Enum FilterStrategy 

pub enum FilterStrategy {
    PostFilter {
        oversample: f32,
    },
    PreFilter,
    Hybrid {
        oversample_min: f32,
        oversample_max: f32,
    },
    Auto,
}

Strategy for combining filtering with HNSW search.

Variants

Variant	Description	When to Use
PostFilter	Search first, filter results	Low selectivity (<5%)
PreFilter	Filter first, search subset	High selectivity (>80%)
Hybrid	Adaptive oversample	Medium selectivity
Auto	Automatic selection	Default; estimates selectivity

Variants

PostFilter

Post-filter with fixed oversample factor.

Retrieves k × oversample candidates from HNSW, then filters. Best for low selectivity (few vectors pass filter).

Fields

oversample: f32

Oversample factor (1.0 = no oversampling, 10.0 = max).

PreFilter

Pre-filter (full metadata scan, then search on subset).

Scans all metadata to find matching vectors, then searches only the matching subset. Best for high selectivity (most pass).

Hybrid

Hybrid with bounded oversample (adaptive based on selectivity).

Estimates selectivity via sampling, then calculates appropriate oversample within the given bounds.

Fields

oversample_min: f32

Minimum oversample (floor).

oversample_max: f32

Maximum oversample (ceiling).

Auto

Automatic strategy selection based on estimated selectivity.

Samples vectors to estimate selectivity, then selects the appropriate strategy (PreFilter, PostFilter, or Hybrid).

Implementations

impl FilterStrategy

pub const POST_FILTER_DEFAULT: Self

Post-filter with default oversample (3x).

pub const HYBRID_DEFAULT: Self

Hybrid with default bounds (1.5x to 10x).

pub fn validate(&self) -> Result<(), FilterError>

Validate strategy configuration.

Errors

Returns FilterError::InvalidStrategy if:

• PostFilter.oversample < 1.0 or > MAX_OVERSAMPLE
• Hybrid.oversample_min < 1.0
• Hybrid.oversample_max < oversample_min
• Hybrid.oversample_max > MAX_OVERSAMPLE

Trait Implementations

impl Clone for FilterStrategy

fn clone(&self) -> FilterStrategy

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for FilterStrategy

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

Formats the value using the given formatter.

impl Default for FilterStrategy

fn default() -> FilterStrategy

Returns the “default value” for a type.

impl PartialEq for FilterStrategy

fn eq(&self, other: &FilterStrategy) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for FilterStrategy

impl StructuralPartialEq for FilterStrategy