# Crate transform[−][src]

## Expand description

Transformations for relation expressions.

This crate contains traits, types, and methods suitable for transforming
`MirRelationExpr`

types in ways that preserve semantics and improve performance.
The core trait is `Transform`

, and many implementors of this trait can be
boxed and iterated over. Some common transformation patterns are wrapped
as `Transform`

implementors themselves.

The crate also contains the beginnings of whole-dataflow optimization, which uses the same analyses but spanning multiple dataflow elements.

## Re-exports

`pub use dataflow::optimize_dataflow;`

## Modules

Canonicalizes MFPs and performs common sub-expression elimination.

Transformations based on pulling information about individual columns from sources.

Common subexpression elimination.

Whole-dataflow optimization

Transformation based on pushing demand information about columns toward sources.

Transformations that fuse together others of their kind.

Install replace certain `Get`

operators with their `Let`

value.

Determines the join implementation for join operators.

Hoist literal values from maps wherever possible.

Push non-null requirements toward sources.

Harvests information about non-nullability of columns from sources.

Pushes predicates down through other operators.

Transform column references in a `Map`

into a `Project`

.

Hoist projections through operators.

Pushes column removal down through other operators.

Removes `Reduce`

when the input has as unique keys the keys of the reduce.

Replace operators on constants collections with constant collections.

Preliminary work on reduction push-down.

Remove redundant collections of distinct elements from joins.

Remove TopK operators with both an offset of zero and no limit.

Detects an input being unioned with its negation and cancels them out

Re-assign type information and identifiers to each `Get`

to ensure
uniqueness of identifiers.

## Structs

A sequence of transformations iterated some number of times.

A sequence of transformations that simplify the `MirRelationExpr`

A naive optimizer for relation expressions.

Arguments that get threaded through all transforms.

## Enums

Errors that can occur during a transformation.

## Traits

Types capable of transforming relation expressions.