Struct garage_table::crdt::LwwMap [−][src]
pub struct LwwMap<K, V> { /* fields omitted */ }
Expand description
Last Write Win Map
This types defines a CRDT for a map from keys to values.
The values have an associated timestamp, such that the last written value
takes precedence over previous ones. As for the simpler LWW
type, the value
type V
is also required to implement the CRDT trait.
We do not encourage mutating the values associated with a given key
without updating the timestamp, in fact at the moment we do not provide a .get_mut()
method that would allow that.
Internally, the map is stored as a vector of keys and values, sorted by ascending key order.
This is why the key type K
must implement Ord
(and also to ensure a unique serialization,
such that two values can be compared for equality based on their hashes). As a consequence,
insertions take O(n)
time. This means that LWWMap should be used for reasonably small maps.
However, note that even if we were using a more efficient data structure such as a BTreeMap
,
the serialization cost O(n)
would still have to be paid at each modification, so we are
actually not losing anything here.
Implementations
impl<K, V> LwwMap<K, V> where
K: Ord,
V: Crdt,
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impl<K, V> LwwMap<K, V> where
K: Ord,
V: Crdt,
[src]pub fn migrate_from_raw_item(k: K, ts: u64, v: V) -> Self
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pub fn migrate_from_raw_item(k: K, ts: u64, v: V) -> Self
[src]Used to migrate from a map defined in an incompatible format. This produces a map that contains a single item with the specified timestamp (copied from the incompatible format). Do this as many times as you have items to migrate, and put them all together using the CRDT merge operator.
pub fn update_mutator(&self, k: K, new_v: V) -> Self
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pub fn update_mutator(&self, k: K, new_v: V) -> Self
[src]Returns a map that contains a single mapping from the specified key to the specified value. This map is a mutator, or a delta-CRDT, such that when it is merged with the original map, the previous value will be replaced with the one specified here. The timestamp in the provided mutator is set to the maximum of the current system’s clock and 1 + the previous value’s timestamp (if there is one), so that the new value will always take precedence (LWW rule).
Typically, to update the value associated to a key in the map, you would do the following:
let my_update = my_crdt.update_mutator(key_to_modify, new_value); my_crdt.merge(&my_update);
However extracting the mutator on its own and only sending that on the network is very interesting as it is much smaller than the whole map.
pub fn take_and_clear(&mut self) -> Self
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pub fn take_and_clear(&mut self) -> Self
[src]Takes all of the values of the map and returns them. The current map is reset to the empty map. This is very usefull to produce in-place a new map that contains only a delta that modifies a certain value:
let mut a = get_my_crdt_value(); let old_a = a.take_and_clear(); a.merge(&old_a.update_mutator(key_to_modify, new_value)); put_my_crdt_value(a);
Of course in this simple example we could have written simply
pyt_my_crdt_value(a.update_mutator(key_to_modify, new_value))
,
but in the case where the map is a field in a struct for instance (as is always the case),
this becomes very handy:
let mut a = get_my_crdt_value(); let old_a_map = a.map_field.take_and_clear(); a.map_field.merge(&old_a_map.update_mutator(key_to_modify, new_value)); put_my_crdt_value(a);
Trait Implementations
impl<'de, K, V> Deserialize<'de> for LwwMap<K, V> where
K: Deserialize<'de>,
V: Deserialize<'de>,
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impl<'de, K, V> Deserialize<'de> for LwwMap<K, V> where
K: Deserialize<'de>,
V: Deserialize<'de>,
[src]fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
__D: Deserializer<'de>,
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fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
__D: Deserializer<'de>,
[src]Deserialize this value from the given Serde deserializer. Read more
impl<K, V> StructuralPartialEq for LwwMap<K, V>
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Auto Trait Implementations
impl<K, V> RefUnwindSafe for LwwMap<K, V> where
K: RefUnwindSafe,
V: RefUnwindSafe,
K: RefUnwindSafe,
V: RefUnwindSafe,
impl<K, V> Send for LwwMap<K, V> where
K: Send,
V: Send,
K: Send,
V: Send,
impl<K, V> Sync for LwwMap<K, V> where
K: Sync,
V: Sync,
K: Sync,
V: Sync,
impl<K, V> Unpin for LwwMap<K, V> where
K: Unpin,
V: Unpin,
K: Unpin,
V: Unpin,
impl<K, V> UnwindSafe for LwwMap<K, V> where
K: UnwindSafe,
V: UnwindSafe,
K: UnwindSafe,
V: UnwindSafe,
Blanket Implementations
impl<T> BorrowMut<T> for T where
T: ?Sized,
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impl<T> BorrowMut<T> for T where
T: ?Sized,
[src]pub fn borrow_mut(&mut self) -> &mut T
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pub fn borrow_mut(&mut self) -> &mut T
[src]Mutably borrows from an owned value. Read more
impl<T> Instrument for T
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impl<T> Instrument for T
[src]fn instrument(self, span: Span) -> Instrumented<Self>
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fn instrument(self, span: Span) -> Instrumented<Self>
[src]Instruments this type with the provided Span
, returning an
Instrumented
wrapper. Read more
fn in_current_span(self) -> Instrumented<Self>
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fn in_current_span(self) -> Instrumented<Self>
[src]impl<T> Pointable for T
impl<T> Pointable for T
impl<T> Same<T> for T
impl<T> Same<T> for T
type Output = T
type Output = T
Should always be Self
impl<T> ToOwned for T where
T: Clone,
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impl<T> ToOwned for T where
T: Clone,
[src]type Owned = T
type Owned = T
The resulting type after obtaining ownership.
pub fn to_owned(&self) -> T
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pub fn to_owned(&self) -> T
[src]Creates owned data from borrowed data, usually by cloning. Read more
pub fn clone_into(&self, target: &mut T)
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pub fn clone_into(&self, target: &mut T)
[src]🔬 This is a nightly-only experimental API. (toowned_clone_into
)
recently added
Uses borrowed data to replace owned data, usually by cloning. Read more
impl<V, T> VZip<V> for T where
V: MultiLane<T>,
impl<V, T> VZip<V> for T where
V: MultiLane<T>,
pub fn vzip(self) -> V
impl<T> DeserializeOwned for T where
T: for<'de> Deserialize<'de>,
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T: for<'de> Deserialize<'de>,