garage/src/util
Alex b44d3fc796 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: Deuxfleurs/garage#322
Co-authored-by: Alex <alex@adnab.me>
Co-committed-by: Alex <alex@adnab.me>
2022-06-08 10:01:44 +02:00
..
crdt First version of admin API (#298) 2022-05-24 12:16:39 +02:00
background.rs Make background runner terminate correctly 2022-05-17 11:38:31 +02:00
Cargo.toml Abstract database behind generic interface and implement alternative drivers (#322) 2022-06-08 10:01:44 +02:00
config.rs Abstract database behind generic interface and implement alternative drivers (#322) 2022-06-08 10:01:44 +02:00
data.rs Remove ... at end of hex IDs 2022-03-14 10:52:31 +01:00
error.rs Abstract database behind generic interface and implement alternative drivers (#322) 2022-06-08 10:01:44 +02:00
formater.rs Add a K2V client library and CLI (#303) 2022-05-18 22:24:09 +02:00
lib.rs Abstract database behind generic interface and implement alternative drivers (#322) 2022-06-08 10:01:44 +02:00
metrics.rs Add metrics to web endpoint 2022-03-14 10:53:50 +01:00
persister.rs fix clippy warnings on util and rpc 2021-05-03 22:11:41 +02:00
time.rs New buckets for 0.6.0: small fixes, including: 2022-01-04 12:46:41 +01:00
token_bucket.rs Refactoring on repair commands 2021-10-27 11:14:55 +02:00
tranquilizer.rs Add tranquilizer mechanism to improve on token bucket mechanism 2021-11-04 13:26:59 +01:00