Struct PermutationsSignal 

pub struct PermutationsSignal {
    pub count: u8,
    pub names: Vec<String>,
    pub merge_join: bool,
}

The file’s index permutation set: how many orders of (s, p, o) it stores, and therefore whether its planner can run a sort-merge join.

rete build --permutations 3 writes SPO, POS and OSP only. Those three tie the longest bound prefix on all eight triple-pattern shapes, so the file answers every query with the same rows, routed to the same tiles — the difference is invisible from the results, exactly like a missing full-text index (#189). What it gives up is the merge join: SOP/PSO/OPS exist only to hand a join two streams already sorted on the join key, and they are typically ~40% of a built file. A consumer choosing between two mirrors of one dataset, or deciding whether a join-heavy workload will hold up, has to be able to see which it has.

Measured at read time, never stored, for the reasons TextIndexSignal spells out and one more that is specific to this signal: which permutations a file carries is a fact about its bytes. A stored copy would be an authored claim about the file’s own layout — the one class of statement the file can always check for itself, in the 1 KiB header every card read has already fetched. This costs no extra read at all.

Fields

count: u8

How many permutations are stored: 3 or 6 today.

names: Vec<String>

Their names in section order, e.g. ["SPO", "POS", "OSP"]. Written out rather than implied by count, because the mask is a set and a future build may keep a different three.

merge_join: bool

Whether the file carries the merge-join orders (SOP, PSO, OPS) — i.e. whether a two-pattern join sharing a same-role variable can be answered by a linear two-pointer merge instead of a hash join.

Implementations

impl PermutationsSignal

pub fn probe(header: &Header) -> Self

Read it straight off the parsed header — the mask is one byte at [50], and 0 there means all six (every file written before the mask existed). No range read of any kind.

pub fn describe(&self) -> String

One line for the human catalog view and the audit report.

Trait Implementations

impl Clone for PermutationsSignal

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for PermutationsSignal

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for PermutationsSignal

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Eq for PermutationsSignal

impl PartialEq for PermutationsSignal

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

Equality operator ==.

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

Inequality operator !=.

impl Serialize for PermutationsSignal

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

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for PermutationsSignal