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/// Storage tier classification.
///
/// Data flows downward: L0 → L1 → L2 as it ages and cools.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum StorageTier {
/// L0 (Hot): Lock-free radix trees, memtables, active CRDT states.
/// Pure RAM — no I/O.
L0Ram,
/// L1 (Warm): HNSW graphs, metadata indexes, segment files.
/// NVMe via mmap + madvise(MADV_WILLNEED).
/// Zero-copy deserialization, SIMD reads directly from mmap.
L1Nvme,
/// L2 (Cold): Historical logs, compressed vector layers.
/// Remote object storage (S3/GCS), Parquet-encoded.
/// DataFusion predicate pushdown for minimal egress.
L2Remote,
}
impl StorageTier {
/// Whether this tier is memory-resident (no I/O needed).
pub fn is_memory_resident(self) -> bool {
matches!(self, StorageTier::L0Ram)
}
/// Whether this tier uses mmap (potential page faults on TPC cores).
pub fn uses_mmap(self) -> bool {
matches!(self, StorageTier::L1Nvme)
}
/// Whether this tier requires network I/O.
pub fn is_remote(self) -> bool {
matches!(self, StorageTier::L2Remote)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn tier_properties() {
assert!(StorageTier::L0Ram.is_memory_resident());
assert!(!StorageTier::L0Ram.uses_mmap());
assert!(!StorageTier::L0Ram.is_remote());
assert!(!StorageTier::L1Nvme.is_memory_resident());
assert!(StorageTier::L1Nvme.uses_mmap());
assert!(!StorageTier::L1Nvme.is_remote());
assert!(!StorageTier::L2Remote.is_memory_resident());
assert!(!StorageTier::L2Remote.uses_mmap());
assert!(StorageTier::L2Remote.is_remote());
}
}