Enum mz_storage_types::read_policy::ReadPolicy

pub enum ReadPolicy<T> {
    NoPolicy {
        initial_since: Antichain<T>,
    },
    ValidFrom(Antichain<T>),
    LagWriteFrontier(Arc<dyn Fn(AntichainRef<'_, T>) -> Antichain<T> + Send + Sync>),
    Multiple(Vec<ReadPolicy<T>>),
}

Compaction policies for collections maintained by Controller.

NOTE(benesch): this might want to live somewhere besides the storage crate, because it is fundamental to both storage and compute.

Variants

NoPolicy

No-one has yet requested a ReadPolicy from us, which means that we can still change the implied_capability/the collection since if we need to.

Fields

initial_since: Antichain<T>

ValidFrom(Antichain<T>)

Maintain the collection as valid from this frontier onward.

LagWriteFrontier(Arc<dyn Fn(AntichainRef<'_, T>) -> Antichain<T> + Send + Sync>)

Maintain the collection as valid from a function of the write frontier.

This function will only be re-evaluated when the write frontier changes. If the intended behavior is to change in response to external signals, consider using the ValidFrom variant to manually pilot compaction.

The Arc makes the function cloneable.

Multiple(Vec<ReadPolicy<T>>)

Allows one to express multiple read policies, taking the least of the resulting frontiers.

Implementations

impl<T> ReadPolicy<T>

where T: Timestamp + TimestampManipulation,

pub fn step_back() -> Self

Creates a read policy that lags the write frontier “by one”.

impl ReadPolicy<Timestamp>

pub fn lag_writes_by(lag: Timestamp, max_granularity: Timestamp) -> Self

Creates a read policy that lags the write frontier by the indicated amount, rounded down to (at most) the specified value. The rounding down is done to reduce the number of changes the capability undergoes.

impl<T: Timestamp> ReadPolicy<T>

pub fn frontier(&self, write_frontier: AntichainRef<'_, T>) -> Antichain<T>

Trait Implementations

impl<T: Clone> Clone for ReadPolicy<T>

fn clone(&self) -> ReadPolicy<T>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T> Debug for ReadPolicy<T>

where T: Debug,

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

Formats the value using the given formatter.

impl<T> Serialize for ReadPolicy<T>

where T: Serialize,

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

where __S: Serializer,

Serialize this value into the given Serde serializer.