mirror of
https://github.com/deuxfleurs-org/garage.git
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Abstract database behind generic interface and implement alternative drivers (#322)
- [x] Design interface - [x] Implement Sled backend - [x] Re-implement the SledCountedTree hack ~~on Sled backend~~ on all backends (i.e. over the abstraction) - [x] Convert Garage code to use generic interface - [x] Proof-read converted Garage code - [ ] Test everything well - [x] Implement sqlite backend - [x] Implement LMDB backend - [ ] (Implement Persy backend?) - [ ] (Implement other backends? (like RocksDB, ...)) - [x] Implement backend choice in config file and garage server module - [x] Add CLI for converting between DB formats - Exploit the new interface to put more things in transactions - [x] `.updated()` trigger on Garage tables Fix #284 **Bugs** - [x] When exporting sqlite, trees iterate empty?? - [x] LMDB doesn't work **Known issues for various back-ends** - Sled: - Eats all my RAM and also all my disk space - `.len()` has to traverse the whole table - Is actually quite slow on some operations - And is actually pretty bad code... - Sqlite: - Requires a lock to be taken on all operations. The lock is also taken when iterating on a table with `.iter()`, and the lock isn't released until the iterator is dropped. This means that we must be VERY carefull to not do anything else inside a `.iter()` loop or else we will have a deadlock! Most such cases have been eliminated from the Garage codebase, but there might still be some that remain. If your Garage-over-Sqlite seems to hang/freeze, this is the reason. - (adapter uses a bunch of unsafe code) - Heed (LMDB): - Not suited for 32-bit machines as it has to map the whole DB in memory. - (adpater uses a tiny bit of unsafe code) **My recommendation:** avoid 32-bit machines and use LMDB as much as possible. **Converting databases** is actually quite easy. For example from Sled to LMDB: ```bash cd src/db cargo run --features cli --bin convert -- -i path/to/garage/meta/db -a sled -o path/to/garage/meta/db.lmdb -b lmdb ``` Then, just add this to your `config.toml`: ```toml db_engine = "lmdb" ``` Co-authored-by: Alex Auvolat <alex@adnab.me> Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/322 Co-authored-by: Alex <alex@adnab.me> Co-committed-by: Alex <alex@adnab.me>
This commit is contained in:
Alex
@@ -0,0 +1,329 @@
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use core::ops::Bound;
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use core::ptr::NonNull;
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use std::collections::HashMap;
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use std::convert::TryInto;
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use std::sync::{Arc, RwLock};
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use heed::types::ByteSlice;
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use heed::{BytesDecode, Env, RoTxn, RwTxn, UntypedDatabase as Database};
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use crate::{
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Db, Error, IDb, ITx, ITxFn, Result, TxError, TxFnResult, TxOpError, TxOpResult, TxResult,
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TxValueIter, Value, ValueIter,
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};
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pub use heed;
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// -- err
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impl From<heed::Error> for Error {
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fn from(e: heed::Error) -> Error {
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Error(format!("LMDB: {}", e).into())
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}
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}
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impl From<heed::Error> for TxOpError {
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fn from(e: heed::Error) -> TxOpError {
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TxOpError(e.into())
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}
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}
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// -- db
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pub struct LmdbDb {
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db: heed::Env,
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trees: RwLock<(Vec<Database>, HashMap<String, usize>)>,
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}
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impl LmdbDb {
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pub fn init(db: Env) -> Db {
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let s = Self {
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db,
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trees: RwLock::new((Vec::new(), HashMap::new())),
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};
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Db(Arc::new(s))
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}
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fn get_tree(&self, i: usize) -> Result<Database> {
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self.trees
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.read()
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.unwrap()
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.0
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.get(i)
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.cloned()
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.ok_or_else(|| Error("invalid tree id".into()))
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}
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}
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impl IDb for LmdbDb {
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fn engine(&self) -> String {
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"LMDB (using Heed crate)".into()
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}
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fn open_tree(&self, name: &str) -> Result<usize> {
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let mut trees = self.trees.write().unwrap();
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if let Some(i) = trees.1.get(name) {
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Ok(*i)
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} else {
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let tree = self.db.create_database(Some(name))?;
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let i = trees.0.len();
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trees.0.push(tree);
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trees.1.insert(name.to_string(), i);
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Ok(i)
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}
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}
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fn list_trees(&self) -> Result<Vec<String>> {
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let tree0 = match self.db.open_database::<heed::types::Str, ByteSlice>(None)? {
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Some(x) => x,
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None => return Ok(vec![]),
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};
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let mut ret = vec![];
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let tx = self.db.read_txn()?;
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for item in tree0.iter(&tx)? {
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let (tree_name, _) = item?;
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ret.push(tree_name.to_string());
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}
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drop(tx);
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let mut ret2 = vec![];
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for tree_name in ret {
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if self
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.db
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.open_database::<ByteSlice, ByteSlice>(Some(&tree_name))?
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.is_some()
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{
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ret2.push(tree_name);
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}
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}
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Ok(ret2)
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}
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// ----
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fn get(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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let val = tree.get(&tx, key)?;
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match val {
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None => Ok(None),
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Some(v) => Ok(Some(v.to_vec())),
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}
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}
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fn len(&self, tree: usize) -> Result<usize> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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Ok(tree.len(&tx)?.try_into().unwrap())
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}
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fn insert(&self, tree: usize, key: &[u8], value: &[u8]) -> Result<Option<Value>> {
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let tree = self.get_tree(tree)?;
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let mut tx = self.db.write_txn()?;
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let old_val = tree.get(&tx, key)?.map(Vec::from);
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tree.put(&mut tx, key, value)?;
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tx.commit()?;
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Ok(old_val)
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}
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fn remove(&self, tree: usize, key: &[u8]) -> Result<Option<Value>> {
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let tree = self.get_tree(tree)?;
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let mut tx = self.db.write_txn()?;
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let old_val = tree.get(&tx, key)?.map(Vec::from);
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tree.delete(&mut tx, key)?;
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tx.commit()?;
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Ok(old_val)
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}
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fn iter(&self, tree: usize) -> Result<ValueIter<'_>> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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TxAndIterator::make(tx, |tx| Ok(tree.iter(tx)?))
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}
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fn iter_rev(&self, tree: usize) -> Result<ValueIter<'_>> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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TxAndIterator::make(tx, |tx| Ok(tree.rev_iter(tx)?))
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}
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fn range<'r>(
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&self,
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tree: usize,
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low: Bound<&'r [u8]>,
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high: Bound<&'r [u8]>,
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) -> Result<ValueIter<'_>> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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TxAndIterator::make(tx, |tx| Ok(tree.range(tx, &(low, high))?))
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}
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fn range_rev<'r>(
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&self,
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tree: usize,
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low: Bound<&'r [u8]>,
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high: Bound<&'r [u8]>,
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) -> Result<ValueIter<'_>> {
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let tree = self.get_tree(tree)?;
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let tx = self.db.read_txn()?;
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TxAndIterator::make(tx, |tx| Ok(tree.rev_range(tx, &(low, high))?))
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}
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// ----
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fn transaction(&self, f: &dyn ITxFn) -> TxResult<(), ()> {
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let trees = self.trees.read().unwrap();
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let mut tx = LmdbTx {
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trees: &trees.0[..],
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tx: self
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.db
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.write_txn()
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.map_err(Error::from)
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.map_err(TxError::Db)?,
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};
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let res = f.try_on(&mut tx);
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match res {
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TxFnResult::Ok => {
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tx.tx.commit().map_err(Error::from).map_err(TxError::Db)?;
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Ok(())
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}
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TxFnResult::Abort => {
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tx.tx.abort().map_err(Error::from).map_err(TxError::Db)?;
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Err(TxError::Abort(()))
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}
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TxFnResult::DbErr => {
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tx.tx.abort().map_err(Error::from).map_err(TxError::Db)?;
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Err(TxError::Db(Error(
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"(this message will be discarded)".into(),
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)))
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}
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}
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}
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}
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// ----
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struct LmdbTx<'a> {
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trees: &'a [Database],
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tx: RwTxn<'a, 'a>,
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}
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impl<'a> LmdbTx<'a> {
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fn get_tree(&self, i: usize) -> TxOpResult<&Database> {
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self.trees.get(i).ok_or_else(|| {
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TxOpError(Error(
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"invalid tree id (it might have been openned after the transaction started)".into(),
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))
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})
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}
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}
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impl<'a> ITx for LmdbTx<'a> {
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fn get(&self, tree: usize, key: &[u8]) -> TxOpResult<Option<Value>> {
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let tree = self.get_tree(tree)?;
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match tree.get(&self.tx, key)? {
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Some(v) => Ok(Some(v.to_vec())),
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None => Ok(None),
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}
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}
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fn len(&self, _tree: usize) -> TxOpResult<usize> {
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unimplemented!(".len() in transaction not supported with LMDB backend")
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}
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fn insert(&mut self, tree: usize, key: &[u8], value: &[u8]) -> TxOpResult<Option<Value>> {
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let tree = *self.get_tree(tree)?;
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let old_val = tree.get(&self.tx, key)?.map(Vec::from);
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tree.put(&mut self.tx, key, value)?;
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Ok(old_val)
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}
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fn remove(&mut self, tree: usize, key: &[u8]) -> TxOpResult<Option<Value>> {
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let tree = *self.get_tree(tree)?;
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let old_val = tree.get(&self.tx, key)?.map(Vec::from);
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tree.delete(&mut self.tx, key)?;
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Ok(old_val)
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}
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fn iter(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
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unimplemented!("Iterators in transactions not supported with LMDB backend");
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}
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fn iter_rev(&self, _tree: usize) -> TxOpResult<TxValueIter<'_>> {
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unimplemented!("Iterators in transactions not supported with LMDB backend");
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}
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fn range<'r>(
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&self,
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_tree: usize,
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_low: Bound<&'r [u8]>,
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_high: Bound<&'r [u8]>,
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) -> TxOpResult<TxValueIter<'_>> {
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unimplemented!("Iterators in transactions not supported with LMDB backend");
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}
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fn range_rev<'r>(
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&self,
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_tree: usize,
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_low: Bound<&'r [u8]>,
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_high: Bound<&'r [u8]>,
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) -> TxOpResult<TxValueIter<'_>> {
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unimplemented!("Iterators in transactions not supported with LMDB backend");
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}
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}
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// ----
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type IteratorItem<'a> = heed::Result<(
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<ByteSlice as BytesDecode<'a>>::DItem,
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<ByteSlice as BytesDecode<'a>>::DItem,
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)>;
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struct TxAndIterator<'a, I>
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where
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I: Iterator<Item = IteratorItem<'a>> + 'a,
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{
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tx: RoTxn<'a>,
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iter: Option<I>,
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}
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impl<'a, I> TxAndIterator<'a, I>
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where
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I: Iterator<Item = IteratorItem<'a>> + 'a,
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{
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fn make<F>(tx: RoTxn<'a>, iterfun: F) -> Result<ValueIter<'a>>
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where
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F: FnOnce(&'a RoTxn<'a>) -> Result<I>,
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{
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let mut res = TxAndIterator { tx, iter: None };
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let tx = unsafe { NonNull::from(&res.tx).as_ref() };
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res.iter = Some(iterfun(tx)?);
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Ok(Box::new(res))
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}
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}
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impl<'a, I> Drop for TxAndIterator<'a, I>
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where
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I: Iterator<Item = IteratorItem<'a>> + 'a,
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{
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fn drop(&mut self) {
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drop(self.iter.take());
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}
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}
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impl<'a, I> Iterator for TxAndIterator<'a, I>
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where
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I: Iterator<Item = IteratorItem<'a>> + 'a,
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{
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type Item = Result<(Value, Value)>;
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fn next(&mut self) -> Option<Self::Item> {
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match self.iter.as_mut().unwrap().next() {
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None => None,
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Some(Err(e)) => Some(Err(e.into())),
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Some(Ok((k, v))) => Some(Ok((k.to_vec(), v.to_vec()))),
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}
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}
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}
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