stewball/stores/

cache.rs

use arrayvec::ArrayVec;
use bytes::{BufMut, Bytes, BytesMut};
use hashbrown::HashMap;
use ordinary_config::{CacheLimits, StoredCache as StoredCacheConfig, StoredCachePolicy};
use parking_lot::Mutex;
use saferlmdb::{
    self as lmdb, Database, DatabaseOptions, Environment, ReadTransaction, WriteTransaction, put,
};
use std::cmp::Ordering;
use std::collections::{BTreeMap, BTreeSet, BinaryHeap, VecDeque};
use std::error::Error;
use std::sync::Arc;
use std::time::{Duration, SystemTime};
use tracing::instrument;

pub enum CacheRead {
    Template,
    Action,
    Integration,
}

impl CacheRead {
    fn as_u8(&self) -> u8 {
        match self {
            CacheRead::Action => 1,
            CacheRead::Template => 2,
            CacheRead::Integration => 3,
        }
    }
}

pub enum CacheWrite<'a> {
    /// `(etag, last_modified, blob)`
    Template(&'a str, &'a str, &'a Bytes),
    Action,
    Integration,
}

impl CacheWrite<'_> {
    fn as_u8(&self) -> u8 {
        match self {
            CacheWrite::Action => 1,
            CacheWrite::Template(..) => 2,
            CacheWrite::Integration => 3,
        }
    }
}

#[derive(Debug)]
pub enum CacheCompression {
    Gzip,
    Zstd { level: u8 },
    Brotli,
    Deflate,
}

impl CacheCompression {
    fn as_u8(&self) -> u8 {
        match self {
            CacheCompression::Gzip => 1,
            CacheCompression::Zstd { level: _ } => 2,
            CacheCompression::Brotli => 3,
            CacheCompression::Deflate => 4,
        }
    }

    #[must_use]
    pub fn as_char(&self) -> char {
        match self {
            CacheCompression::Gzip => '1',
            CacheCompression::Zstd { level: _ } => '2',
            CacheCompression::Brotli => '3',
            CacheCompression::Deflate => '4',
        }
    }

    #[must_use]
    pub fn as_str(&self) -> &'static str {
        match self {
            CacheCompression::Gzip => "gzip",
            CacheCompression::Zstd { level: _ } => "zstd",
            CacheCompression::Brotli => "br",
            CacheCompression::Deflate => "deflate",
        }
    }
}

#[derive(Debug, Clone, Eq, Hash, PartialEq)]
pub enum CacheDependency {
    Content,
    Model([u8; 16]),
}

// todo: consider including time-to-render in the weights as well.
/// `(total_hits, last_hit, size, addr, idx)`
#[derive(Debug, Hash, PartialEq, Eq, Default)]
pub struct FRsEvictionCandidate {
    /// `(hits, eq_threshold)`
    total_hits: (i64, i64),
    /// `(timestamp, eq_threshold)`
    last_hit: (i64, i64),
    size: usize,
    address: String,
    index: usize,
}

impl PartialOrd for FRsEvictionCandidate {
    #[inline]
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }

    #[inline]
    fn lt(&self, other: &Self) -> bool {
        let Some(th_delta) = other.total_hits.0.checked_sub(self.total_hits.0) else {
            return false;
        };

        if th_delta.abs() > self.total_hits.1 {
            return self.total_hits.0 >= other.total_hits.0;
        }

        let Some(lh_delta) = other.last_hit.0.checked_sub(self.last_hit.0) else {
            return false;
        };

        if lh_delta.abs() > self.last_hit.1 {
            return self.last_hit.0 >= other.last_hit.0;
        }

        self.size < other.size
    }
    #[inline]
    fn le(&self, other: &Self) -> bool {
        let Some(th_delta) = other.total_hits.0.checked_sub(self.total_hits.0) else {
            return false;
        };

        if th_delta.abs() > self.total_hits.1 {
            return self.total_hits.0 > other.total_hits.0;
        }

        let Some(lh_delta) = other.last_hit.0.checked_sub(self.last_hit.0) else {
            return false;
        };

        if lh_delta.abs() > self.last_hit.1 {
            return self.last_hit.0 > other.last_hit.0;
        }

        self.size <= other.size
    }
    #[inline]
    fn gt(&self, other: &Self) -> bool {
        let Some(th_delta) = other.total_hits.0.checked_sub(self.total_hits.0) else {
            return false;
        };

        if th_delta.abs() > self.total_hits.1 {
            return self.total_hits.0 <= other.total_hits.0;
        }

        let Some(lh_delta) = other.last_hit.0.checked_sub(self.last_hit.0) else {
            return false;
        };

        if lh_delta.abs() > self.last_hit.1 {
            return self.last_hit.0 <= other.last_hit.0;
        }

        self.size > other.size
    }
    #[inline]
    fn ge(&self, other: &Self) -> bool {
        let Some(th_delta) = other.total_hits.0.checked_sub(self.total_hits.0) else {
            return false;
        };

        if th_delta.abs() > self.total_hits.1 {
            return self.total_hits.0 < other.total_hits.0;
        }

        let Some(lh_delta) = other.last_hit.0.checked_sub(self.last_hit.0) else {
            return false;
        };

        if lh_delta.abs() > self.last_hit.1 {
            return self.last_hit.0 < other.last_hit.0;
        }

        self.size >= other.size
    }
}

impl Ord for FRsEvictionCandidate {
    #[inline]
    fn cmp(&self, other: &Self) -> Ordering {
        let Some(th_delta) = other.total_hits.0.checked_sub(self.total_hits.0) else {
            return Ordering::Equal;
        };

        if th_delta.abs() > self.total_hits.1 {
            return other.total_hits.0.cmp(&self.total_hits.0);
        }

        let Some(lh_delta) = other.last_hit.0.checked_sub(self.last_hit.0) else {
            return Ordering::Equal;
        };

        if lh_delta.abs() > self.last_hit.1 {
            return other.last_hit.0.cmp(&self.last_hit.0);
        }

        self.size.cmp(&other.size)
    }
}

#[derive(Debug)]
struct AddressDetails {
    /// what compression was used when stored
    compression: u8,

    /// unix timestamp of when the record was first stored
    stored_at: u64,

    /// unix timestamp of last time this record was hit
    last_hit: u64,

    /// total record size in bytes
    size: usize,

    /// distribution of hits within the sync window,
    /// chunked by the min clean interval.
    ///
    /// always increment `.last()` on hit, and always unshift
    /// `.first()` on clean.
    ///
    /// number of elements in the Vec are `frequency_window/avg(clean_interval.0, clean_interval.1)`
    hit_distribution: VecDeque<u64>,

    dependencies: Vec<CacheDependency>,
}

/// `(cache_kind, idx) -> (total_size, total_count, { [addr] -> details[] }`
type AddressesMap =
    Arc<Mutex<HashMap<(u8, u8), (usize, usize, BTreeMap<String, ArrayVec<AddressDetails, 5>>)>>>;

/// Max-heap
type EvictionQueue = Arc<Mutex<BinaryHeap<FRsEvictionCandidate>>>;

/// `(cache_kind, service_idx, addr, compression_idx)`
type DependencyMap = Arc<Mutex<HashMap<CacheDependency, BTreeSet<(u8, u8, String, u8)>>>>;

pub struct CacheStore {
    pub limits: CacheLimits,
    env: Arc<Environment>,

    /// stores cached results
    cache_db: Arc<Database<'static>>,

    log_size: bool,

    addresses_map: AddressesMap,
    eviction_queue: EvictionQueue,

    dependency_map: DependencyMap,
}

impl CacheStore {
    #[allow(clippy::too_many_lines, clippy::missing_panics_doc)]
    pub fn new(
        limits: CacheLimits,
        env: &Arc<Environment>,
        log_size: bool,
    ) -> Result<Self, Box<dyn Error>> {
        // todo: get from `cache_db` on startup
        let eviction_queue = BinaryHeap::new();

        let mut addresses_map = HashMap::new();
        let mut dependency_map = HashMap::new();

        let cache_db = Arc::new(Database::open(
            env.clone(),
            Some("cache"),
            &DatabaseOptions::new(lmdb::db::Flags::CREATE),
        )?);

        let txn = ReadTransaction::new(env.clone())?;
        let access = txn.access();

        let mut cursor = txn.cursor(cache_db.clone())?;

        if let Ok((k, v)) = cursor.seek_range_k::<[u8], [u8]>(&access, &[0u8]) {
            let mut key = k;
            let mut value = v;

            loop {
                if key.len() == 3 && key[0] == 0 {
                    if let Ok(decompressed) = zstd::stream::decode_all(value)
                        && !decompressed.is_empty()
                    {
                        let root = flexbuffers::Reader::get_root(decompressed.as_slice())?;

                        let addresses_vec = root.as_vector();

                        let mut inner_addresses_map = BTreeMap::new();

                        let mut total_size = 0;
                        let mut total_count = 0;

                        for address in &addresses_vec {
                            let address_vec = address.as_vector();
                            let address = address_vec.idx(0).as_str();

                            let mut variants = ArrayVec::<AddressDetails, 5>::new();

                            for variant in &address_vec.idx(1).as_vector() {
                                let variant_vec = variant.as_vector();

                                let compression = variant_vec.idx(0).as_u8();

                                tracing::debug!(
                                    kind = key[1],
                                    i = key[2],
                                    address,
                                    compression,
                                    "restoring from sync"
                                );

                                let last_hit = variant_vec.idx(1).as_u64();

                                let mut hit_distribution = VecDeque::new();

                                for hit in &variant_vec.idx(2).as_vector() {
                                    hit_distribution.push_back(hit.as_u64());
                                }

                                let mut lookup = BytesMut::new();

                                lookup.put(&key[1..3]);
                                lookup.put(address.as_bytes());
                                lookup.put_u8(compression);

                                if let Ok(val) =
                                    access.get::<[u8], [u8]>(&cache_db, lookup.as_ref())
                                {
                                    Self::process_details(
                                        key[1],
                                        key[2],
                                        address,
                                        &mut total_size,
                                        &mut total_count,
                                        &mut variants,
                                        compression,
                                        last_hit,
                                        hit_distribution,
                                        &lookup,
                                        val,
                                        false,
                                        &mut dependency_map,
                                    )?;
                                }
                            }

                            inner_addresses_map.insert(address.to_owned(), variants);
                        }

                        addresses_map.insert(
                            (key[1], key[2]),
                            (total_size, total_count, inner_addresses_map),
                        );
                    }
                } else {
                    let (total_size, total_count, addresses) = addresses_map
                        .entry((key[0], key[1]))
                        .or_insert((0, 0, BTreeMap::new()));

                    let address = std::str::from_utf8(&key[2..key.len() - 1])?;
                    let compression = *key.last().expect("length is not greater than 1");

                    let variants = addresses
                        .entry(address.to_owned())
                        .or_insert(ArrayVec::new());

                    if !variants.iter().any(|v| v.compression == compression) {
                        tracing::debug!(
                            kind = key[0],
                            i = key[1],
                            address,
                            compression,
                            "restoring from cache"
                        );

                        Self::process_details(
                            key[0],
                            key[1],
                            address,
                            total_size,
                            total_count,
                            variants,
                            compression,
                            0,
                            VecDeque::new(),
                            key,
                            value,
                            true,
                            &mut dependency_map,
                        )?;
                    }
                }

                if let Ok((k, v)) = cursor.next::<[u8], [u8]>(&access) {
                    key = k;
                    value = v;
                } else {
                    break;
                }
            }
        }

        Ok(Self {
            limits,
            env: env.clone(),
            cache_db,
            log_size,
            addresses_map: Arc::new(Mutex::new(addresses_map)),
            eviction_queue: Arc::new(Mutex::new(eviction_queue)),
            dependency_map: Arc::new(Mutex::new(dependency_map)),
        })
    }

    #[allow(clippy::too_many_arguments)]
    fn process_details(
        artifact_kind: u8,
        idx: u8,
        address: &str,
        total_size: &mut usize,
        total_count: &mut usize,
        variants: &mut ArrayVec<AddressDetails, 5>,
        compression: u8,
        last_hit: u64,
        hit_distribution: VecDeque<u64>,
        lookup: &[u8],
        val: &[u8],
        last_hit_is_stored_at: bool,
        dependency_map: &mut HashMap<CacheDependency, BTreeSet<(u8, u8, String, u8)>>,
    ) -> Result<(), Box<dyn Error>> {
        let root = flexbuffers::Reader::get_root(val)?;
        let internal_vec = root.as_vector().idx(0).as_vector();

        let mut dependencies = vec![];

        for dep in &internal_vec.idx(1).as_vector() {
            let dep_vec = dep.as_vector();

            let kind = dep_vec.idx(0).as_u8();

            if kind == 0 {
                dependencies.push(CacheDependency::Content);
                dependency_map
                    .entry(CacheDependency::Content)
                    .or_default()
                    .insert((artifact_kind, idx, address.to_owned(), compression));
            } else if kind == 1 {
                let uuid: [u8; 16] = dep_vec.idx(1).as_blob().0.try_into()?;
                dependencies.push(CacheDependency::Model(uuid));
                dependency_map
                    .entry(CacheDependency::Model(uuid))
                    .or_default()
                    .insert((artifact_kind, idx, address.to_owned(), compression));
            }
        }

        let size = lookup.len() + val.len();

        *total_size += size;
        *total_count += 1;

        variants.push(AddressDetails {
            compression,
            last_hit: if last_hit_is_stored_at {
                internal_vec.idx(0).as_u64()
            } else {
                last_hit
            },
            hit_distribution,

            size,
            stored_at: internal_vec.idx(0).as_u64(),
            dependencies,
        });
        Ok(())
    }

    /// Check the `cache_db` for a hit; returns `Err()` if not.
    #[allow(clippy::type_complexity)]
    #[instrument(skip(self, cache_kind, compression, idx, addr), err)]
    pub fn check<'a>(
        &self,
        cache_kind: &CacheRead,
        compression: &'a ArrayVec<CacheCompression, 4>,
        idx: u8,
        addr: &str,
    ) -> Result<Option<(Bytes, Option<&'a CacheCompression>)>, Box<dyn Error>> {
        let mut key = BytesMut::new();

        let addr_bytes = addr.as_bytes();
        let base_key_len = addr_bytes.len() + 2;

        key.put_u8(cache_kind.as_u8());
        key.put_u8(idx);
        key.put(addr_bytes);

        let txn = ReadTransaction::new(self.env.clone())?;
        let access = txn.access();

        for compression in compression {
            key.truncate(base_key_len);
            key.put_u8(compression.as_u8());

            if let Ok(result) = access.get::<[u8], [u8]>(&self.cache_db, key.as_ref()) {
                let mut lock = self.addresses_map.lock();

                if let Some((_total_size, _total_count, addresses)) =
                    lock.get_mut(&(cache_kind.as_u8(), idx))
                    && let Some(details) = addresses.get_mut(addr)
                    && let Some(details) = details
                        .iter_mut()
                        .find(|v| v.compression == compression.as_u8())
                {
                    details.last_hit = SystemTime::now()
                        .duration_since(SystemTime::UNIX_EPOCH)?
                        .as_secs();

                    if let Some(back) = details.hit_distribution.back_mut() {
                        *back += 1;
                    }
                }

                drop(lock);

                if self.log_size {
                    tracing::info!(size = %bytesize::ByteSize((key.len() + result.len()) as u64).display().si_short(), compressed = compression.as_str(), "hit");
                } else {
                    tracing::info!(compressed = compression.as_str(), "hit");
                }
                return Ok(Some((Bytes::copy_from_slice(result), Some(compression))));
            }
        }

        key.truncate(base_key_len);
        key.put_u8(0);

        if let Ok(result) = access.get::<[u8], [u8]>(&self.cache_db, key.as_ref()) {
            let mut lock = self.addresses_map.lock();

            if let Some((_total_size, _total_count, addresses)) =
                lock.get_mut(&(cache_kind.as_u8(), idx))
                && let Some(details) = addresses.get_mut(addr)
                && let Some(details) = details.iter_mut().find(|v| v.compression == 0)
            {
                details.last_hit = SystemTime::now()
                    .duration_since(SystemTime::UNIX_EPOCH)?
                    .as_secs();

                if let Some(back) = details.hit_distribution.back_mut() {
                    *back += 1;
                }
            }

            drop(lock);

            if self.log_size {
                tracing::info!(size = %bytesize::ByteSize((key.len() + result.len()) as u64).display().si_short(), compressed = "false", "hit");
            } else {
                tracing::info!(compressed = "false", "hit");
            }
            Ok(Some((Bytes::copy_from_slice(result), None)))
        } else {
            tracing::info!("miss");
            Ok(None)
        }
    }

    /// Caches item for kind and index at specified addr.
    #[allow(
        clippy::too_many_lines,
        clippy::too_many_arguments,
        clippy::similar_names
    )]
    #[instrument(
        skip(self, cache_kind, compression, idx, config, addr, dependencies),
        err
    )]
    pub fn write(
        &self,
        cache_kind: CacheWrite,
        compression: Option<&CacheCompression>,
        idx: u8,
        config: &StoredCacheConfig,
        addr: &str,
        dependencies: Vec<CacheDependency>,
    ) -> Result<(), Box<dyn Error>> {
        let now = SystemTime::now()
            .duration_since(SystemTime::UNIX_EPOCH)?
            .as_secs();

        let dependencies = if config.evict_on_dependency_change == Some(true) {
            dependencies
        } else {
            vec![]
        };

        let mut builder = flexbuffers::Builder::new(&flexbuffers::BuilderOptions::SHARE_NONE);
        let mut builder_vec = builder.start_vector();

        let mut internal_vec = builder_vec.start_vector();

        internal_vec.push(now);

        let mut deps_vec = internal_vec.start_vector();

        for dep in &dependencies {
            let mut dep_vec = deps_vec.start_vector();

            match dep {
                CacheDependency::Content => {
                    dep_vec.push(0);
                }
                CacheDependency::Model(uuid) => {
                    dep_vec.push(1);
                    dep_vec.push(flexbuffers::Blob(uuid.as_ref()));
                }
            }

            dep_vec.end_vector();
        }

        deps_vec.end_vector();
        internal_vec.end_vector();

        match cache_kind {
            CacheWrite::Template(etag, last_modified, blob) => {
                builder_vec.push(etag);

                builder_vec.push(last_modified);
                builder_vec.push(flexbuffers::Blob(blob.as_ref()));
            }
            _ => unimplemented!(),
        }

        builder_vec.end_vector();

        let val = builder.view();

        let mut base_key = BytesMut::new();

        base_key.put_u8(cache_kind.as_u8());
        base_key.put_u8(idx);

        let mut key = base_key.clone();
        key.put(addr.as_bytes());

        let compression_byte = compression.map_or(0, CacheCompression::as_u8);
        let compression_str = compression.map_or("false", CacheCompression::as_str);

        key.put_u8(compression_byte);

        let size = val.len() + key.len();

        if let Some(max_size) = config.max_size
            && size > usize::try_from(max_size)?
        {
            tracing::warn!(
                address = addr,
                compressed = compression_str,
                "exceeds 'max_size' for entire cache"
            );
            return Ok(());
        }

        let mut hit_distribution = VecDeque::new();
        hit_distribution.push_back(1);

        let txn = WriteTransaction::new(self.env.clone())?;

        let mut lock = self.addresses_map.lock();

        let (total_size, total_count, addresses) = lock
            .entry((cache_kind.as_u8(), idx))
            .or_insert((0, 0, BTreeMap::new()));

        if let Some(max_size) = config.max_size
            && *total_size + size > usize::try_from(max_size)?
        {
            let mut evicted_size: usize = 0;
            let mut lock = self.eviction_queue.lock();

            let mut dep_lock = self.dependency_map.lock();

            while evicted_size < size {
                if let Some(FRsEvictionCandidate {
                    size,
                    address,
                    index,
                    ..
                }) = (*lock).pop()
                    && let Some(variations) = addresses.get_mut(&address)
                {
                    let variation = variations.remove(index);

                    for dep in variation.dependencies {
                        if let Some(dep) = dep_lock.get_mut(&dep) {
                            dep.remove(&(
                                cache_kind.as_u8(),
                                idx,
                                address.clone(),
                                u8::try_from(index)?,
                            ));
                        }
                    }

                    base_key.truncate(2);
                    base_key.put(address.as_bytes());
                    base_key.put_u8(variation.compression);

                    let mut access = txn.access();
                    if access.del_key(&self.cache_db, base_key.as_ref()).is_ok() {
                        evicted_size += size;

                        *total_count -= 1;
                        *total_size -= variation.size;
                    }
                }
            }

            drop(lock);
            drop(dep_lock);
        } else if let Some(max_count) = config.max_count
            && *total_count + 1 > max_count
        {
            let mut evicted = false;
            let mut lock = self.eviction_queue.lock();

            let mut dep_lock = self.dependency_map.lock();

            while !evicted {
                if let Some(FRsEvictionCandidate { address, index, .. }) = (*lock).pop()
                    && let Some(variations) = addresses.get_mut(&address)
                {
                    let variation = variations.remove(index);

                    for dep in variation.dependencies {
                        if let Some(dep) = dep_lock.get_mut(&dep) {
                            dep.remove(&(
                                cache_kind.as_u8(),
                                idx,
                                address.clone(),
                                u8::try_from(index)?,
                            ));
                        }
                    }

                    base_key.put(address.as_bytes());
                    base_key.put_u8(variation.compression);

                    let mut access = txn.access();
                    if access.del_key(&self.cache_db, base_key.as_ref()).is_ok() {
                        evicted = true;

                        *total_count -= 1;
                        *total_size -= variation.size;
                    }
                }
            }

            drop(lock);
            drop(dep_lock);
        }

        *total_size += size;
        *total_count += 1;

        let details = addresses.entry(addr.to_string()).or_insert(ArrayVec::new());

        let new_details = AddressDetails {
            compression: compression_byte,
            stored_at: now,
            last_hit: now,
            size,
            hit_distribution,
            dependencies: dependencies.clone(),
        };

        if let Some(existing_pos) = details
            .iter()
            .position(|v| v.compression == compression_byte)
        {
            details[existing_pos] = new_details;
        } else {
            details.push(new_details);
        }

        drop(lock);

        let mut lock = self.dependency_map.lock();

        for dependency in dependencies {
            let existing_dep = lock.entry(dependency).or_insert(BTreeSet::new());
            existing_dep.insert((cache_kind.as_u8(), idx, addr.to_string(), compression_byte));
        }

        drop(lock);

        {
            let mut access = txn.access();
            access.put(&self.cache_db, key.as_ref(), val, &put::Flags::empty())?;
        }

        txn.commit()?;

        if self.log_size {
            tracing::info!(
                size = %bytesize::ByteSize(size as u64).display().si_short(),
                compressed = compression_str,
                "stored"
            );
        } else {
            tracing::info!(compressed = compression_str, "stored");
        }

        Ok(())
    }

    #[instrument(skip(self, dependencies), err)]
    pub fn dependency_evict(
        &self,
        dependencies: Vec<CacheDependency>,
    ) -> Result<(), Box<dyn Error>> {
        let mut lock_dep_map = self.dependency_map.lock();
        let mut lock_addr_map = self.addresses_map.lock();

        let txn = WriteTransaction::new(self.env.clone())?;

        {
            let mut access = txn.access();

            for dependency in dependencies {
                if let Some(addrs) = lock_dep_map.get(&dependency) {
                    for (kind, service_idx, addr, compression_idx) in addrs {
                        if let Some((_, _, variants_map)) =
                            lock_addr_map.get_mut(&(*kind, *service_idx))
                            && let Some(variants) = variants_map.get_mut(addr)
                        {
                            variants.remove((*compression_idx) as usize);

                            let mut key = BytesMut::new();

                            key.put_u8(*kind);
                            key.put_u8(*service_idx);

                            key.put(addr.as_bytes());
                            key.put_u8(*compression_idx);

                            tracing::debug!(
                                kind,
                                i = service_idx,
                                address = addr,
                                compression = compression_idx,
                                "evicting for dependency"
                            );

                            access.del_key(&self.cache_db, key.as_ref())?;
                        }
                    }
                }

                lock_dep_map.remove(&dependency);
            }
        }

        txn.commit()?;

        drop(lock_dep_map);
        drop(lock_addr_map);

        Ok(())
    }

    #[instrument(skip(self, kind, idx), err)]
    pub fn artifact_evict(&self, kind: CacheRead, idx: u8) -> Result<(), Box<dyn Error>> {
        let mut key = BytesMut::new();

        key.put_u8(kind.as_u8());
        key.put_u8(idx);

        let mut lock_dep_map = self.dependency_map.lock();
        let mut lock_addr_map = self.addresses_map.lock();

        let txn = WriteTransaction::new(self.env.clone())?;

        {
            let mut access = txn.access();

            if let Some((total_size, total_count, addrs_map)) =
                lock_addr_map.get_mut(&(kind.as_u8(), idx))
            {
                for (addr, variants) in addrs_map.iter() {
                    key.truncate(2);

                    let addr_bytes = addr.as_bytes();
                    let base_len = addr_bytes.len() + 2;

                    key.put(addr_bytes);

                    for variant in variants {
                        key.truncate(base_len);
                        key.put_u8(variant.compression);

                        tracing::debug!(
                            kind = kind.as_u8(),
                            i = idx,
                            address = addr,
                            compression = variant.compression,
                            "evicting for artifact"
                        );

                        access.del_key(&self.cache_db, key.as_ref())?;

                        for dep in &variant.dependencies {
                            if let Some(addrs) = lock_dep_map.get_mut(dep) {
                                addrs.remove(&(
                                    kind.as_u8(),
                                    idx,
                                    addr.clone(),
                                    variant.compression,
                                ));
                            }
                        }
                    }
                }

                addrs_map.clear();

                *total_size = 0;
                *total_count = 0;

                if let Err(err) = access.del_key(&self.cache_db, &[0, kind.as_u8(), idx]) {
                    tracing::warn!(%err);
                }
            }
        }

        txn.commit()?;

        drop(lock_dep_map);
        drop(lock_addr_map);

        Ok(())
    }

    /// Cleans caches
    #[allow(clippy::missing_panics_doc, clippy::cast_precision_loss)]
    #[instrument(skip(self, cache_kind, config, idx), err)]
    pub fn clean_cache(
        &self,
        cache_kind: &CacheRead,
        config: &StoredCacheConfig,
        idx: u8,
    ) -> Result<(), Box<dyn Error>> {
        if let StoredCachePolicy::Permanent = config.policy {
            return Err("'Permanent' cache should never be cleaned up".into());
        }

        let mut key = BytesMut::new();

        key.put_u8(cache_kind.as_u8());
        key.put_u8(idx);

        let now = SystemTime::now();

        let min_stored_at = now
            .checked_sub(Duration::from_secs(config.max_ttl.unwrap_or(600))) // todo: default should come from admin
            .expect("time to work")
            .duration_since(SystemTime::UNIX_EPOCH)?
            .as_secs();

        let min_last_hit = now
            .checked_sub(Duration::from_secs(config.hit_ttl.unwrap_or(300))) // todo: default should come from admin
            .expect("time to work")
            .duration_since(SystemTime::UNIX_EPOCH)?
            .as_secs();

        let max_distribution = config.frequency_window.map(|frequency_window| {
            // todo: pass this default and a range check from admin
            let (clean_min, clean_max) = config.clean_interval.unwrap_or((60, 60 * 3));

            let avg_clean_interval = (clean_min + clean_max) as f64 / 2.0;
            frequency_window as f64 / avg_clean_interval
        });

        let mut addrs_to_remove = vec![];
        let mut eviction_queue = BinaryHeap::new();

        let mut lock = self.addresses_map.lock();

        if let Some((total_size, total_count, addresses)) = lock.get_mut(&(cache_kind.as_u8(), idx))
        {
            tracing::info!(count = total_count, size = total_size, "before");

            for (address, details) in addresses {
                for (i, variation) in details.iter_mut().enumerate() {
                    if variation.stored_at < min_stored_at || variation.last_hit < min_last_hit {
                        addrs_to_remove.push((address.clone(), variation.compression, i));
                    } else if let Some(max_distribution) = max_distribution {
                        if variation.hit_distribution.len() as f64 > max_distribution {
                            variation.hit_distribution.pop_front();
                        }

                        let total_hits: u64 = variation.hit_distribution.iter().sum();

                        match config.policy {
                            StoredCachePolicy::FRs(th_eq_threshold, lh_equality_threshold) => {
                                eviction_queue.push(FRsEvictionCandidate {
                                    total_hits: (
                                        total_hits.cast_signed(),
                                        th_eq_threshold.cast_signed(),
                                    ),
                                    last_hit: (
                                        variation.last_hit.cast_signed(),
                                        lh_equality_threshold.cast_signed(),
                                    ),
                                    size: variation.size,
                                    address: address.clone(),
                                    index: i,
                                });
                            }
                            StoredCachePolicy::Permanent => unreachable!(),
                        }
                    }
                }
            }
        }

        let txn = WriteTransaction::new(self.env.clone())?;

        let mut dep_lock = self.dependency_map.lock();

        if let Some((total_size, total_count, addresses)) = lock.get_mut(&(cache_kind.as_u8(), idx))
        {
            {
                let mut access = txn.access();

                for (remove_addr, compression, i) in &addrs_to_remove {
                    key.truncate(2);
                    key.put(remove_addr.as_bytes());
                    key.put_u8(*compression);

                    access.del_key(&self.cache_db, key.as_ref())?;

                    if let Some(variations) = addresses.get_mut(remove_addr) {
                        let variation = variations.remove(*i);

                        for dep in variation.dependencies {
                            if let Some(dep) = dep_lock.get_mut(&dep) {
                                dep.remove(&(
                                    cache_kind.as_u8(),
                                    idx,
                                    remove_addr.clone(),
                                    *compression,
                                ));
                            }
                        }

                        *total_size -= variation.size;
                        *total_count -= 1;
                    }
                }

                tracing::info!(count = total_count, size = total_size, "after");
            }
        }

        drop(dep_lock);
        drop(lock);

        txn.commit()?;

        let mut lock = self.eviction_queue.lock();
        *lock = eviction_queue;

        drop(lock);

        tracing::info!("cleaned");

        Ok(())
    }

    /// Syncs in-memory variables to disk
    #[allow(clippy::similar_names)]
    #[instrument(skip(self, cache_kind, idx), err)]
    pub fn sync(&self, cache_kind: &CacheRead, idx: u8) -> Result<(), Box<dyn Error>> {
        let mut builder = flexbuffers::Builder::new(&flexbuffers::BuilderOptions::SHARE_NONE);

        let lock = self.addresses_map.lock();

        if let Some((_total_size, _total_count, addresses)) = lock.get(&(cache_kind.as_u8(), idx)) {
            let mut addresses_vec = builder.start_vector();

            for (address, variants) in addresses {
                let mut address_vec = addresses_vec.start_vector();
                address_vec.push(address.as_str());

                let mut variants_vec = address_vec.start_vector();

                for variant in variants {
                    let mut variant_vec = variants_vec.start_vector();

                    variant_vec.push(variant.compression);
                    variant_vec.push(variant.last_hit);

                    let mut hit_distribution_vec = variant_vec.start_vector();

                    for hit_count in &variant.hit_distribution {
                        hit_distribution_vec.push(*hit_count);
                    }

                    hit_distribution_vec.end_vector();
                    variant_vec.end_vector();
                }

                variants_vec.end_vector();
                address_vec.end_vector();
            }

            addresses_vec.end_vector();
        }

        drop(lock);

        if let Ok(compressed) = zstd::stream::encode_all(std::io::Cursor::new(builder.view()), 17) {
            let txn = WriteTransaction::new(self.env.clone())?;

            {
                let mut access = txn.access();
                access.put(
                    &self.cache_db,
                    &[0, cache_kind.as_u8(), idx],
                    &compressed,
                    &put::Flags::empty(),
                )?;
            }

            txn.commit()?;

            if self.log_size {
                tracing::info!(size = %bytesize::ByteSize(compressed.len() as u64).display().si_short(), "synced");
            } else {
                tracing::info!("synced");
            }
        }

        Ok(())
    }
}