anvil_db 0.2.2

an embedded key-value store
Documentation
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use std::collections::HashSet;
use std::iter::zip;
use std::sync::mpsc::Sender;
use std::sync::{Arc, RwLock};
use std::time::{SystemTime, UNIX_EPOCH};

use crate::compactor::CompactorMessage;
use crate::context::Context;
use crate::kv::{
    JoinedIter, MergedHomogenousIter, TombstonePointReader, TombstoneValue, TryTombstoneScanner,
};
use crate::sst::common::{KeyRangeCmp, RefKeyRange, SstError};
use crate::sst::reader::SstReader;
use crate::sst::reader::SstScanner;
use crate::sst::writer::SstWriteSettings;
use crate::storage::blob_store::BlobStore;

pub(crate) enum TaskCategory {
    Any,
    MajorCompaction,
}

#[derive(Debug)]
pub(crate) enum CompactOrder {
    Minor {
        minor_sst_readers: Vec<SstReader>,
        l0_sst_readers: Vec<SstReader>,
        write_settings: SstWriteSettings,
    },
    Regular {
        lo_sst_readers: Vec<SstReader>,
        hi_sst_readers: Vec<SstReader>,
        target_level_no: usize,
        write_settings: SstWriteSettings,
    },
    Major {
        minor_sst_readers: Vec<SstReader>,
        level_sst_readers: Vec<Vec<SstReader>>,
        target_level_no: usize,
        write_settings: SstWriteSettings,
    },
}

impl CompactOrder {
    // `sst_readers` should be passed in order from oldest to youngest.
    fn minor<I1: Iterator<Item = SstReader>, I2: Iterator<Item = SstReader>>(
        minor_sst_readers: I1,
        l0_sst_readers: I2,
        base_write_settings: SstWriteSettings,
    ) -> Self {
        let minor_sst_readers: Vec<_> = minor_sst_readers.collect();
        let l0_sst_readers: Vec<_> = l0_sst_readers.collect();
        CompactOrder::Minor {
            minor_sst_readers,
            write_settings: base_write_settings,
            l0_sst_readers,
        }
    }

    fn regular<I1: Iterator<Item = SstReader>, I2: Iterator<Item = SstReader>>(
        lo_sst_readers: I1,
        hi_sst_readers: I2,
        target_level_no: usize,
        base_write_settings: SstWriteSettings,
    ) -> Self {
        let lo_sst_readers = lo_sst_readers.collect();
        let hi_sst_readers = hi_sst_readers.collect();
        let write_settings =
            base_write_settings.scale_to_level(target_level_no, LEVEL_BLOW_UP_FACTOR);
        CompactOrder::Regular {
            lo_sst_readers,
            hi_sst_readers,
            target_level_no,
            write_settings,
        }
    }

    fn major<
        I1: Iterator<Item = SstReader>,
        I2: Iterator<Item = SstReader>,
        I3: Iterator<Item = I2>,
    >(
        minor_sst_readers: I1,
        level_sst_readers: I3,
        target_level_no: usize,
        base_write_settings: SstWriteSettings,
    ) -> Self {
        let minor_sst_readers = minor_sst_readers.collect();
        let level_readers = level_sst_readers.map(|level| level.collect()).collect();
        let write_settings =
            base_write_settings.scale_to_level(target_level_no, LEVEL_BLOW_UP_FACTOR);
        CompactOrder::Major {
            minor_sst_readers,
            level_sst_readers: level_readers,
            target_level_no,
            write_settings,
        }
    }
}

/// An SstStore instance is a thread safe wrapper that allows a user to read
/// and write new SST files. It handles caching as well.
pub(crate) trait TabletSstStore:
    Clone + std::fmt::Debug + TombstonePointReader + TryTombstoneScanner
{
    fn recover<B: BlobStore, S: ToString, I: Iterator<Item = S>>(
        blob_store: &B,
        levels: I,
        compactor_tx: Sender<CompactorMessage>,
    ) -> Result<Self, SstError>;
    fn write_settings_ref(&self) -> &SstWriteSettings;
    fn add_minor_sst(&self, sst_reader: SstReader);
    fn request_task(&self, category: &TaskCategory) -> Option<CompactOrder>;
    // Result is either a new SST reader or an error.
    fn handle_finished_task<I: Iterator<Item = SstReader>>(
        &self,
        original_order: &CompactOrder,
        new_readers: I,
    );
}

#[derive(Clone)]
pub(crate) struct SmartTablet {
    write_settings: SstWriteSettings,
    /// Minor sst files, from oldest to youngest.
    ///
    /// What RocksDB calls "level 0" is stored in this collection.
    minors: Arc<RwLock<Vec<SstReader>>>,
    /// The levels of the SST files, ordered from youngest to oldest.
    ///
    /// What RocksDB calls "level 1" is stored at index 0, and so on.
    /// The length of levels is preallocated, and the address the `Arc`s point
    /// to is constant for the lifetime of the table. For that reason, it is
    /// safe to copy across threads.
    /// This means that SST in higher levels represent older data.
    ///
    /// Within each level, the SST files are ordered by their key range.
    /// SSTs within the same level do not have overlapping key range.
    /// Therefore, to read a key from a level, simply iterate over the SST
    /// until it is in one of their range, and then call the point read
    /// function on that SST. If it is not found during the iteration, then it
    /// is not present in the table.
    levels: Arc<Vec<RwLock<Vec<SstReader>>>>,
}

impl std::fmt::Debug for SmartTablet {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let binding = self.minors.read().unwrap();
        let minors = binding.iter().count();
        let levels: Vec<_> = self
            .levels
            .iter()
            .map(|level| {
                let binding = level.read().unwrap();
                binding.iter().count()
                // .map(|r| r.blob_id_ref().to_string())
                // .collect()
            })
            .collect();
        f.debug_struct("SmartTablet")
            .field("minors", &minors)
            .field("levels", &levels.as_slice())
            .finish()
    }
}

const LEVEL_BLOW_UP_FACTOR: usize = 4;
const MAX_NUM_LEVELS: usize = 8;

impl SmartTablet {
    pub(crate) fn new<B: BlobStore, S: ToString, I: Iterator<Item = S>>(
        blob_store: &B,
        levels: I,
        compactor_tx: Sender<CompactorMessage>,
    ) -> Result<Self, SstError> {
        let results: Result<Vec<_>, _> = levels
            .map(|blob_id| SstReader::new(blob_store, &blob_id.to_string(), compactor_tx.clone()))
            .collect();
        let minors = Arc::new(RwLock::new(results?));
        let levels = (0..MAX_NUM_LEVELS)
            .map(|_| RwLock::new(Vec::new()))
            .collect();
        let levels = Arc::new(levels);

        // TODO(t/1392): The default write settings should be configurable.
        let write_settings = SstWriteSettings::default();

        Ok(SmartTablet {
            write_settings,
            minors,
            levels,
        })
    }

    fn sst_snapshot(&self) -> (Vec<SstReader>, Vec<Vec<SstReader>>) {
        (
            self.minors.read().unwrap().clone(),
            (*self.levels)
                .iter()
                .map(|level| level.read().unwrap().clone())
                .collect(),
        )
    }

    fn most_urgent_task(&self) -> Option<CompactOrder> {
        // TODO(t/1393): This should really look at CPU and IO load
        // and adjust based on compaction time.
        // Right now, it just looks at the number of SST and if it is greater
        // than 10, it flips a coin and compacts either the youngest 5 or
        // the oldest 5. If the number is less than 10, it does a major
        // compaction.

        // It is okay if levels is stale. Since the compactor is single
        // threaded, it only means that some minor SST could have been
        // stacked on top during the compaction.

        let (minors, levels) = self.sst_snapshot();

        // prioritize minor compaction
        if minors.len() >= 2 {
            return if levels.is_empty() {
                Some(CompactOrder::minor(
                    minors.into_iter(),
                    vec![].into_iter(),
                    self.write_settings.clone().keep_tombstones(),
                ))
            } else {
                Some(CompactOrder::minor(
                    minors.into_iter(),
                    levels[0].clone().into_iter(),
                    self.write_settings.clone().keep_tombstones(),
                ))
            };
        }

        // Pick a random non-base level.
        let mut source_level = if let Ok(d) = SystemTime::now().duration_since(UNIX_EPOCH) {
            d.as_nanos() as usize % (MAX_NUM_LEVELS - 1)
        } else {
            0
        };

        // If the level is empty, iterate through levels from low to high to
        // find the first non-empty one.
        if levels[source_level].is_empty() {
            if let Some((i, _)) = levels
                .iter()
                .enumerate()
                .take(MAX_NUM_LEVELS - 1)
                .find(|(_, level)| !level.is_empty())
            {
                source_level = i;
            } else if !minors.is_empty() {
                return Some(CompactOrder::major(
                    minors.into_iter(),
                    levels.into_iter().map(|level| level.into_iter()),
                    MAX_NUM_LEVELS - 1,
                    self.write_settings.clone().discard_tombstones(),
                ));
            } else {
                // If all levels are empty, then there is nothing to compact.
                return None;
            }
        }

        let source_level = source_level;

        // Pick the two largest SSTs in the level
        // or just one if there is only one in the level.
        let lo_sst_readers;
        if levels[source_level].len() == 1 {
            lo_sst_readers = vec![levels[source_level][0].clone()];
        } else {
            let mut max_size = 0;
            let mut biggest_pair: Option<(&SstReader, &SstReader)> = None;
            let reader_pairs = zip(
                levels[source_level].iter().take(MAX_NUM_LEVELS - 1),
                levels[source_level].iter().skip(1),
            );
            for (reader_a, reader_b) in reader_pairs {
                let size = reader_a.blob_size() + reader_b.blob_size();
                if size > max_size {
                    max_size = size;
                    biggest_pair = Some((reader_a, reader_b));
                }
            }
            let biggest_pair = biggest_pair.unwrap();
            lo_sst_readers = vec![biggest_pair.0.clone(), biggest_pair.1.clone()];
        }
        let lo_key = lo_sst_readers[0].key_range_ref().start_ref();
        let hi_key = lo_sst_readers[lo_sst_readers.len() - 1]
            .key_range_ref()
            .end_ref();

        let lo_key_range = RefKeyRange::new(lo_key, hi_key);

        let target_level = source_level + 1;
        let mut hi_sst_readers = Vec::with_capacity(levels[target_level].len());
        for sst_reader in &levels[target_level] {
            let cmp = sst_reader.key_range_ref().intersects_range(&lo_key_range);
            match cmp {
                KeyRangeCmp::Less => continue,
                KeyRangeCmp::Greater => break,
                KeyRangeCmp::InRange => {
                    hi_sst_readers.push(sst_reader.clone());
                }
            }
        }

        let mut write_settings = self
            .write_settings
            .clone()
            .scale_to_level(target_level, LEVEL_BLOW_UP_FACTOR);
        if target_level == MAX_NUM_LEVELS - 1 {
            write_settings = write_settings.discard_tombstones();
        }

        Some(CompactOrder::regular(
            lo_sst_readers.into_iter(),
            hi_sst_readers.into_iter(),
            target_level,
            write_settings,
        ))
    }

    fn clear_minors(&self, old_minors: &[SstReader]) {
        let old_minors: HashSet<_> = old_minors.iter().map(|sst| sst.blob_id_ref()).collect();
        let mut minors = self.minors.write().unwrap();
        let mut minor_idx = 0;
        while minor_idx < minors.len() {
            let minor = &minors[minor_idx];
            if !old_minors.contains(&minor.blob_id_ref()) {
                minor_idx += 1;
                continue;
            }
            minors.remove(minor_idx);
        }
    }

    fn renew_level<I: Iterator<Item = SstReader>>(
        &self,
        level_no: usize,
        old_sst_readers: &[SstReader],
        new_sst_readers: I,
    ) {
        let old_sst_blob_ids = old_sst_readers
            .iter()
            .map(|sst| sst.blob_id_ref())
            .collect::<HashSet<_>>();

        let mut level = self.levels[level_no].write().unwrap();
        let mut sst_idx = 0;
        let mut remove_done = false;
        while sst_idx < level.len() {
            let sst = &level[sst_idx];
            if !old_sst_blob_ids.contains(&sst.blob_id_ref()) {
                if remove_done {
                    break;
                }
                sst_idx += 1;
                continue;
            }
            level.remove(sst_idx);
            remove_done = true;
        }
        for sst in new_sst_readers {
            level.insert(sst_idx, sst.clone());
        }
    }

    fn get<Ctx: Context>(&self, ctx: &Ctx, key: &[u8]) -> Result<Option<TombstoneValue>, SstError> {
        let (minors, levels) = self.sst_snapshot();
        for minor in minors.iter().rev() {
            if let Some(value) = minor.get(ctx, key)? {
                return Ok(Some(value));
            }
        }
        for level in levels.iter() {
            for sst in level.iter() {
                match sst.key_range_ref().in_range(key) {
                    KeyRangeCmp::Less => continue,
                    KeyRangeCmp::Greater => break,
                    KeyRangeCmp::InRange => {
                        // fall through
                    }
                }
                if let Some(value) = sst.get(ctx, key)? {
                    return Ok(Some(value));
                }
                break;
            }
        }
        Ok(None)
    }
}

impl TombstonePointReader for SmartTablet {
    type Error = SstError;

    fn get<Ctx: Context>(
        &self,
        ctx: &Ctx,
        key: &[u8],
    ) -> Result<Option<TombstoneValue>, Self::Error> {
        self.get(ctx, key)
    }
}

pub(crate) type SmartTabletIterator<'a, Ctx> = JoinedIter<
    SstError,
    MergedHomogenousIter<SstScanner<'a, Ctx>>,
    MergedHomogenousIter<MergedHomogenousIter<SstScanner<'a, Ctx>>>,
>;

impl TryTombstoneScanner for SmartTablet {
    type Error = SstError;
    type Iter<'a, Ctx>
        = SmartTabletIterator<'a, Ctx>
    where
        Ctx: Context + 'a;

    fn try_scan<'a, Ctx: Context>(
        &self,
        storage_wrapper: &'a Ctx,
    ) -> Result<Self::Iter<'a, Ctx>, Self::Error> {
        let (minors, levels) = self.sst_snapshot();
        let minor_iters = minors
            .into_iter()
            .map(|sst| sst.try_scan(storage_wrapper))
            .collect::<Result<Vec<_>, _>>()?;
        let minor_iter = MergedHomogenousIter::new(minor_iters.into_iter());
        let level_scanners: Vec<_> = levels
            .into_iter()
            .rev()
            .map(|level| {
                level
                    .into_iter()
                    .map(|sst| sst.try_scan(storage_wrapper))
                    .collect::<Result<Vec<_>, _>>()
            })
            .collect::<Result<Vec<_>, _>>()?;
        let merged_level_scanners = level_scanners
            .into_iter()
            .map(|scanners| MergedHomogenousIter::new(scanners.into_iter()));
        let level_iter = MergedHomogenousIter::new(merged_level_scanners.into_iter());
        let scanner = JoinedIter::new(minor_iter, level_iter);
        Ok(scanner)
    }
}

unsafe impl Send for SmartTablet {}

impl TabletSstStore for SmartTablet {
    fn recover<B: BlobStore, S: ToString, I: Iterator<Item = S>>(
        blob_store_ref: &B,
        levels: I,
        compactor_tx: Sender<CompactorMessage>,
    ) -> Result<Self, SstError> {
        SmartTablet::new(blob_store_ref, levels, compactor_tx)
    }

    fn request_task(&self, category: &TaskCategory) -> Option<CompactOrder> {
        match category {
            TaskCategory::Any => self.most_urgent_task(),
            TaskCategory::MajorCompaction => {
                let (minors, levels) = self.sst_snapshot();
                let level_sst_readers = levels.into_iter().map(|level| level.into_iter());
                Some(CompactOrder::major(
                    minors.into_iter(),
                    level_sst_readers,
                    MAX_NUM_LEVELS - 1,
                    self.write_settings.clone().discard_tombstones(),
                ))
            }
        }
    }

    fn handle_finished_task<I: Iterator<Item = SstReader>>(
        &self,
        original_order: &CompactOrder,
        new_readers: I,
    ) {
        // TODO(t/1397): This is not safe if their are multiple compactors.
        // The method `clear_minors` will be fine (if slow) if their are
        // multiple compactor threads, but the `renew_level` method assumes the
        // list of SST in a level is the same as when a compaction was
        // initiated.
        match original_order {
            CompactOrder::Minor {
                minor_sst_readers,
                l0_sst_readers,
                ..
            } => {
                self.clear_minors(minor_sst_readers.as_slice());
                self.renew_level(0, l0_sst_readers.as_slice(), new_readers);
            }
            CompactOrder::Regular {
                lo_sst_readers,
                hi_sst_readers,
                target_level_no,
                ..
            } => {
                self.renew_level(*target_level_no, hi_sst_readers, new_readers);
                self.renew_level(*target_level_no - 1, lo_sst_readers, vec![].into_iter());
            }
            CompactOrder::Major {
                minor_sst_readers,
                level_sst_readers,
                target_level_no,
                ..
            } => {
                debug_assert_eq!(*target_level_no, MAX_NUM_LEVELS - 1);
                debug_assert_eq!(level_sst_readers.len(), MAX_NUM_LEVELS);
                self.renew_level(
                    MAX_NUM_LEVELS - 1,
                    &level_sst_readers[MAX_NUM_LEVELS - 1],
                    new_readers,
                );
                for level_no in (0..MAX_NUM_LEVELS - 1).rev() {
                    self.renew_level(level_no, &level_sst_readers[level_no], vec![].into_iter());
                }
                self.clear_minors(minor_sst_readers.as_slice());
            }
        }
    }

    fn write_settings_ref(&self) -> &SstWriteSettings {
        &self.write_settings
    }

    fn add_minor_sst(&self, sst_reader: SstReader) {
        self.minors.write().unwrap().push(sst_reader);
    }
}

#[cfg(test)]
mod test {

    use std::sync::atomic::AtomicBool;
    use std::sync::atomic::AtomicU32;
    use std::sync::mpsc::channel;
    use std::time::Duration;

    use super::*;
    use crate::compactor::Compactor;
    use crate::compactor::CompactorSettings;
    use crate::context::SimpleContext;
    use crate::helpful_macros::{clone, spawn, unwrap};
    use crate::kv::TombstonePair;
    use crate::logging::debug;
    use crate::logging::error;
    use crate::logging::info;
    use crate::logging::ArchiveLogger;
    use crate::logging::DefaultLogger;
    use crate::logging::FixPrefixLogger;
    use crate::logging::Logger;
    use crate::sst::block_cache::cache::LruCache;
    use crate::sst::block_cache::cache::PolicyHolder;
    use crate::sst::block_cache::BlockCache;
    use crate::storage::blob_store::InMemoryBlobStore;

    type SuperSimpleContext<L> = SimpleContext<InMemoryBlobStore, PolicyHolder<LruCache>, L>;

    fn new_test_sst_store(
        compactor_tx: Option<Sender<CompactorMessage>>,
    ) -> (SuperSimpleContext<DefaultLogger>, SmartTablet) {
        let logger = DefaultLogger::default();
        make_sst_store_from_logger(compactor_tx, logger)
    }
    fn make_sst_store_from_logger<L: Logger>(
        compactor_tx: Option<Sender<CompactorMessage>>,
        logger: L,
    ) -> (SuperSimpleContext<L>, SmartTablet) {
        let blob_store = InMemoryBlobStore::new();
        let ctx = SimpleContext::from((
            blob_store,
            PolicyHolder::<LruCache>::with_capacity(32),
            logger,
        ));
        let levels: Vec<String> = Vec::new();
        if let Some(compactor_tx) = compactor_tx {
            return (
                ctx.clone(),
                SmartTablet::new(ctx.blob_store_ref(), levels.into_iter(), compactor_tx).unwrap(),
            );
        }
        let (compactor_tx, compactor_rx) = channel();
        spawn!(move || {
            while let Ok(message) = compactor_rx.recv() {
                debug!(&(), "message: {:?}", message);
            }
        });
        (
            ctx.clone(),
            SmartTablet::new(ctx.blob_store_ref(), levels.into_iter(), compactor_tx).unwrap(),
        )
    }

    fn run_minor_compaction<Ctx: Context, T: TabletSstStore, I: Iterator<Item = TombstonePair>>(
        ctx: &Ctx,
        sst_store: T,
        pairs: I,
    ) {
        let mut compactor = Compactor::one_off(sst_store);
        unwrap!(compactor.minor_compact(ctx, pairs));
    }

    #[test]
    fn test_basic_minor_compact() {
        let top: u64 = 1_024;

        let pairs: Vec<TombstonePair> = (0..top)
            .map(|i| {
                let key_bytes = i.to_be_bytes().to_vec();
                if i % 2 == 0 {
                    TombstonePair::new(key_bytes, (i * i).to_be_bytes().to_vec())
                } else {
                    TombstonePair::deletion_marker(key_bytes)
                }
            })
            .collect();

        let (ctx, sst_store) = new_test_sst_store(None);
        run_minor_compaction(&ctx, sst_store.clone(), pairs.into_iter());

        for i in 0..top {
            let key_bytes = i.to_be_bytes().to_vec();
            let value = sst_store.get(&ctx, &key_bytes).unwrap().unwrap();
            if i % 2 == 0 {
                assert!(
                    value.as_ref().is_some(),
                    "could find read value at key {key_bytes:?}; index {i}",
                );
                assert_eq!(*value.as_ref().unwrap(), (i * i).to_be_bytes().to_vec());
            } else {
                assert!(value.as_ref().is_none());
            }

            let key_bytes = (top + i).to_be_bytes().to_vec();
            assert!(sst_store.get(&ctx, &key_bytes).unwrap().is_none());
        }
    }

    fn complex_test_values(top: u64) -> Vec<(Vec<TombstonePair>, Vec<Option<TombstoneValue>>)> {
        let mut ret: Vec<(Vec<TombstonePair>, Vec<Option<TombstoneValue>>)> = Vec::with_capacity(4);

        // BATCH 0: evens are squares, odds are tombstones
        let size_1 = top / 8;
        let wal_values = (0..size_1)
            .map(|i| {
                let key_bytes = i.to_be_bytes().to_vec();
                if i % 2 == 0 {
                    TombstonePair::new(key_bytes, (i * i).to_be_bytes().to_vec())
                } else {
                    TombstonePair::deletion_marker(key_bytes)
                }
            })
            .collect();
        let mut expected_values: Vec<Option<TombstoneValue>> = vec![None; top as usize];
        for i in 0..size_1 {
            expected_values[i as usize] = if i % 2 == 0 {
                Some(TombstoneValue::Value((i * i).to_be_bytes().to_vec()))
            } else {
                Some(TombstoneValue::Tombstone)
            };
        }
        ret.push((wal_values, expected_values.clone()));

        // BATCH 1: every other even is half the square
        let size_2 = top / 4;
        let wal_values = (0..(size_2 / 4))
            .map(|i| {
                let j = 4 * i;
                let key_bytes = j.to_be_bytes().to_vec();
                let value_bytes = (j * j / 2).to_be_bytes().to_vec();
                TombstonePair::new(key_bytes, value_bytes)
            })
            .collect();
        for i in 0..size_2 {
            if i % 4 != 0 {
                continue;
            }
            expected_values[i as usize] =
                Some(TombstoneValue::Value((i * i / 2).to_be_bytes().to_vec()));
        }
        ret.push((wal_values, expected_values.clone()));

        // BATCH 2: every third value is set to 42
        let size_3 = top / 2;
        let wal_values = (0..(size_3 / 3))
            .map(|i| {
                let j = 3 * i;
                let key_bytes = j.to_be_bytes().to_vec();
                let value_bytes = 42u64.to_be_bytes().to_vec();
                TombstonePair::new(key_bytes, value_bytes)
            })
            .collect();
        for i in 0..(3 * (size_3 / 3)) {
            if i % 3 != 0 {
                continue;
            }
            expected_values[i as usize] = Some(TombstoneValue::Value(42u64.to_be_bytes().to_vec()));
        }
        ret.push((wal_values, expected_values.clone()));

        // BATCH 3: every 5th value is deleted
        let size_4 = top;
        let wal_values = (0..(size_4 / 5))
            .map(|i| {
                let j = 5 * i;
                let key_bytes = j.to_be_bytes().to_vec();
                TombstonePair::deletion_marker(key_bytes)
            })
            .collect();
        for i in 0..(5 * (size_4 / 5)) {
            if i % 5 != 0 {
                continue;
            }
            expected_values[i as usize] = Some(TombstoneValue::Tombstone);
        }
        ret.push((wal_values, expected_values));

        ret
    }

    #[test]
    fn test_multiple_minor_compact() {
        let top: u64 = 1_024;

        let (ctx, sst_store) = new_test_sst_store(None);

        fn check_values<Ctx: Context>(
            store: &SmartTablet,
            ctx: &Ctx,
            top: u64,
            prime: u64,
            expected_values: &[Option<TombstoneValue>],
        ) {
            let mut all_checked = vec![false; top as usize];
            let mut idx = 0_u64;
            for _ in 0..top {
                idx += prime;
                idx %= top;
                all_checked[idx as usize] = true;
                let key_bytes = idx.to_be_bytes().to_vec();
                if expected_values[idx as usize].is_none() {
                    assert!(store.get(ctx, &key_bytes).unwrap().is_none());
                    continue;
                }
                let t_value = store.get(ctx, &key_bytes).unwrap().unwrap();
                let t_expected = expected_values[idx as usize].as_ref().unwrap().clone();
                if t_expected.as_ref().is_none() {
                    assert!(t_value.as_ref().is_none());
                    continue;
                }
                let expected: Vec<u8> = t_expected.as_ref().unwrap().clone();
                assert_eq!(*t_value.as_ref().unwrap(), expected);
            }
            assert!(all_checked.iter().all(|&b| b));
        }

        let primes = [1009, 1013, 1049, 2539];
        let test_values = complex_test_values(top);

        for (i, (wal_values, expected_values)) in test_values.into_iter().enumerate() {
            run_minor_compaction(&ctx, sst_store.clone(), wal_values.into_iter());
            check_values(&sst_store, &ctx, top, primes[i], &expected_values);
        }
    }

    #[test]
    fn test_multiple_scans() {
        let top = 1024;

        let (compactor_tx, _compactor_rx) = channel();
        let (ctx, sst_store) = new_test_sst_store(Some(compactor_tx));

        let test_values = complex_test_values(top);
        for (wal_values, raw_expected_values) in test_values.into_iter() {
            run_minor_compaction(&ctx, sst_store.clone(), wal_values.into_iter());
            let expected_values = raw_expected_values
                .into_iter()
                .enumerate()
                .filter_map(|(i, v)| {
                    v.as_ref()?;
                    let key_bytes = i.to_be_bytes().to_vec();
                    let value = v.unwrap();
                    Some((key_bytes, value))
                })
                .collect::<Vec<(Vec<u8>, TombstoneValue)>>();

            let iter = unwrap!(sst_store.try_scan(&ctx));
            for (idx, result) in iter.enumerate() {
                let found_pair = result.unwrap();
                let (key_bytes, expected_value) = expected_values[idx].clone();
                assert_eq!(found_pair.key_ref(), &key_bytes);
                assert_eq!(found_pair.value_ref().as_ref(), expected_value.as_ref());
            }
        }
    }

    fn level_updates_are_atomic_inner(thread_id: usize) -> Result<(), ArchiveLogger> {
        // Time to beat is 8 sec with top = 1024 ** 2 / 8
        let logger = ArchiveLogger::new(&format!("lg-{thread_id}"));

        let top = 1024 * 1024 / 8;
        let n_partitions = 32;
        let n_scanners = 8;

        info!(
            &logger,
            "running level_updates_are_atomic_inner thread_id: thread_id = {thread_id} ; top = \
             {top} ; n_partitions = {n_partitions} ; n_scanners = {n_scanners}"
        );

        let (compactor_tx, compactor_rx) = channel();
        let (ctx, sst_store) =
            make_sst_store_from_logger(Some(compactor_tx.clone()), logger.clone());

        info!(&logger, "made ctx, sst_store, and compactor_tx");

        let compactor = Compactor::new(
            sst_store.clone(),
            CompactorSettings::default(),
            compactor_tx.clone(),
            compactor_rx,
            0,
        );
        let bg_ctx = clone!(ctx);
        {
            let logger = logger.clone();
            spawn!(move || {
                info!(&logger, "starting compactor thread");
                compactor.run(&bg_ctx)
            });
        }

        info!(&logger, "compactor running in separate thread");

        let test_values = complex_test_values(top);
        for (batch, (wal_values, raw_expected_values)) in
            test_values.into_iter().enumerate().take(3)
        {
            info!(&logger, "setting up batch number: {batch}");
            let mut seen_values = HashSet::new();
            for r in 0..n_partitions {
                info!(
                    &logger,
                    "running minor compaction for partition number {r} in batch number {batch}"
                );
                let pairs: std::iter::Cloned<
                    std::iter::StepBy<std::iter::Skip<std::slice::Iter<'_, TombstonePair>>>,
                > = wal_values.iter().skip(r).step_by(n_partitions).cloned();
                run_minor_compaction(&ctx, sst_store.clone(), pairs.clone());
                for pair in pairs {
                    seen_values.insert(pair.key_ref().to_vec());
                }
            }
            for wal_value in wal_values.iter() {
                if !seen_values.contains(wal_value.key_ref()) {
                    error!(
                        &logger,
                        "wal value missing: batch_no = {batch} ; key = {key:?}",
                        key = wal_value.key_ref()
                    );
                    return Err(logger.clone());
                }
            }
            if seen_values.len() != wal_values.len() {
                error!(
                    &logger,
                    "seen values: {seen_values:?} ; wal values: {wal_values:?}"
                );
                return Err(logger.clone());
            }
            let expected_values = raw_expected_values
                .into_iter()
                .enumerate()
                .filter_map(|(i, v)| {
                    let key_bytes = i.to_be_bytes().to_vec();
                    let value = v.as_ref()?.as_ref()?.clone();
                    Some((key_bytes, value))
                })
                .collect::<Vec<(Vec<u8>, Vec<u8>)>>();
            let logger = logger.clone();
            let num_errors = Arc::new(AtomicU32::new(0));
            std::thread::sleep(Duration::from_millis(5000));
            // let p_expected_values: Vec<_> = expected_values
            //     .clone()
            //     .into_iter()
            //     .filter_map(|(key, value)| value.as_ref().map(|value| (key,
            // value.clone())))     .collect();
            std::thread::scope(|s| {
                let mut children = Vec::with_capacity(n_scanners);
                for sub_thread_id in 0..n_scanners {
                    let sst_store = sst_store.clone();
                    let ctx = ctx.clone();
                    let p_expected_values = expected_values.clone();
                    let logger = logger.clone();
                    let num_errors = num_errors.clone();
                    children.push(s.spawn(move || {
                        let iter = sst_store.try_scan(&ctx).unwrap();
                        info!(
                            &logger,
                            "starting thread_id: {thread_id}-{sub_thread_id}, batch: {batch}"
                        );
                        let real_pairs: Vec<_> = iter
                            .map(|result| match result {
                                Ok(ok) => ok,
                                Err(err) => {
                                    panic!("Error scanning: {err:?}",);
                                }
                            })
                            .filter_map(|pair| {
                                pair.value_ref()
                                    .as_ref()
                                    .map(|value| (pair.key_ref().to_vec(), value.clone()))
                            })
                            .collect();
                        for (idx, (found_key, found_value)) in real_pairs.iter().enumerate() {
                            let (expected_key, expected_value) = p_expected_values[idx].clone();

                            if *found_key != expected_key {
                                error!(
                                    &logger,
                                    "found_key: {found_key:?}\nexpected_key: {expected_key:?}\n \
                                     thread_id: {thread_id}-{sub_thread_id}, idx: {idx}, batch: \
                                     {batch}",
                                );
                                num_errors.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
                                return;
                            }

                            if *found_value != expected_value {
                                error!(
                                    &logger,
                                    "found_key: {found_key:?}\nexpected_key: {expected_key:?}\n \
                                     found_value: {found_value:?}\nexpected_value: \
                                     {expected_value:?}\nthread_id: {thread_id}-{sub_thread_id}, \
                                     idx: {idx}, batch: {batch}",
                                );
                                num_errors.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
                                return;
                            }
                        }
                        info!(
                            &logger,
                            "ending thread_id: {thread_id}-{sub_thread_id}, batch: {batch}"
                        );
                    }));
                }
                for (sub_thread_id, child) in children.into_iter().enumerate() {
                    if child.join().is_err() {
                        error!(
                            &logger,
                            "Error joining thread_id: {thread_id}-{sub_thread_id}, batch: {batch}"
                        );
                        num_errors.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
                        return;
                    }
                }
            });
            if num_errors.load(std::sync::atomic::Ordering::SeqCst) > 0 {
                error!(
                    &logger,
                    "thread_id: {thread_id}, batch: {batch}, num_errors: {}",
                    num_errors.load(std::sync::atomic::Ordering::SeqCst)
                );
                return Err(logger.clone());
            }
        }

        if let Err(err) = compactor_tx.send(CompactorMessage::Shutdown) {
            error!(
                &logger,
                "Error sending shutdown message to compactor: {err:?}",
            );
            return Err(logger.clone());
        }
        Ok(())
    }

    #[test]
    fn test_level_updates_are_atomic() {
        let top = 4;
        let start = Arc::new(AtomicBool::new(false));
        let mut handles = Vec::with_capacity(top);
        let (logger_tx, logger_rx) = channel();
        for thread_id in 0..top {
            let start = start.clone();
            let logger_tx = logger_tx.clone();
            handles.push(spawn!(move || {
                while !start.load(std::sync::atomic::Ordering::SeqCst) {
                    std::thread::yield_now();
                }
                let _ = logger_tx.send(level_updates_are_atomic_inner(thread_id));
            }));
        }
        start.store(true, std::sync::atomic::Ordering::SeqCst);
        for _ in 0..top {
            let result = unwrap!(logger_rx.recv());
            if let Err(logger) = result {
                let inner = FixPrefixLogger::new("[HISTORY]");
                for line in logger.history_ref() {
                    debug!(&inner, "{line}");
                }
                panic!();
            }
        }
        for handle in handles {
            if let Err(err) = handle.join() {
                panic!("Error joining thread: {err:?}",);
            }
        }
    }
}