Struct PresenceAndLFUFilter 

pub struct PresenceAndLFUFilter<Src: BlockMetadata, Dst: BlockMetadata> { /* private fields */ }

G2→G3 filter: presence check + LFU count threshold.

Combines two filter conditions:

1. Skip blocks already present in destination tier
2. Only offload blocks with LFU count above threshold

The LFU threshold ensures we only offload “hot” blocks that have been accessed frequently, avoiding wasted transfers for rarely-used blocks.

Duplicate Prevention

When a PendingTracker is configured, this filter also checks for blocks that are currently in-flight through the pipeline.

Performance

This policy is fully synchronous and returns Either::Left(Ready), avoiding any heap allocation per evaluation.

Example

// Only offload blocks with LFU count > 8 that aren't in G3 or in-flight
let tracker = Arc::new(PendingTracker::new());
let filter = PresenceAndLFUFilter::<G2, G3>::new(registry.clone(), 8)
    .with_pending_tracker(tracker);

Implementations

impl<Src: BlockMetadata, Dst: BlockMetadata> PresenceAndLFUFilter<Src, Dst>

pub fn new(registry: Arc<BlockRegistry>, min_lfu_count: u32) -> Self

Create a new presence + LFU filter with specified threshold.

pub fn with_default_threshold(registry: Arc<BlockRegistry>) -> Self

Create with default threshold of 8.

pub fn with_pending_tracker(self, tracker: Arc<PendingTracker>) -> Self

Add a pending tracker for duplicate prevention.

Trait Implementations

impl<Src: BlockMetadata, Dst: BlockMetadata> OffloadPolicy<Src> for PresenceAndLFUFilter<Src, Dst>

fn name(&self) -> &str

Unique name for this policy (for logging/debugging).

fn evaluate<'a>(&'a self, ctx: &'a EvalContext<Src>) -> PolicyFuture<'a>

Evaluate whether a block should be offloaded.

fn evaluate_batch<'a>( &'a self, contexts: &'a [EvalContext<Src>], ) -> PolicyBatchFuture<'a>

Batch evaluate multiple blocks.