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database: workaround redb page freeing issue (#225)

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* redb: `SyncMode::Fast` => `redb::Durability::Eventual`

* redb: fix clippy

* database: document `SyncMode`
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hinto-janai 2024-07-10 17:11:09 -04:00 committed by GitHub
parent 303c165df7
commit 612938eae6
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2 changed files with 17 additions and 8 deletions
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5
storage/database/src/backend/redb/env.rs
View file

@ -56,8 +56,9 @@ impl Env for ConcreteEnv {
// <https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.Paranoid>
// should we use that instead of Immediate?
SyncMode::Safe => redb::Durability::Immediate,
SyncMode::Async => redb::Durability::Eventual,
SyncMode::Fast => redb::Durability::None,
// FIXME: `Fast` maps to `Eventual` instead of `None` because of:
// <https://github.com/Cuprate/cuprate/issues/149>
SyncMode::Async | SyncMode::Fast => redb::Durability::Eventual,
// SOMEDAY: dynamic syncs are not implemented.
SyncMode::FastThenSafe | SyncMode::Threshold(_) => unimplemented!(),
};

20
storage/database/src/config/sync_mode.rs
View file

@ -84,7 +84,7 @@ pub enum SyncMode {
///
/// This is expected to be very slow.
///
/// This matches:
/// This maps to:
/// - LMDB without any special sync flags
/// - [`redb::Durability::Immediate`](https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.Immediate)
Safe,
@ -96,7 +96,7 @@ pub enum SyncMode {
/// each transaction commit will sync to disk,
/// but only eventually, not necessarily immediately.
///
/// This matches:
/// This maps to:
/// - [`MDB_MAPASYNC`](http://www.lmdb.tech/doc/group__mdb__env.html#gab034ed0d8e5938090aef5ee0997f7e94)
/// - [`redb::Durability::Eventual`](https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.Eventual)
Async,
@ -115,17 +115,25 @@ pub enum SyncMode {
/// This is the fastest, yet unsafest option.
///
/// It will cause the database to never _actively_ sync,
/// letting the OS decide when to flush data to disk.
/// letting the OS decide when to flush data to disk[^1].
///
/// This matches:
/// This maps to:
/// - [`MDB_NOSYNC`](http://www.lmdb.tech/doc/group__mdb__env.html#ga5791dd1adb09123f82dd1f331209e12e) + [`MDB_MAPASYNC`](http://www.lmdb.tech/doc/group__mdb__env.html#gab034ed0d8e5938090aef5ee0997f7e94)
/// - [`redb::Durability::None`](https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.None)
/// - [`redb::Durability::Eventual`](https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.Eventual)
///
/// `monerod` reference: <https://github.com/monero-project/monero/blob/7b7958bbd9d76375c47dc418b4adabba0f0b1785/src/blockchain_db/lmdb/db_lmdb.cpp#L1380-L1381>
/// [`monerod` reference](https://github.com/monero-project/monero/blob/7b7958bbd9d76375c47dc418b4adabba0f0b1785/src/blockchain_db/lmdb/db_lmdb.cpp#L1380-L1381).
///
/// # Corruption
/// In the case of a system crash, the database
/// may become corrupted when using this option.
///
/// [^1]:
/// Semantically, this variant would actually map to
/// [`redb::Durability::None`](https://docs.rs/redb/1.5.0/redb/enum.Durability.html#variant.None),
/// however due to [`#149`](https://github.com/Cuprate/cuprate/issues/149),
/// this is not possible. As such, when using the `redb` backend,
/// transaction writes "should be persistent some time after `WriteTransaction::commit` returns."
/// Thus, [`SyncMode::Async`] will map to the same `redb::Durability::Eventual` as [`SyncMode::Fast`].
//
// FIXME: we could call this `unsafe`
// and use that terminology in the config file