest, ManifestRecord};
use crate::mem_table::{map_bound, MemTable};
use crate::table::{self, FileObject, SsTable, SsTableBuilder, SsTableIterator};

pub type BlockCache = moka::sync::Cache<(usize, usize), Arc<Block>>;

#[derive(Clone)]
pub struct LsmStorageState {
    /// The current memtable.
    pub memtable: Arc<MemTable>,
    /// Immutable memtables, from earliest to latest.
    pub imm_memtables: Vec<Arc<MemTable>>,
    /// L0 SSTs, from earliest to latest.
    pub l0_sstables: Vec<usize>,
    /// SsTables sorted by key range; L1 - L_max for leveled compaction, or tiers for tiered
    /// compaction.
    pub levels: Vec<(usize, Vec<usize>)>,
    /// SST objects.
    pub sstables: HashMap<usize, Arc<SsTable>>,
}

impl LsmStorageState {
    fn create(options: &LsmStorageOptions) -> Self {
        let levels = match &options.compaction_options {
            CompactionOptions::Leveled(LeveledCompactionOptions { max_levels, .. })
            | CompactionOptions::Simple(SimpleLeveledCompactionOptions { max_levels, .. }) => (1
                ..=*max_levels)
                .map(|level| (level, Vec::new()))
                .collect::<Vec<_>>(),
            CompactionOptions::Tiered(_) | CompactionOptions::NoCompaction => Vec::new(),
        };
        Self {
            memtable: Arc::new(MemTable::create(0)),
            imm_memtables: Vec::new(),
            l0_sstables: Vec::new(),
            levels,
            sstables: Default::default(),
        }
    }
}

pub struct LsmStorageOptions {
    pub block_size: usize,
    pub target_sst_size: usize,
    pub compaction_options: CompactionOptions,
    pub enable_wal: bool,
}

impl LsmStorageOptions {
    pub fn default_for_week1_test() -> Self {
        Self {
            block_size: 4096,
            target_sst_size: 2 << 20,
            compaction_options: CompactionOptions::NoCompaction,
            enable_wal: false,
        }
    }
}

/// The storage interface of the LSM tree.
pub(crate) struct LsmStorageInner {
    pub(crate) state: Arc<RwLock<Arc<LsmStorageState>>>,
    pub(crate) state_lock: Mutex<()>,
    path: PathBuf,
    pub(crate) block_cache: Arc<BlockCache>,
    next_sst_id: AtomicUsize,
    pub(crate) options: Arc<LsmStorageOptions>,
    pub(crate) compaction_controller: CompactionController,
    pub(crate) manifest: Manifest,
}

pub struct MiniLsm {
    pub(crate) inner: Arc<LsmStorageInner>,
    compaction_notifier: crossbeam_channel::Sender<()>,
    compaction_thread: Mutex<Option<std::thread::JoinHandle<()>>>,
}

impl Drop for MiniLsm {
    fn drop(&mut self) {
        self.compaction_notifier.send(()).ok();
    }
}

impl MiniLsm {
    pub fn close(&self) -> Result<()> {
        self.inner.sync_dir()?;
        self.compaction_notifier.send(()).ok();
        let mut compaction_thread = self.compaction_thread.lock();
        if let Some(compaction_thread) = compaction_thread.take() {
            compaction_thread
                .join()
                .map_err(|e| anyhow::anyhow!("{:?}", e))?;
        }
        Ok(())
    }

    pub fn open(path: impl AsRef<Path>, options: LsmStorageOptions) -> Result<Arc<Self>> {
        let inner = Arc::new(LsmStorageInner::open(path, options)?);
        let (tx, rx) = crossbeam_channel::unbounded();
        let compaction_thread = inner.spawn_compaction_thread(rx)?;
        Ok(Arc::new(Self {
            inner,
            compaction_notifier: tx,
            compaction_thread: Mutex::new(compaction_thread),
        }))
    }

    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
        self.inner.get(key)
    }

    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
        self.inner.put(key, value)
    }

    pub fn delete(&self, key: &[u8]) -> Result<()> {
        self.inner.delete(key)
    }

    pub fn scan(
        &self,
        lower: Bound<&[u8]>,
        upper: Bound<&[u8]>,
    ) -> Result<FusedIterator<LsmIterator>> {
        self.inner.scan(lower, upper)
    }

    pub fn force_flush(&self) -> Result<()> {
        self.inner.force_freeze_memtable()?;
        self.inner.force_flush_next_imm_memtable()
    }
}

impl LsmStorageInner {
    pub(crate) fn next_sst_id(&self) -> usize {
        self.next_sst_id
            .fetch_add(1, std::sync::atomic::Ordering::SeqCst)
    }

    pub(crate) fn open(path: impl AsRef<Path>, options: LsmStorageOptions) -> Result<Self> {
        let mut state = LsmStorageState::create(&options);
        let path = path.as_ref();
        let mut next_sst_id = 1;
        let block_cache = Arc::new(BlockCache::new(1 << 20)); // 4GB block cache,
        let manifest;

        let compaction_controller = match &options.compaction_options {
            CompactionOptions::Leveled(options) => {
                CompactionController::Leveled(LeveledCompactionController::new(options.clone()))
            }
            CompactionOptions::Tiered(options) => {
                CompactionController::Tiered(TieredCompactionController::new(options.clone()))
            }
            CompactionOptions::Simple(options) => CompactionController::Simple(
                SimpleLeveledCompactionController::new(options.clone()),
            ),
            CompactionOptions::NoCompaction => CompactionController::NoCompaction,
        };

        if !path.exists() {
            std::fs::create_dir_all(path).context("failed to create DB dir")?;
            if options.enable_wal {
                state.memtable = Arc::new(MemTable::create_with_wal(
                    state.memtable.id(),
                    Self::path_of_wal_static(path, state.memtable.id()),
                )?);
            }
            manifest =
                Manifest::create(path.join("MANIFEST")).context("failed to create manifest")?;
            manifest.add_record_when_init(ManifestRecord::NewMemtable(state.memtable.id()))?;
        } else {
            let (m, records) = Manifest::recover(path.join("MANIFEST"))?;
            let mut memtables = BTreeSet::new();
            for record in records {
                match record {
                    ManifestRecord::Flush(sst_id) => {
                        let res = memtables.remove(&sst_id);
                        assert!(res, "memtable not exist?");
                        state.l0_sstables.insert(0, sst_id);
                    }
                    ManifestRecord::NewMemtable(x) => {
                        next_sst_id = x + 1;
                        memtables.insert(x);
                    }
                    ManifestRecord::Compaction(task, output) => {
                        let (new_state, _) =
                            compaction_controller.apply_compaction_result(&state, &task, &output);
                        // TODO: apply remove again
                        state = new_state;
                    }
                }
            }
            // recover SSTs
            for table_id in state
                .l0_sstables
                .iter()
                .chain(state.levels.iter().map(|(_, files)| files).flatten())
            {
                let table_id = *table_id;
                let sst = SsTable::open(
                    table_id,
                    Some(block_cache.clone()),
                    FileObject::open(&Self::path_of_sst_static(path, table_id))
                        .context("failed to open SST")?,
                )?;
                state.sstables.insert(table_id, Arc::new(sst));
            }
            // recover memtables
            if options.enable_wal {
                for id in memtables.iter() {
                    let memtable =
                        MemTable::recover_from_wal(*id, Self::path_of_wal_static(path, *id))?;
                    state.imm_memtables.insert(0, Arc::new(memtable));
                    next_sst_id = *id + 1;
                }
                state.memtable = Arc::new(MemTable::create_with_wal(
                    next_sst_id,
                    Self::path_of_wal_static(path, next_sst_id),
                )?);
            } else {
                state.memtable = Arc::new(MemTable::create(next_sst_id));
            }
            m.add_record_when_init(ManifestRecord::NewMemtable(state.memtable.id()))?;
            next_sst_id += 1;
            manifest = m;
        };

        let storage = Self {
            state: Arc::new(RwLock::new(Arc::new(state))),
            state_lock: Mutex::new(()),
            path: path.to_path_buf(),
            block_cache,
            next_sst_id: AtomicUsize::new(next_sst_id),
            compaction_controller,
            manifest,
            options: options.into(),
        };
        storage.sync_dir()?;

        Ok(storage)
    }

    /// Get a key from the storage. In day 7, this can be further optimized by using a bloom filter.
    pub fn get(&self, key: &[u8]) -> Result<Option<Bytes>> {
        let snapshot = {
            let guard = self.state.read();
            Arc::clone(&guard)
        }; // drop global lock here

        // Search on the current memtable.
        if let Some(value) = snapshot.memtable.get(key) {
            if value.is_empty() {
                // found tomestone, return key not exists
                return Ok(None);
            }
            return Ok(Some(value));
        }

        // Search on immutable memtables.
        for memtable in snapshot.imm_memtables.iter() {
            if let Some(value) = memtable.get(key) {
                if value.is_empty() {
                    // found tomestone, return key not exists
                    return Ok(None);
                }
                return Ok(Some(value));
            }
        }
        let mut iters = Vec::with_capacity(snapshot.l0_sstables.len());
        for table in snapshot
            .l0_sstables
            .iter()
            .chain(snapshot.levels.iter().map(|(_, files)| files).flatten())
        {
            iters.push(Box::new(SsTableIterator::create_and_seek_to_key(
                snapshot.sstables[table].clone(),
                key,
            )?));
        }
        let iter = MergeIterator::create(iters);
        if iter.is_valid() && iter.key() == key {
            return Ok(Some(Bytes::copy_from_slice(iter.value())));
        }
        Ok(None)
    }

    /// Put a key-value pair into the storage by writing into the current memtable.
    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
        assert!(!value.is_empty(), "value cannot be empty");
        assert!(!key.is_empty(), "key cannot be empty");

        let guard = self.state.read();
        guard.memtable.put(key, value)?;

        Ok(())
    }

    /// Remove a key from the storage by writing an empty value.
    pub fn delete(&self, key: &[u8]) -> Result<()> {
        assert!(!key.is_empty(), "key cannot be empty");

        let guard = self.state.read();
        guard.memtable.put(key, b"")?;

        Ok(())
    }

    pub(crate) fn path_of_sst_static(path: impl AsRef<Path>, id: usize) -> PathBuf {
        path.as_ref().join(format!("{:05}.sst", id))
    }

    pub(crate) fn path_of_sst(&self, id: usize) -> PathBuf {
        Self::path_of_sst_static(&self.path, id)
    }

    pub(crate) fn path_of_wal_static(path: impl AsRef<Path>, id: usize) -> PathBuf {
        path.as_ref().join(format!("{:05}.wal", id))
    }

    pub(crate) fn path_of_wal(&self, id: usize) -> PathBuf {
        Self::path_of_wal_static(&self.path, id)
    }

    fn sync_dir(&self) -> Result<()> {
        File::open(&self.path)?.sync_all()?;
        Ok(())
    }

    /// Force freeze the current memetable to an immutable memtable
    pub fn force_freeze_memtable(&self) -> Result<()> {
        let state_lock = self.state_lock.lock();

        let memtable_id = self.next_sst_id();
        let memtable = Arc::new(if self.options.enable_wal {
            let mt = MemTable::create_with_wal(memtable_id, self.path_of_wal(memtable_id))?;
            self.sync_dir()?;
            mt
        } else {
            MemTable::create(memtable_id)
        });

        let old_memtable;
        {
            let mut guard = self.state.write();
            // Swap the current memtable with a new one.
            let mut snapshot = guard.as_ref().clone();
            old_memtable = std::mem::replace(&mut snapshot.memtable, memtable);
            // Add the memtable to the immutable memtables.
            snapshot.imm_memtables.insert(0, old_memtable.clone());
            // Update the snapshot.
            *guard = Arc::new(snapshot);
        }
        old_memtable.sync_wal()?;

        self.manifest
            .add_record(&state_lock, ManifestRecord::NewMemtable(memtable_id))?;

        Ok(())
    }

    /// Force flush the earliest-created immutable memtable to disk
    pub fn force_flush_next_imm_memtable(&self) -> Result<()> {
        let state_lock = self.state_lock.lock();

        let flush_memtable;

        {
            let guard = self.state.read();
            flush_memtable = guard
                .imm_memtables
                .last()
                .expect("no imm memtables!")
                .clone();
        }

        let mut builder = SsTableBuilder::new(self.options.block_size);
        flush_memtable.flush(&mut builder)?;
        let sst_id = flush_memtable.id();
        let sst = Arc::new(builder.build(
            sst_id,
            Some(self.block_cache.clone()),
            self.path_of_sst(sst_id),
        )?);

        // Add the flushed L0 table to the list.
        {
            let mut guard = self.state.write();
            let mut snapshot = guard.as_ref().clone();
            // Remove the memtable from the immutable memtables.
            let mem = snapshot.imm_memtables.pop().unwrap();
            assert_eq!(mem.id(), sst_id);
            // Add L0 table
            if self.compaction_controller.flush_to_l0() {
                // In leveled compaction or no compaction, simply flush to L0
                snapshot.l0_sstables.insert(0, sst_id);
            } else {
                // In tiered compaction, create a new tier
                snapshot.levels.insert(0, (sst_id, vec![sst_id]));
            }
            println!("flushed {}.sst with size={}", sst_id, sst.table_size());
            snapshot.sstables.insert(sst_id, sst);
            // Update the snapshot.
            *guard = Arc::new(snapshot);
        }

        if self.options.enable_wal {
            std::fs::remove_file(self.path_of_wal(sst_id))?;
        }

        self.manifest
            .add_record(&state_lock, ManifestRecord::Flush(sst_id))?;

        self.sync_dir()?;

        Ok(())
    }

    /// Create an iterator over a range of keys.
    pub fn scan(
        &self,
        lower: Bound<&[u8]>,
        upper: Bound<&[u8]>,
    ) -> Result<FusedIterator<LsmIterator>> {
        let snapshot = {
            let guard = self.state.read();
            Arc::clone(&guard)
        }; // drop global lock here

        let mut memtable_iters = Vec::with_capacity(snapshot.imm_memtables.len() + 1);
        memtable_iters.push(Box::new(snapshot.memtable.scan(lower, upper)));
        for memtable in snapshot.imm_memtables.iter() {
            memtable_iters.push(Box::new(memtable.scan(lower, upper)));
        }
        let memtable_iter = MergeIterator::create(memtable_iters);

        let mut table_iters = Vec::with_capacity(snapshot.l0_sstables.len());
        for table_id in snapshot
            .l0_sstables
            .iter()
            .chain(snapshot.levels.iter().map(|(_, files)| files).flatten())
        {
            let table = snapshot.sstables[table_id].clone();
            let iter = match lower {
                Bound::Included(key) => SsTableIterator::create_and_seek_to_key(table, key)?,
                Bound::Excluded(key) => {
                    let mut iter = SsTableIterator::create_and_seek_to_key(table, key)?;
                    if iter.is_valid() && iter.key() == key {
                        iter.next()?;
                    }
                    iter
                }
                Bound::Unbounded => SsTableIterator::create_and_seek_to_first(table)?,
            };

            table_iters.push(Box::new(iter));
        }

        let table_iter = MergeIterator::create(table_iters);

        let iter = TwoMergeIterator::create(memtable_iter, table_iter)?;

        Ok(FusedIterator::new(LsmIterator::new(
            iter,
            map_bound(upper),
        )?))
    }
}