Enum mz_storage::controller::ReadPolicy

pub enum ReadPolicy<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

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 ReadPolicy<Timestamp>

pub fn lag_writes_by(lag: Timestamp) -> Self

Creates a read policy that lags the write frontier by the indicated amount, rounded down to a multiple of that amount.

The rounding down is done to reduce the number of changes the capability undergoes, with the thinking being that if you are ok with lag, then getting something between lag and 2 x lag should be ok.

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.