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//! An ergonomic, multithreaded API for an LMDB datastore use crate::{ key_val_store::{error::KeyValStoreError, key_val_store::IterationResult}, lmdb_store::error::LMDBError, }; use lmdb_zero::{ db, error::{self, LmdbResultExt}, open, put, traits::AsLmdbBytes, ConstAccessor, Cursor, CursorIter, Database, DatabaseOptions, EnvBuilder, Environment, Ignore, MaybeOwned, ReadTransaction, Stat, WriteAccessor, WriteTransaction, }; use log::*; use serde::{de::DeserializeOwned, Serialize}; use std::{ cmp::max, collections::HashMap, path::{Path, PathBuf}, sync::Arc, }; const LOG_TARGET: &str = "lmdb"; /// An atomic pointer to an LMDB database instance type DatabaseRef = Arc<Database<'static>>; /// A builder for [LMDBStore](struct.lmdbstore.html) /// ## Example /// /// Create a new LMDB database of 500MB in the `db` directory with two named databases: "db1" and "db2" /// /// ``` /// # use tari_storage::lmdb_store::LMDBBuilder; /// # use lmdb_zero::db; /// # use std::env; /// let mut store = LMDBBuilder::new() /// .set_path(env::temp_dir()) /// .set_environment_size(500) /// .set_max_number_of_databases(10) /// .add_database("db1", db::CREATE) /// .add_database("db2", db::CREATE) /// .build() /// .unwrap(); /// ``` #[derive(Default)] pub struct LMDBBuilder { path: PathBuf, db_size_mb: usize, max_dbs: usize, db_names: HashMap<String, db::Flags>, } impl LMDBBuilder { /// Create a new LMDBStore builder. Set up the database by calling `set_nnnn` and then create the database /// with `build()`. The default values for the database parameters are: /// /// | Parameter | Default | /// |:----------|---------| /// | path | ./store/| /// | size | 64 MB | /// | named DBs | none | pub fn new() -> LMDBBuilder { LMDBBuilder { path: "./store/".into(), db_size_mb: 64, db_names: HashMap::new(), max_dbs: 8, } } /// Set the directory where the LMDB database exists, or must be created. /// Note: The directory must exist already; it is not created for you. If it does not exist, `build()` will /// return `LMDBError::InvalidPath`. pub fn set_path<P: AsRef<Path>>(mut self, path: P) -> LMDBBuilder { self.path = path.as_ref().to_owned(); self } /// Sets the size of the environment, in MB. /// The actual memory will only be allocated when #build() is called pub fn set_environment_size(mut self, size: usize) -> LMDBBuilder { self.db_size_mb = size; self } /// Sets the maximum number of databases (tables) in the environment. If this value is less than the number of /// DBs that will be created when the environment is built, this value will be ignored. pub fn set_max_number_of_databases(mut self, size: usize) -> LMDBBuilder { self.max_dbs = size; self } /// Add an additional named database to the LMDB environment.If `add_database` isn't called at least once, only the /// `default` database is created. pub fn add_database(mut self, name: &str, flags: db::Flags) -> LMDBBuilder { // There will always be a 'default' database let _ = self.db_names.insert(name.into(), flags); self } /// Create a new LMDBStore instance and open the underlying database environment pub fn build(mut self) -> Result<LMDBStore, LMDBError> { let max_dbs = max(self.db_names.len(), self.max_dbs) as u32; if !self.path.exists() { return Err(LMDBError::InvalidPath); } let path = self .path .to_str() .map(String::from) .ok_or_else(|| LMDBError::InvalidPath)?; let env = unsafe { let mut builder = EnvBuilder::new()?; builder.set_mapsize(self.db_size_mb * 1024 * 1024)?; builder.set_maxdbs(max_dbs)?; // Using open::Flags::NOTLS does not compile!?! NOTLS=0x200000 let flags = open::Flags::from_bits(0x200_000).expect("LMDB open::Flag is correct"); builder.open(&path, flags, 0o600)? }; let env = Arc::new(env); // Increase map size if usage gets close to the db size let mut env_info = env.info()?; let env_stat = env.stat()?; let size_used = env_stat.psize as usize * env_info.last_pgno; let mut space_remaining = env_info.mapsize - size_used; let usage = (size_used as f64 / env_info.mapsize as f64) * 100.0; if space_remaining <= ((self.db_size_mb * 1024 * 1024) as f64 * 0.5) as usize { unsafe { env.set_mapsize(size_used + self.db_size_mb * 1024 * 1024)?; } env_info = env.info()?; space_remaining = env_info.mapsize - size_used; debug!( target: LOG_TARGET, "({}) LMDB environment usage factor {:.*} %., size used {:?} MB, increased by {:?} MB.", path, 2, usage, size_used / (1024 * 1024), self.db_size_mb ); }; info!( target: LOG_TARGET, "({}) LMDB environment created with a capacity of {} MB, {} MB remaining.", path, env_info.mapsize / (1024 * 1024), space_remaining / (1024 * 1024) ); let mut databases: HashMap<String, LMDBDatabase> = HashMap::new(); if self.db_names.is_empty() { self = self.add_database("default", db::CREATE); } for (name, flags) in self.db_names.iter() { let db = Database::open(env.clone(), Some(name), &DatabaseOptions::new(*flags))?; let db = LMDBDatabase { name: name.to_string(), env: env.clone(), db: Arc::new(db), }; databases.insert(name.to_string(), db); trace!(target: LOG_TARGET, "({}) LMDB database '{}' is ready", path, name); } Ok(LMDBStore { path, env, databases }) } } /// A Struct for holding state for an LM Database. LMDB is memory mapped, so you can treat the DB as an (essentially) /// infinitely large memory-backed hashmap. A single environment is stored in one file. The individual databases /// are key-value tables stored within the file. /// /// LMDB databases are thread-safe. /// /// To create an instance of LMDBStore, use [LMDBBuilder](struct.lmdbbuilder.html). /// /// ## Memory efficiency /// /// LMDB really only understands raw byte arrays. Complex structures need to be referenced as (what looks like) a /// single contiguous blob of memory. This presents some trade offs we need to make when `insert`ing and `get`ting /// data to/from LMDB. /// /// ### Writing /// /// For simple types, like `PublickKey([u8; 32])`, it's most efficient to pass a pointer to the memory position; and /// LMDB will do (at most) a single copy into its memory structures. the lmdb-zero crate assumes this by only /// requiring the `AsLmdbBytes` trait when `insert`ing data. i.e. `insert` does does take ownership of the key or /// value; it just wants to be able to read the `[u8]`. /// /// This poses something of a problem for complex structures. Structs typically don't have a contiguous block of /// memory backing the instance, and so you either need to impose one (which isn't a great idea-- now you have to write /// some sort of memory management software), or you eat the cost of doing an intermediate copy into a buffer every /// time you need to commit a structure to LMDB. /// /// However, this cost is mitigated if there's any kind of processing that needs to be done in converting `T` to /// `[u8]` (e.g. if an IP address is stored as a string for some reason, you might want to represent it as `[u8; 4]`) /// , which probably happens more often than we think, and offers maximum flexibility. /// /// Furthermore, the "simple" types are typically quite small, so an additional copy is not usually incurring much /// overhead. /// /// So this library makes the trade-off of carrying out two copies per write whilst gaining a significant amount of /// flexibility in the process. /// /// ### Reading /// /// When LMDB returns data from a `get` request, it returns a `&[u8]` - you cannot take ownership of this data. /// Therefore we necessarily need to copy data anyway in order to pull data into the final Struct instance. /// So the `From<&[u8]> for T` trait implementation will work for reading, and this works fine for both simple and /// complex data structures. /// /// `FromLmdbBytes` is not quite what we want because the trait function returns a reference to an object, rather /// than the object itself. /// /// An additional consideration is: how was this data serialised? If the writing was a straight memory dump, we /// don't always have enough information to reconstruct our data object (how long was a string? How many elements /// were in the array? Was it big- or little-endian ordering of integers?). /// /// If we have to store this metadata when reading in byte strings, it means it had to be stored too. This is a /// further roadblock to the "zero-copy" ideal for writing. And since we're now basically serialising and /// de-serialising, we may as well use a well-known, highly efficient binary format to do so. /// /// ## Serialisation /// /// The ideal serialiasation format is the one that does the least "bit-twiddling" between memory and the byte array; /// as well as being as compact as possible. /// /// Candidates include: Bincode, MsgPack, and Protobuf / Cap'nProto. Without spending ages on a comparison, I just /// took the benchmark results from [this project](https://github.com/erickt/rust-serialization-benchmarks): /// /// ```text /// test clone ... bench: 1,179 ns/iter (+/- 115) = 444 MB/s /// /// test capnp_deserialize ... bench: 277 ns/iter (+/- 27) = 1617 MB/s ** /// test flatbuffers_deserialize ... bench: 0 ns/iter (+/- 0) = 472000 MB/s *** /// test rust_bincode_deserialize ... bench: 1,533 ns/iter (+/- 228) = 260 MB/s /// test rmp_serde_deserialize ... bench: 1,859 ns/iter (+/- 186) = 154 MB/s /// test rust_protobuf_deserialize ... bench: 558 ns/iter (+/- 29) = 512 MB/s * /// test serde_json_deserialize ... bench: 2,244 ns/iter (+/- 249) = 269 MB/s /// /// test capnp_serialize ... bench: 28 ns/iter (+/- 5) = 16000 MB/s ** /// test flatbuffers_serialize ... bench: 0 ns/iter (+/- 0) = 472000 MB/s *** /// test rmp_serde_serialize ... bench: 278 ns/iter (+/- 27) = 1032 MB/s /// test rust_bincode_serialize ... bench: 190 ns/iter (+/- 43) = 2105 MB/s * /// test rust_protobuf_serialize ... bench: 468 ns/iter (+/- 18) = 611 MB/s /// test serde_json_serialize ... bench: 1,012 ns/iter (+/- 55) = 597 MB/s /// ``` /// /// Based on these benchmarks, Flatbuffers and Cap'nProto are far and away the quickest. However, looking at the /// benchmarks more closely, we see that these aren't strictly Orange to Orange comparisons. The flatbuffers and /// capnproto tests don't actually serialise to and from the general Rust struct (an HTTP request type template), but /// from specially generated structs based on the schema. /// /// Strictly speaking, if we're going to serialise arbitrary key-value types, these benchmarks should include the /// time it takes to populate a flatbuffer / capnproto structure. /// /// A quick modification of the benchmarks to take this int account this reveals: /// /// ```text /// test rust_bincode_deserialize ... bench: 1,505 ns/iter (+/- 361) = 265 MB/s * /// test capnp_deserialize ... bench: 282 ns/iter (+/- 37) = 1588 MB/s *** /// test rmp_serde_deserialize ... bench: 1,800 ns/iter (+/- 144) = 159 MB/s * /// /// test capnp_serialize ... bench: 941 ns/iter (+/- 40) = 476 MB/s * /// test rmp_serde_serialize ... bench: 269 ns/iter (+/- 19) = 1066 MB/s ** /// test rust_bincode_serialize ... bench: 191 ns/iter (+/- 41) = 1114 MB/s *** /// ``` /// /// Now bincode emerges as a reasonable contender. Another positive to bincode is that one doesn't have to update and /// maintain a schema for the data types begin serialized, nor is a separate compilation step required. /// /// So after all this, we'll use bincode for the time being to handle serialisation to- and from- LMDB pub struct LMDBStore { path: String, pub(crate) env: Arc<Environment>, pub(crate) databases: HashMap<String, LMDBDatabase>, } /// Close all databases and close the environment. You cannot be guaranteed that the dbs will be closed after calling /// this function because there still may be threads accessing / writing to a database that will block this call. /// However, in that case `shutdown` returns an error. impl LMDBStore { pub fn flush(&self) -> Result<(), lmdb_zero::error::Error> { trace!(target: LOG_TARGET, "Forcing flush of buffers to disk"); self.env.sync(true)?; debug!(target: LOG_TARGET, "LMDB Buffers have been flushed"); Ok(()) } pub fn log_info(&self) { match self.env.info() { Err(e) => warn!( target: LOG_TARGET, "Could not retrieve LMDB information for {}. {}", self.path, e.to_string() ), Ok(info) => { let size_mb = info.mapsize / 1024 / 1024; debug!( target: LOG_TARGET, "LMDB Environment information ({}). Map Size={} MB. Last page no={}. Last tx id={}", self.path, size_mb, info.last_pgno, info.last_txnid ) }, } match self.env.stat() { Err(e) => warn!( target: LOG_TARGET, "Could not retrieve LMDB statistics for {}. {}", self.path, e.to_string() ), Ok(stats) => { let page_size = stats.psize / 1024; debug!( target: LOG_TARGET, "LMDB Environment statistics ({}). Page size={}kB. Tree depth={}. Branch pages={}. Leaf Pages={}, \ Overflow pages={}, Entries={}", self.path, page_size, stats.depth, stats.branch_pages, stats.leaf_pages, stats.overflow_pages, stats.entries ); }, } } /// Returns a handle to the database given in `db_name`, if it exists, otherwise return None. pub fn get_handle(&self, db_name: &str) -> Option<LMDBDatabase> { match self.databases.get(db_name) { Some(db) => Some(db.clone()), None => None, } } pub fn env(&self) -> Arc<Environment> { self.env.clone() } } #[derive(Clone)] pub struct LMDBDatabase { name: String, env: Arc<Environment>, db: DatabaseRef, } impl LMDBDatabase { /// Inserts a record into the database. This is an atomic operation. Internally, `insert` creates a new /// write transaction, writes the value, and then commits the transaction. pub fn insert<K, V>(&self, key: &K, value: &V) -> Result<(), LMDBError> where K: AsLmdbBytes + ?Sized, V: Serialize, { let env = &(*self.db.env()); let tx = WriteTransaction::new(env)?; { let mut accessor = tx.access(); let buf = LMDBWriteTransaction::convert_value(value)?; accessor.put(&*self.db, key, &buf, put::Flags::empty())?; } tx.commit().map_err(LMDBError::from) } /// Get a value from the database. This is an atomic operation. A read transaction is created, the value /// extracted, copied and converted to V before closing the transaction. A copy is unavoidable because the /// extracted byte string is released when the transaction is closed. If you are doing many `gets`, it is more /// efficient to use `with_read_transaction` pub fn get<K, V>(&self, key: &K) -> Result<Option<V>, LMDBError> where K: AsLmdbBytes + ?Sized, for<'t> V: DeserializeOwned, // read this as, for *any* lifetime, t, we can convert a [u8] to V { let env = &(*self.db.env()); let txn = ReadTransaction::new(env)?; let accessor = txn.access(); let val = accessor.get(&self.db, key).to_opt(); LMDBReadTransaction::convert_value(val) } /// Return statistics about the database, See [Stat](lmdb_zero/struct.Stat.html) for more details. pub fn get_stats(&self) -> Result<Stat, LMDBError> { let env = &(*self.db.env()); Ok(ReadTransaction::new(env).and_then(|txn| txn.db_stat(&self.db))?) } /// Log some pretty printed stats.See [Stat](lmdb_zero/struct.Stat.html) for more details. pub fn log_info(&self) { match self.get_stats() { Err(e) => warn!( target: LOG_TARGET, "Could not retrieve LMDB statistics for {}. {}", self.name, e.to_string() ), Ok(stats) => { let page_size = stats.psize / 1024; debug!( target: LOG_TARGET, "LMDB Database statistics ({}). Page size={}kB. Tree depth={}. Branch pages={}. Leaf Pages={}, \ Overflow pages={}, Entries={}", self.name, page_size, stats.depth, stats.branch_pages, stats.leaf_pages, stats.overflow_pages, stats.entries ); }, } } /// Returns if the database is empty. pub fn is_empty(&self) -> Result<bool, LMDBError> { self.get_stats().and_then(|s| Ok(s.entries > 0)) } /// Returns the total number of entries in this database. pub fn len(&self) -> Result<usize, LMDBError> { self.get_stats().and_then(|s| Ok(s.entries)) } /// Execute function `f` for each value in the database. /// /// The underlying LMDB library does not permit database cursors to be returned from functions to preserve Rust /// memory guarantees, so this is the closest thing to an iterator that you're going to get :/ /// /// `f` is a closure of form `|pair: Result<(K,V), LMDBError>| -> IterationResult`. If `IterationResult::Break` is /// returned the closure will not be called again and `for_each` will return. You will usually need to include /// type inference to let Rust know which type to deserialise to: /// ```nocompile /// let res = db.for_each::<Key, User, _>(|pair| { /// let (key, user) = pair.unwrap(); /// //.. do stuff with key and user.. /// }); pub fn for_each<K, V, F>(&self, mut f: F) -> Result<(), LMDBError> where K: DeserializeOwned, V: DeserializeOwned, F: FnMut(Result<(K, V), KeyValStoreError>) -> IterationResult, { let env = self.env.clone(); let db = self.db.clone(); let txn = ReadTransaction::new(env)?; let access = txn.access(); let cursor = txn.cursor(db)?; let head = |c: &mut Cursor, a: &ConstAccessor| { let (key_bytes, val_bytes) = c.first(a)?; ReadOnlyIterator::deserialize::<K, V>(key_bytes, val_bytes) }; let cursor = MaybeOwned::Owned(cursor); let iter = CursorIter::new(cursor, &access, head, ReadOnlyIterator::next)?; for p in iter { match f(p.map_err(|e| KeyValStoreError::DatabaseError(e.to_string()))) { IterationResult::Break => break, IterationResult::Continue => {}, } } Ok(()) } /// Checks whether a key exists in this database pub fn contains_key<K>(&self, key: &K) -> Result<bool, LMDBError> where K: AsLmdbBytes + ?Sized { let txn = ReadTransaction::new(&(*self.db.env()))?; let accessor = txn.access(); let res: error::Result<&Ignore> = accessor.get(&self.db, key); let res = res.to_opt()?.is_some(); Ok(res) } /// Delete a record associated with `key` from the database. If the key is not found, pub fn remove<K>(&self, key: &K) -> Result<(), LMDBError> where K: AsLmdbBytes + ?Sized { let tx = WriteTransaction::new(&(*self.db.env()))?; { let mut accessor = tx.access(); accessor.del_key(&self.db, key)?; } tx.commit().map_err(Into::into) } /// Create a read-only transaction on the current database and execute the instructions given in the closure. The /// transaction is automatically committed when the closure goes out of scope. You may provide the results of the /// transaction to the calling scope by populating a `Vec<V>` with the results of `txn.get(k)`. Otherwise, if the /// results are not needed, or you did not call `get`, just return `Ok(None)`. pub fn with_read_transaction<F, V>(&self, f: F) -> Result<Option<Vec<V>>, LMDBError> where V: serde::de::DeserializeOwned, F: FnOnce(LMDBReadTransaction) -> Result<Option<Vec<V>>, LMDBError>, { let txn = ReadTransaction::new(self.env.clone())?; let access = txn.access(); let wrapper = LMDBReadTransaction { db: &self.db, access }; f(wrapper) } /// Create a transaction with write access on the current table. pub fn with_write_transaction<F>(&self, f: F) -> Result<(), LMDBError> where F: FnOnce(LMDBWriteTransaction) -> Result<(), LMDBError> { let txn = WriteTransaction::new(self.env.clone())?; let access = txn.access(); let wrapper = LMDBWriteTransaction { db: &self.db, access }; f(wrapper)?; txn.commit().map_err(|e| LMDBError::CommitError(e.to_string())) } /// Returns an owned atomic reference to the database pub fn db(&self) -> DatabaseRef { self.db.clone() } } /// Helper functions for the `for_each` method struct ReadOnlyIterator {} impl ReadOnlyIterator { fn deserialize<K, V>(key_bytes: &[u8], val_bytes: &[u8]) -> Result<(K, V), error::Error> where for<'t> K: serde::de::DeserializeOwned, for<'t> V: serde::de::DeserializeOwned, { let key = bincode::deserialize(key_bytes).map_err(|e| error::Error::ValRejected(e.to_string()))?; let val = bincode::deserialize(val_bytes).map_err(|e| error::Error::ValRejected(e.to_string()))?; Ok((key, val)) } fn next<'r, K, V>(c: &mut Cursor, access: &'r ConstAccessor) -> Result<(K, V), error::Error> where K: serde::de::DeserializeOwned, V: serde::de::DeserializeOwned, { let (key_bytes, val_bytes) = c.next(access)?; ReadOnlyIterator::deserialize(key_bytes, val_bytes) } } pub struct LMDBReadTransaction<'txn, 'db: 'txn> { db: &'db Database<'db>, access: ConstAccessor<'txn>, } impl<'txn, 'db: 'txn> LMDBReadTransaction<'txn, 'db> { /// Get and deserialise a value from the database. pub fn get<K, V>(&self, key: &K) -> Result<Option<V>, LMDBError> where K: AsLmdbBytes + ?Sized, for<'t> V: serde::de::DeserializeOwned, // read this as, for *any* lifetime, t, we can convert a [u8] to V { let val = self.access.get(&self.db, key).to_opt(); LMDBReadTransaction::convert_value(val) } /// Checks whether a key exists in this database pub fn exists<K>(&self, key: &K) -> Result<bool, LMDBError> where K: AsLmdbBytes + ?Sized { let res: error::Result<&Ignore> = self.access.get(&self.db, key); let res = res.to_opt()?.is_some(); Ok(res) } fn convert_value<V>(val: Result<Option<&[u8]>, error::Error>) -> Result<Option<V>, LMDBError> where for<'t> V: serde::de::DeserializeOwned /* read this as, for *any* lifetime, t, we can convert a [u8] to V */ { match val { Ok(None) => Ok(None), Err(e) => Err(LMDBError::GetError(format!("LMDB get error: {}", e.to_string()))), Ok(Some(v)) => match bincode::deserialize(v) { // The reference to v is about to be dropped, so we must copy the data now Ok(val) => Ok(Some(val)), Err(e) => Err(LMDBError::GetError(format!("LMDB get error: {}", e))), }, } } } pub struct LMDBWriteTransaction<'txn, 'db: 'txn> { db: &'db Database<'db>, access: WriteAccessor<'txn>, } impl<'txn, 'db: 'txn> LMDBWriteTransaction<'txn, 'db> { pub fn insert<K, V>(&mut self, key: &K, value: &V) -> Result<(), LMDBError> where K: AsLmdbBytes + ?Sized, V: serde::Serialize, { let buf = Self::convert_value(value)?; self.access.put(&self.db, key, &buf, put::Flags::empty())?; Ok(()) } /// Checks whether a key exists in this database pub fn exists<K>(&self, key: &K) -> Result<bool, LMDBError> where K: AsLmdbBytes + ?Sized { let res: error::Result<&Ignore> = self.access.get(&self.db, key); let res = res.to_opt()?.is_some(); Ok(res) } pub fn delete<K>(&mut self, key: &K) -> Result<(), LMDBError> where K: AsLmdbBytes + ?Sized { Ok(self.access.del_key(&self.db, key)?) } fn convert_value<V>(value: &V) -> Result<Vec<u8>, LMDBError> where V: serde::Serialize { let size = bincode::serialized_size(value).map_err(|e| LMDBError::SerializationErr(e.to_string()))?; let mut buf = Vec::with_capacity(size as usize); bincode::serialize_into(&mut buf, value).map_err(|e| LMDBError::SerializationErr(e.to_string()))?; Ok(buf) } } #[cfg(test)] mod test { use crate::lmdb_store::LMDBBuilder; use lmdb_zero::db; use std::env; #[test] fn test_lmdb_builder() { let store = LMDBBuilder::new() .set_path(env::temp_dir()) .set_environment_size(500) .set_max_number_of_databases(10) .add_database("db1", db::CREATE) .add_database("db2", db::CREATE) .build() .unwrap(); assert!(&store.databases.len() == &2); } }