Crate mz_transform

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

analysis

Traits and types for reusable expression analysis

canonicalization

Transformations that bring relation expressions to their canonical form.

canonicalize_mfp

Canonicalizes MFPs, e.g., performs CSE on the scalar expressions, eliminates identity MFPs.

column_knowledge

Transformations based on pulling information about individual columns from sources.

compound

Transformations that don’t fit into one of the canonicalization, fusion, movement, or ordering buckets.

cse

Common subexpression elimination.

dataflow

Whole-dataflow optimization

demand

Transformation based on pushing demand information about columns toward sources.

equivalence_propagation

Propagates expression equivalence from leaves to root, and back down again.

fold_constants

Replace operators on constants collections with constant collections.

fusion

Transformations that fuse together others of their kind.

join_implementation

Determines the join implementation for join operators.

literal_constraints

See if there are predicates of the form <expr> = literal that can be sped up using an index. More specifically, look for an MFP on top of a Get, where the MFP has an appropriate filter, and the Get has a matching index. Convert these to IndexedFilter joins, which is a semi-join with a constant collection.

literal_lifting

Hoist literal values from maps wherever possible.

monotonic

Analysis to identify monotonic collections, especially TopK inputs.

movement

Transformations that move relation expressions up (lifting) and down (pushdown) the tree.

non_null_requirements

Push non-null requirements toward sources.

normalize_lets

Normalize the structure of Let and LetRec operators in expressions.

normalize_ops

Normalize the structure of various operators.

notice

Notices that the optimizer wants to show to users.

ordering

Transformations that impose a canonical order on the inputs of multi-input relation expressions.

predicate_pushdown

Pushes predicates down through other operators.

reduce_elision

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

reduce_reduction

Breaks complex Reduce variants into a join of simpler variants.

reduction_pushdown

Tries to convert a reduce around a join to a join of reduces. Also absorbs Map operators into Reduce operators.

redundant_join

Remove redundant collections of distinct elements from joins.

semijoin_idempotence

Remove semijoins that are applied multiple times to no further effect.

threshold_elision

Remove Threshold operators when we are certain no records have negative multiplicity.

typecheck

Check that the visible type of each query has not been changed

union_cancel

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

will_distinct

Transform that pushes down the information that a collection will be subjected to a Distinct on specific columns.

Macros

all

Compute the conjunction of a variadic number of expressions.

any

Compute the disjunction of a variadic number of expressions.

transforms 🔒

Convenience macro for guarding transforms behind a feature flag.

Structs

EmptyIndexOracle

An IndexOracle that knows about no indexes.

EmptyStatisticsOracle

A StatisticsOracle that knows nothing and can give no estimates.

Fixpoint

A sequence of transformations iterated some number of times.

FuseAndCollapse

A sequence of transformations that simplify the MirRelationExpr

Optimizer

A naive optimizer for relation expressions.

TransformCtx

Arguments that get threaded through all transforms, plus a DataflowMetainfo that can be manipulated by the transforms.

Enums

TransformError

Errors that can occur during a transformation.

Constants

FOLD_CONSTANTS_LIMIT 🔒

Traits

IndexOracle

A trait for a type that can answer questions about what indexes exist.

MaybeShouldPanic

Implemented by error types that sometimes want to indicate that an error should cause a panic even in a catch_unwind context. Useful for implementing mz_unsafe.mz_panic('forced panic').

StatisticsOracle

A trait for a type that can estimate statistics about a given GlobalId

Transform

Types capable of transforming relation expressions.

Functions

catch_unwind_optimize

Catch panics in the given optimization, and demote them to TransformError::Internal error.

fold_constants_fixpoint

Does constant folding to a fixpoint: An expression all of whose leaves are constants, of size small enough to be inlined and folded should reach a single MirRelationExpr::Constant.

fuse_and_collapse_fixpoint

Run the FuseAndCollapse transforms in a fixpoint.

normalize

Construct a normalizing transform that runs transforms that normalize the structure of the tree until a fixpoint.