Struct transform::map_lifting::LiteralLifting [−][src]
pub struct LiteralLifting {
recursion_guard: RecursionGuard,
}
Expand description
Hoist literal values from maps wherever possible.
Fields
recursion_guard: RecursionGuard
Implementations
pub fn action(
&self,
relation: &mut MirRelationExpr,
gets: &mut HashMap<Id, Vec<MirScalarExpr>>
) -> Result<Vec<MirScalarExpr>, TransformError>
pub fn action(
&self,
relation: &mut MirRelationExpr,
gets: &mut HashMap<Id, Vec<MirScalarExpr>>
) -> Result<Vec<MirScalarExpr>, TransformError>
Hoist literal values from maps wherever possible.
Returns a list of literal scalar expressions that must be appended
to the result before it can be correctly used. The intent is that
this action extracts a maximal set of literals from relation
,
which can then often be propagated further up and inlined in any
expressions as it goes.
In several cases, we only manage to extract literals from the final columns. But in those cases where it is possible, permutations are used to move all of the literals to the final columns, and then rely on projection hoisting to allow the these literals to move up the AST.
TODO: The literals from the final columns are returned as the result of this method, whereas literals in intermediate columns are extracted using permutations. The reason for this different treatment is that in some cases it is not possible to remove the projection of the permutation, preventing the lifting of a literal that could otherwise be lifted, the following example being of them:
%0 = | Constant (1, 2, 3) (2, 2, 3)
%1 = | Constant (4, 3, 3) (4, 5, 3)
%2 = | Union %0 %1
If final literals weren’t treated differently, the example above would lead to the following transformed plan:
%0 = | Constant (1) (2) | Map 2, 3 | Project (#0..#2)
%1 = | Constant (3) (5) | Map 4, 3 | Project (#1, #0, #2)
%2 = | Union %0 %1
Since the union branches have different projections, they cannot be removed, preventing literal 3 from being lifted further.
In theory, all literals could be treated in the same way if this method returned both a list of literals and a projection vector, making the caller have to deal with the reshuffling. (see https://github.com/MaterializeInc/materialize/issues/6598)
Trait Implementations
Extracts a reference to the recursion guard embedded within the type.
fn checked_recur<F, T, E>(&self, f: F) -> Result<T, E> where
F: FnOnce(&Self) -> Result<T, E>,
E: From<RecursionLimitError>,
fn checked_recur<F, T, E>(&self, f: F) -> Result<T, E> where
F: FnOnce(&Self) -> Result<T, E>,
E: From<RecursionLimitError>,
Checks whether it is safe to recur and calls f
if so. Read more
fn checked_recur_mut<F, T, E>(&mut self, f: F) -> Result<T, E> where
F: FnOnce(&mut Self) -> Result<T, E>,
E: From<RecursionLimitError>,
fn checked_recur_mut<F, T, E>(&mut self, f: F) -> Result<T, E> where
F: FnOnce(&mut Self) -> Result<T, E>,
E: From<RecursionLimitError>,
Like CheckedRecursion::checked_recur
, but operates on a mutable
reference to Self
. Read more
Returns the “default value” for a type. Read more
fn transform(
&self,
relation: &mut MirRelationExpr,
_: TransformArgs<'_>
) -> Result<(), TransformError>
fn transform(
&self,
relation: &mut MirRelationExpr,
_: TransformArgs<'_>
) -> Result<(), TransformError>
Transform a relation into a functionally equivalent relation.
Auto Trait Implementations
impl !RefUnwindSafe for LiteralLifting
impl Send for LiteralLifting
impl !Sync for LiteralLifting
impl Unpin for LiteralLifting
impl UnwindSafe for LiteralLifting
Blanket Implementations
Mutably borrows from an owned value. Read more
Attaches the provided Subscriber
to this type, returning a
WithDispatch
wrapper. Read more
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more