Enum SyncMode

pub enum SyncMode {
    FastThenSafe,
    Safe,
    Async,
    Threshold(usize),
    Fast,
}

Disk synchronization mode.

This controls how/when the database syncs its data to disk.

Regardless of the variant chosen, dropping Env will always cause it to fully sync to disk.

Sync vs Async

All invariants except SyncMode::Async & SyncMode::Fast are synchronous, as in the database will wait until the OS has finished syncing all the data to disk before continuing.

SyncMode::Async & SyncMode::Fast are asynchronous, meaning the database will NOT wait until the data is fully synced to disk before continuing. Note that this doesn’t mean the database itself won’t be synchronized between readers/writers, but rather that the data on disk may not be immediately synchronized after a write.

Something like:

db.put("key", value);
db.get("key");

will be fine, most likely pulling from memory instead of disk.

SOMEDAY

Dynamic sync’s are not yet supported.

Only:

• SyncMode::Safe
• SyncMode::Async
• SyncMode::Fast

are supported, all other variants will panic on crate::Env::open.

Variants

FastThenSafe

Use SyncMode::Fast until fully synced, then use SyncMode::Safe.

Safe

Fully sync to disk per transaction.

Every database transaction commit will fully sync all data to disk, synchronously, so the database (writer) halts until synced.

This is expected to be very slow.

This maps to:

• LMDB without any special sync flags
• redb::Durability::Immediate

Async

Asynchrously sync to disk per transaction.

This is the same as SyncMode::Safe, but the syncs will be asynchronous, i.e. each transaction commit will sync to disk, but only eventually, not necessarily immediately.

This maps to:

• MDB_MAPASYNC
• redb::Durability::Eventual

Threshold(usize)

Fully sync to disk after we cross this transaction threshold.

After committing usize amount of database transactions, it will be sync to disk.

0 behaves the same as SyncMode::Safe, and a ridiculously large number like usize::MAX is practically the same as SyncMode::Fast.

Fast

Only flush at database shutdown.

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 disk¹.

This maps to:

• MDB_NOSYNC + MDB_MAPASYNC
• redb::Durability::Eventual

monerod reference.

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, however due to #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. ↩

Trait Implementations

impl Clone for SyncMode

fn clone(&self) -> SyncMode

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SyncMode

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for SyncMode

fn default() -> SyncMode

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for SyncMode

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Hash for SyncMode

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for SyncMode

fn cmp(&self, other: &SyncMode) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl PartialEq for SyncMode

fn eq(&self, other: &SyncMode) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl PartialOrd for SyncMode

fn partial_cmp(&self, other: &SyncMode) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for SyncMode

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for SyncMode

impl Eq for SyncMode

impl StructuralPartialEq for SyncMode

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes

Size for each variant:

• FastThenSafe: 0 bytes
• Safe: 0 bytes
• Async: 0 bytes
• Threshold: 8 bytes
• Fast: 0 bytes