From b44d3fc796484a50cd6854f20c9b46e5fddedc9d Mon Sep 17 00:00:00 2001 From: Alex Date: Wed, 8 Jun 2022 10:01:44 +0200 Subject: 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 Reviewed-on: https://git.deuxfleurs.fr/Deuxfleurs/garage/pulls/322 Co-authored-by: Alex Co-committed-by: Alex --- src/util/sled_counter.rs | 100 ----------------------------------------------- 1 file changed, 100 deletions(-) delete mode 100644 src/util/sled_counter.rs (limited to 'src/util/sled_counter.rs') diff --git a/src/util/sled_counter.rs b/src/util/sled_counter.rs deleted file mode 100644 index bc54cea0..00000000 --- a/src/util/sled_counter.rs +++ /dev/null @@ -1,100 +0,0 @@ -use std::sync::{ - atomic::{AtomicUsize, Ordering}, - Arc, -}; - -use sled::{CompareAndSwapError, IVec, Iter, Result, Tree}; - -#[derive(Clone)] -pub struct SledCountedTree(Arc); - -struct SledCountedTreeInternal { - tree: Tree, - len: AtomicUsize, -} - -impl SledCountedTree { - pub fn new(tree: Tree) -> Self { - let len = tree.len(); - Self(Arc::new(SledCountedTreeInternal { - tree, - len: AtomicUsize::new(len), - })) - } - - pub fn len(&self) -> usize { - self.0.len.load(Ordering::Relaxed) - } - - pub fn is_empty(&self) -> bool { - self.0.tree.is_empty() - } - - pub fn get>(&self, key: K) -> Result> { - self.0.tree.get(key) - } - - pub fn iter(&self) -> Iter { - self.0.tree.iter() - } - - // ---- writing functions ---- - - pub fn insert(&self, key: K, value: V) -> Result> - where - K: AsRef<[u8]>, - V: Into, - { - let res = self.0.tree.insert(key, value); - if res == Ok(None) { - self.0.len.fetch_add(1, Ordering::Relaxed); - } - res - } - - pub fn remove>(&self, key: K) -> Result> { - let res = self.0.tree.remove(key); - if matches!(res, Ok(Some(_))) { - self.0.len.fetch_sub(1, Ordering::Relaxed); - } - res - } - - pub fn pop_min(&self) -> Result> { - let res = self.0.tree.pop_min(); - if let Ok(Some(_)) = &res { - self.0.len.fetch_sub(1, Ordering::Relaxed); - }; - res - } - - pub fn compare_and_swap( - &self, - key: K, - old: Option, - new: Option, - ) -> Result> - where - K: AsRef<[u8]>, - OV: AsRef<[u8]>, - NV: Into, - { - let old_some = old.is_some(); - let new_some = new.is_some(); - - let res = self.0.tree.compare_and_swap(key, old, new); - - if res == Ok(Ok(())) { - match (old_some, new_some) { - (false, true) => { - self.0.len.fetch_add(1, Ordering::Relaxed); - } - (true, false) => { - self.0.len.fetch_sub(1, Ordering::Relaxed); - } - _ => (), - } - } - res - } -} -- cgit v1.2.3