pub struct QueryCache { /* private fields */ }Expand description
Bounded query cache for parsed VelesQL queries (issue #903).
Thread-safe implementation using parking_lot::RwLock.
§Design notes
- Canonical query text is hashed for compact bucketing.
- Hash collisions are handled explicitly via a per-bucket vector, with a strict equality check on the original query text before reuse.
- Parsed ASTs are stored behind
Arc<Query>; a hit returnsArc::clone(a refcount bump) instead of deep-cloning the AST. - A live
usizesize counter (AtomicUsize) gives O(1)len()and avoids re-summing every bucket on each insert/eviction.
§Hot-path concurrency (issue #903)
The previous design took a global write lock (order.write()) on every
cache hit to promote the entry to the MRU position, serialising all reads.
This implementation replaces strict LRU with a CLOCK / second-chance
policy:
- A cache hit takes only a shared
read()lock and sets a per-entryreferencedbit via a relaxed atomic store — no write lock, so concurrent hits run in parallel. - Eviction (on the cold insert path, under the write lock) sweeps the
insertion-order ring: an entry whose
referencedbit is set gets a second chance (bit cleared, moved to the back); an entry with a clear bit is evicted. This approximates LRU while keeping the hit path lock-light.
Implementations§
Source§impl QueryCache
impl QueryCache
Sourcepub fn new(max_size: usize) -> Self
pub fn new(max_size: usize) -> Self
Creates a new query cache with the specified maximum size.
§Arguments
max_size- Maximum number of queries to cache (minimum 1).
Sourcepub fn parse(&self, query: &str) -> Result<Arc<Query>, ParseError>
pub fn parse(&self, query: &str) -> Result<Arc<Query>, ParseError>
Parses a query, returning a shared (Arc) cached AST if available.
§Errors
Returns ParseError if the query is invalid.
Sourcepub fn stats(&self) -> CacheStats
pub fn stats(&self) -> CacheStats
Returns current cache statistics.
Trait Implementations§
Auto Trait Implementations§
impl !Freeze for QueryCache
impl !RefUnwindSafe for QueryCache
impl Send for QueryCache
impl Sync for QueryCache
impl Unpin for QueryCache
impl UnsafeUnpin for QueryCache
impl UnwindSafe for QueryCache
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