abhita opened a new issue, #18405:
URL: https://github.com/apache/datafusion/issues/18405
Currently for a given Cache like `DefaultFilesMetadataCache`, all the Cache
Storage and Retrieval mechanisms are tightly coupled with Eviction Strategy.
```
struct DefaultFilesMetadataCacheState {
lru_queue: LruQueue<Path, (ObjectMeta, Arc<dyn FileMetadata>)>,
memory_limit: usize,
memory_used: usize,
cache_hits: HashMap<Path, usize>,
}
```
For any change in Eviction Policy strategy, we would have to end up
implementing a new DataStructure having its' own implementation of Cache
Accessing methods.
Instead, we can decouple the Cache Data Structure and the Eviction
Strategies by doing something similar as below:
```
pub struct FileMetadataCache {
/// (DashMap-based, already thread-safe)
inner_cache: DashMap<ObjectMeta, FileMetadata>,
/// The eviction policy (thread-safe)
eviction_strategy: Arc<Mutex<Box<dyn EvictionStrategy>>>,
.
.
.
.
```
Accompanied by a pluggable Cache Strategy which would be listening to events
from Cache-Storage and accordingly select items of eviction
```
// Core trait for cache eviction strategy
pub trait EvictionStrategy: Send + Sync {
/// Called when a cache entry is accessed
fn on_access(&mut self, key: &str, size: usize);
/// Called when a cache entry is inserted
fn on_insert(&mut self, key: &str, size: usize);
/// Called when a cache entry is removed
fn on_remove(&mut self, key: &str);
/// Select entries for eviction to reach target size
/// Returns keys to evict, ordered by eviction priority
fn select_for_eviction(&self, target_size: usize) -> Vec<String>;
/// Reset policy state
fn clear(&mut self);
/// Get the name of this strategy
fn strategy_name(&self) -> &'static str;
}
```
Benefits
- Separation of Concerns: Cache storage logic is independent of eviction
policy
- Strategy Hot-Swapping: Change eviction strategies without recompiling the
cache
- Multiple Implementations: Support LRU, LFU, FIFO, ARC, LIRS, or custom
strategies out-of-the-box
- Per-Cache Policies and Code Re-usability: Different cache instances can
use different strategies
- Reduced Duplication: Eliminate duplicated cache access code across
implementations
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
