Enum Query

pub enum Query<'a, K: Key + LayerKey + OrdLowerBound> {
    Point(&'a K),
    LimitedRange(&'a K),
    FullRange(&'a K),
    FullScan,
}

Query describes the goal of a search in the LSM tree. The caller specifies this to guide the merger on which layer files it must consult. Layers might be skipped during a query for a few reasons:

• Existence filters might allow layer files to be skipped.
• For bounded queries (i.e. any except FullScan), if the search key has MergeType::OptimizedMerge, we can use that to omit older layers once we find a match.

Variants

Point(&'a K)

Point queries look for a specific key in the LSM tree. In this case, the existence filters for each layer file can be used to decide if the layer file needs to be consulted. Note that it is an error to use Point for range-like keys. Either LimitedRange or FullRange must be used instead.

LimitedRange(&'a K)

LimitedRange queries position the iterator to K::search_key, and scans forward until the first record which does not overlap the provided key. In this case, the existence filters for each layer file can be used, but we have to check for all possible keys in the range we wish to search. Obviously, that means that the range should be, well, limited. Fuzzy hashes permit this for extent-like keys, but these queries are not the right choice for things like searching a directory.

FullRange(&'a K)

FullRange queries position the iterator to a starting key, and scan forward to the first key of a different type. In this case, the existence filters are not used.

FullScan

FullScan queries are intended to yield every record in the tree. In this case, the existence filters are not used.

Trait Implementations

impl<'a, K: Clone + Key + LayerKey + OrdLowerBound> Clone for Query<'a, K>

fn clone(&self) -> Query<'a, K>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<'a, K: Debug + Key + LayerKey + OrdLowerBound> Debug for Query<'a, K>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.