inillucent_sql/bind/
column_use.rs

1//! What a query reads of one FROM term, which decides whether an index covers it.
2//!
3//! Invariant: **a `ColumnUse` that cannot list every read says so with `opaque`, and an opaque
4//! answer is never covered.** The planner reads an index instead of the table only when every
5//! slot the query needs is in the index, so a read missed here is a column read from an index
6//! that does not hold it.
7
8use super::BoundExpr;
9
10/// Which of one FROM term's columns a query reads.
11#[derive(Clone, Debug, Default, PartialEq)]
12pub struct ColumnUse {
13    /// The record slots read, ascending and without duplicates.
14    pub columns: Vec<u16>,
15    /// Whether the term's rowid is read.
16    pub rowid: bool,
17    /// Whether something was met whose column reads cannot be enumerated.
18    ///
19    /// An opaque use is never coverable. It is set rather than ignored because
20    /// the whole value of this answer is that it is complete: a covering path
21    /// that turned out not to cover a column would read it from an index that
22    /// does not hold it.
23    pub opaque: bool,
24    /// The module's auxiliary functions this term is asked for, in the order
25    /// they were met, as a folded name and the arguments after the table.
26    ///
27    /// `score(t)` and `bm25(t)` read the *cursor* rather than a column, so they
28    /// are neither a column read nor an opaque one: the module can answer them
29    /// per row, and a materialised virtual scan carries the answers beside the
30    /// columns. Recorded here because this is already the answer to "what does
31    /// this term have to produce", and a second list would be a second thing
32    /// that can disagree with it.
33    /// **The arguments, not their count.** `highlight(t, 0, '[', ']')` and
34    /// `bm25(t, 10.0, 1.0)` are answered by the module from the cursor, and the
35    /// module cannot answer either without the values - which used to be
36    /// dropped here and replaced with an empty list at the call, so every
37    /// auxiliary function saw no arguments at all. Two calls of one name with
38    /// different arguments are also two different answers, so the arguments are
39    /// part of what identifies a slot rather than a detail hanging off one.
40    pub functions: Vec<(Vec<u8>, Vec<BoundExpr>)>,
41    /// The record slots read by anything other than the block's `WHERE` clause.
42    ///
43    /// A partial index whose predicate the `WHERE` repeats holds that predicate true for every
44    /// entry, so a column the `WHERE` reads only for that test does not have to be in the index
45    /// for the index to cover the query. This is the part of `columns` that is read for other
46    /// reasons.
47    pub outside_filter: Vec<u16>,
48}
49
50impl ColumnUse {
51    /// Records that one slot is read.
52    pub fn add(&mut self, slot: u16) {
53        if let Err(position) = self.columns.binary_search(&slot) {
54            self.columns.insert(position, slot);
55        }
56    }
57
58    /// Records that one of the module's auxiliary functions is read.
59    ///
60    /// @param name - the function's folded name
61    /// @param arguments - the arguments after the table
62    pub fn add_function(&mut self, name: &[u8], arguments: &[BoundExpr]) {
63        let held = (name.to_vec(), arguments.to_vec());
64        if !self.functions.contains(&held) {
65            self.functions.push(held);
66        }
67    }
68
69    /// Folds another use into this one.
70    pub fn merge(&mut self, other: &ColumnUse) {
71        for slot in &other.columns {
72            self.add(*slot);
73        }
74        self.rowid |= other.rowid;
75        self.opaque |= other.opaque;
76        for slot in &other.outside_filter {
77            if let Err(position) = self.outside_filter.binary_search(slot) {
78                self.outside_filter.insert(position, *slot);
79            }
80        }
81        for (name, arguments) in &other.functions {
82            self.add_function(name, arguments);
83        }
84    }
85}
inillucent_sql/bind/column_use.rs

inillucent_sql/bind/
column_use.rs
