Struct VectorScanConfig 

pub struct VectorScanConfig {
    pub hnsw: HnswIterativeScan,
    pub ivfflat: IvfflatIterativeScan,
    pub ef_search: Option<u32>,
}

pgvector scan settings applied to every connection a pool opens (#1116).

Lowered into the PostgreSQL startup options packet for the same reason SearchPath is: a pooled SET configures one session out of N, and misses every connection the pool opens later. Riding the startup packet costs no round trip and survives DISCARD ALL.

⚠ Safe on a database without pgvector. A two-part GUC name is accepted as a placeholder when no extension has claimed it, so the connection succeeds and the value simply never takes effect — verified against a database with the extension absent. The same mechanism covers a pgvector older than 0.8, which defines neither GUC.

Fields

hnsw: HnswIterativeScan

hnsw.iterative_scan.

ivfflat: IvfflatIterativeScan

ivfflat.iterative_scan.

ef_search: Option<u32>

hnsw.ef_search, or None to leave pgvector’s default of 40.

⚠ iterative_scan alone does not guarantee k rows, and on some corpora it is not even the binding constraint. Measured on this repository’s rig — 20 000 rows × 64 dimensions of uniform-random vectors, a filter matching 1%, k = 10, three independently generated datasets:

configuration	rows returned
iterative_scan=off (pgvector’s default)	2, 3, 4
iterative_scan=strict_order, other GUCs default	10, 5, 4
…plus max_scan_tuples raised 100×	10, 5, 4 — no change
…plus ef_search=1000 instead	10, 10, 10
iterative_scan=off and ef_search=1000	10, 10, 10

So ef_search — the size of the candidate list the graph search keeps — is what decides whether ten members of a 1% subset are found at all, and max_scan_tuples (which #1314 was filed against) changed nothing. Uniform-random high-dimensional vectors are the adversarial case, and the benchmark in benches/vector_filtered_ann.sql reports recall 1.00 from iterative_scan alone on its own corpus — which is the point: which knob binds depends on the data, so both have to be reachable.

Left unset by default deliberately. iterative_scan costs nothing on an unfiltered search (measured: recall already 1.000, timings tie), so naming it is free. ef_search is a latency/recall trade paid by every search on the deployment, filtered or not, and its right value is a property of the corpus. FraiseQL will not choose it for an operator; it makes it reachable and says, above, how to tell that it is the one to reach for.

Implementations

impl VectorScanConfig

pub fn startup_fragments(self) -> Vec<String>

The -c fragments these settings contribute to the startup packet.

Empty when both are Off — an operator who turned the feature off gets pgvector’s own default rather than an explicit off, so the server’s or the database’s own ALTER DATABASE setting still applies. Writing -c hnsw.iterative_scan=off would override such a setting, which is not what “leave it alone” means.

Trait Implementations

impl Clone for VectorScanConfig

fn clone(&self) -> VectorScanConfig

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for VectorScanConfig

impl Debug for VectorScanConfig

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

Formats the value using the given formatter.

impl Default for VectorScanConfig

fn default() -> VectorScanConfig

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for VectorScanConfig

fn deserialize<__D>( __deserializer: __D, ) -> Result<VectorScanConfig, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for VectorScanConfig

impl PartialEq for VectorScanConfig

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

Equality operator ==.

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

Inequality operator !=.

impl Serialize for VectorScanConfig

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for VectorScanConfig