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pruning.rs
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pruning.rs
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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied. See the License for the
// specific language governing permissions and limitations
// under the License.
//! [`PruningPredicate`] to apply filter [`Expr`] to prune "containers"
//! based on statistics (e.g. Parquet Row Groups)
//!
//! [`Expr`]: crate::prelude::Expr
use std::collections::HashSet;
use std::convert::TryFrom;
use std::sync::Arc;
use crate::{
common::{Column, DFSchema},
error::{DataFusionError, Result},
logical_expr::Operator,
physical_plan::{ColumnarValue, PhysicalExpr},
};
use arrow::record_batch::RecordBatchOptions;
use arrow::{
array::{new_null_array, ArrayRef, BooleanArray},
datatypes::{DataType, Field, Schema, SchemaRef},
record_batch::RecordBatch,
};
use arrow_array::cast::AsArray;
use datafusion_common::{
internal_err, plan_err,
tree_node::{Transformed, TreeNode},
};
use datafusion_common::{plan_datafusion_err, ScalarValue};
use datafusion_physical_expr::utils::{collect_columns, Guarantee, LiteralGuarantee};
use datafusion_physical_expr::{expressions as phys_expr, PhysicalExprRef};
use log::trace;
/// Interface to pass statistics (min/max/nulls) information to [`PruningPredicate`].
///
/// Returns statistics for containers / files as Arrow [`ArrayRef`], so the
/// evaluation happens once on a single `RecordBatch`, amortizing the overhead
/// of evaluating of the predicate. This is important when pruning 1000s of
/// containers which often happens in analytic systems.
///
/// For example, for the following three files with a single column `a`:
/// ```text
/// file1: column a: min=5, max=10
/// file2: column a: No stats
/// file2: column a: min=20, max=30
/// ```
///
/// PruningStatistics would return:
///
/// ```text
/// min_values("a") -> Some([5, Null, 20])
/// max_values("a") -> Some([10, Null, 30])
/// min_values("X") -> None
/// ```
pub trait PruningStatistics {
/// Return the minimum values for the named column, if known.
///
/// If the minimum value for a particular container is not known, the
/// returned array should have `null` in that row. If the minimum value is
/// not known for any row, return `None`.
///
/// Note: the returned array must contain [`Self::num_containers`] rows
fn min_values(&self, column: &Column) -> Option<ArrayRef>;
/// Return the maximum values for the named column, if known.
///
/// See [`Self::min_values`] for when to return `None` and null values.
///
/// Note: the returned array must contain [`Self::num_containers`] rows
fn max_values(&self, column: &Column) -> Option<ArrayRef>;
/// Return the number of containers (e.g. row groups) being
/// pruned with these statistics (the number of rows in each returned array)
fn num_containers(&self) -> usize;
/// Return the number of null values for the named column as an
/// `Option<UInt64Array>`.
///
/// See [`Self::min_values`] for when to return `None` and null values.
///
/// Note: the returned array must contain [`Self::num_containers`] rows
fn null_counts(&self, column: &Column) -> Option<ArrayRef>;
/// Returns an array where each row represents information known about
/// the `values` contained in a column.
///
/// This API is designed to be used along with [`LiteralGuarantee`] to prove
/// that predicates can not possibly evaluate to `true` and thus prune
/// containers. For example, Parquet Bloom Filters can prove that values are
/// not present.
///
/// The returned array has one row for each container, with the following
/// meanings:
/// * `true` if the values in `column` ONLY contain values from `values`
/// * `false` if the values in `column` are NOT ANY of `values`
/// * `null` if the neither of the above holds or is unknown.
///
/// If these statistics can not determine column membership for any
/// container, return `None` (the default).
///
/// Note: the returned array must contain [`Self::num_containers`] rows
fn contained(
&self,
column: &Column,
values: &HashSet<ScalarValue>,
) -> Option<BooleanArray>;
}
/// Evaluates filter expressions on statistics such as min/max values and null
/// counts, attempting to prove a "container" (e.g. Parquet Row Group) can be
/// skipped without reading the actual data, potentially leading to significant
/// performance improvements.
///
/// For example, [`PruningPredicate`]s are used to prune Parquet Row Groups
/// based on the min/max values found in the Parquet metadata. If the
/// `PruningPredicate` can guarantee that no rows in the Row Group match the
/// filter, the entire Row Group is skipped during query execution.
///
/// The `PruningPredicate` API is general, allowing it to be used for pruning
/// other types of containers (e.g. files) based on statistics that may be
/// known from external catalogs (e.g. Delta Lake) or other sources. Thus it
/// supports:
///
/// 1. Arbitrary expressions expressions (including user defined functions)
///
/// 2. Vectorized evaluation (provide more than one set of statistics at a time)
/// so it is suitable for pruning 1000s of containers.
///
/// 3. Anything that implements the [`PruningStatistics`] trait, not just
/// Parquet metadata.
///
/// # Example
///
/// Given an expression like `x = 5` and statistics for 3 containers (Row
/// Groups, files, etc) `A`, `B`, and `C`:
///
/// ```text
/// A: {x_min = 0, x_max = 4}
/// B: {x_min = 2, x_max = 10}
/// C: {x_min = 5, x_max = 8}
/// ```
///
/// Applying the `PruningPredicate` will concludes that `A` can be pruned:
///
/// ```text
/// A: false (no rows could possibly match x = 5)
/// B: true (rows might match x = 5)
/// C: true (rows might match x = 5)
/// ```
///
/// See [`PruningPredicate::try_new`] and [`PruningPredicate::prune`] for more information.
#[derive(Debug, Clone)]
pub struct PruningPredicate {
/// The input schema against which the predicate will be evaluated
schema: SchemaRef,
/// A min/max pruning predicate (rewritten in terms of column min/max
/// values, which are supplied by statistics)
predicate_expr: Arc<dyn PhysicalExpr>,
/// Description of which statistics are required to evaluate `predicate_expr`
required_columns: RequiredColumns,
/// Original physical predicate from which this predicate expr is derived
/// (required for serialization)
orig_expr: Arc<dyn PhysicalExpr>,
/// [`LiteralGuarantee`]s that are used to try and prove a predicate can not
/// possibly evaluate to `true`.
literal_guarantees: Vec<LiteralGuarantee>,
}
impl PruningPredicate {
/// Try to create a new instance of [`PruningPredicate`]
///
/// This will translate the provided `expr` filter expression into
/// a *pruning predicate*.
///
/// A pruning predicate is one that has been rewritten in terms of
/// the min and max values of column references and that evaluates
/// to FALSE if the filter predicate would evaluate FALSE *for
/// every row* whose values fell within the min / max ranges (aka
/// could be pruned).
///
/// The pruning predicate evaluates to TRUE or NULL
/// if the filter predicate *might* evaluate to TRUE for at least
/// one row whose values fell within the min/max ranges (in other
/// words they might pass the predicate)
///
/// For example, the filter expression `(column / 2) = 4` becomes
/// the pruning predicate
/// `(column_min / 2) <= 4 && 4 <= (column_max / 2))`
pub fn try_new(expr: Arc<dyn PhysicalExpr>, schema: SchemaRef) -> Result<Self> {
// build predicate expression once
let mut required_columns = RequiredColumns::new();
let predicate_expr =
build_predicate_expression(&expr, schema.as_ref(), &mut required_columns);
let literal_guarantees = LiteralGuarantee::analyze(&expr);
Ok(Self {
schema,
predicate_expr,
required_columns,
orig_expr: expr,
literal_guarantees,
})
}
/// For each set of statistics, evaluates the pruning predicate
/// and returns a `bool` with the following meaning for a
/// all rows whose values match the statistics:
///
/// `true`: There MAY be rows that match the predicate
///
/// `false`: There are no rows that could possibly match the predicate
///
/// Note: the predicate passed to `prune` should already be simplified as
/// much as possible (e.g. this pass doesn't handle some
/// expressions like `b = false`, but it does handle the
/// simplified version `b`. See [`ExprSimplifier`] to simplify expressions.
///
/// [`ExprSimplifier`]: crate::optimizer::simplify_expressions::ExprSimplifier
pub fn prune<S: PruningStatistics>(&self, statistics: &S) -> Result<Vec<bool>> {
let mut builder = BoolVecBuilder::new(statistics.num_containers());
// Try to prove the predicate can't be true for the containers based on
// literal guarantees
for literal_guarantee in &self.literal_guarantees {
let LiteralGuarantee {
column,
guarantee,
literals,
} = literal_guarantee;
if let Some(results) = statistics.contained(column, literals) {
match guarantee {
// `In` means the values in the column must be one of the
// values in the set for the predicate to evaluate to true.
// If `contained` returns false, that means the column is
// not any of the values so we can prune the container
Guarantee::In => builder.combine_array(&results),
// `NotIn` means the values in the column must must not be
// any of the values in the set for the predicate to
// evaluate to true. If contained returns true, it means the
// column is only in the set of values so we can prune the
// container
Guarantee::NotIn => {
builder.combine_array(&arrow::compute::not(&results)?)
}
}
// if all containers are pruned (has rows that DEFINITELY DO NOT pass the predicate)
// can return early without evaluating the rest of predicates.
if builder.check_all_pruned() {
return Ok(builder.build());
}
}
}
// Next, try to prove the predicate can't be true for the containers based
// on min/max values
// build a RecordBatch that contains the min/max values in the
// appropriate statistics columns for the min/max predicate
let statistics_batch =
build_statistics_record_batch(statistics, &self.required_columns)?;
// Evaluate the pruning predicate on that record batch and append any results to the builder
builder.combine_value(self.predicate_expr.evaluate(&statistics_batch)?);
Ok(builder.build())
}
/// Return a reference to the input schema
pub fn schema(&self) -> &SchemaRef {
&self.schema
}
/// Returns a reference to the physical expr used to construct this pruning predicate
pub fn orig_expr(&self) -> &Arc<dyn PhysicalExpr> {
&self.orig_expr
}
/// Returns a reference to the predicate expr
pub fn predicate_expr(&self) -> &Arc<dyn PhysicalExpr> {
&self.predicate_expr
}
/// Returns true if this pruning predicate is "always true" (aka will not prune anything)
pub fn allways_true(&self) -> bool {
is_always_true(&self.predicate_expr)
}
pub(crate) fn required_columns(&self) -> &RequiredColumns {
&self.required_columns
}
/// Names of the columns that are known to be / not be in a set
/// of literals (constants). These are the columns the that may be passed to
/// [`PruningStatistics::contained`] during pruning.
///
/// This is useful to avoid fetching statistics for columns that will not be
/// used in the predicate. For example, it can be used to avoid reading
/// uneeded bloom filters (a non trivial operation).
pub fn literal_columns(&self) -> Vec<String> {
let mut seen = HashSet::new();
self.literal_guarantees
.iter()
.map(|e| &e.column.name)
// avoid duplicates
.filter(|name| seen.insert(*name))
.map(|s| s.to_string())
.collect()
}
}
/// Builds the return `Vec` for [`PruningPredicate::prune`].
#[derive(Debug)]
struct BoolVecBuilder {
/// One element per container. Each element is
/// * `true`: if the container has row that may pass the predicate
/// * `false`: if the container has rows that DEFINITELY DO NOT pass the predicate
inner: Vec<bool>,
}
impl BoolVecBuilder {
/// Create a new `BoolVecBuilder` with `num_containers` elements
fn new(num_containers: usize) -> Self {
Self {
// assume by default all containers may pass the predicate
inner: vec![true; num_containers],
}
}
/// Combines result `array` for a conjunct (e.g. `AND` clause) of a
/// predicate into the currently in progress array.
///
/// Each `array` element is:
/// * `true`: container has row that may pass the predicate
/// * `false`: all container rows DEFINITELY DO NOT pass the predicate
/// * `null`: container may or may not have rows that pass the predicate
fn combine_array(&mut self, array: &BooleanArray) {
assert_eq!(array.len(), self.inner.len());
for (cur, new) in self.inner.iter_mut().zip(array.iter()) {
// `false` for this conjunct means we know for sure no rows could
// pass the predicate and thus we set the corresponding container
// location to false.
if let Some(false) = new {
*cur = false;
}
}
}
/// Combines the results in the [`ColumnarValue`] to the currently in
/// progress array, following the same rules as [`Self::combine_array`].
///
/// # Panics
/// If `value` is not boolean
fn combine_value(&mut self, value: ColumnarValue) {
match value {
ColumnarValue::Array(array) => {
self.combine_array(array.as_boolean());
}
ColumnarValue::Scalar(ScalarValue::Boolean(Some(false))) => {
// False means all containers can not pass the predicate
self.inner = vec![false; self.inner.len()];
}
_ => {
// Null or true means the rows in container may pass this
// conjunct so we can't prune any containers based on that
}
}
}
/// Convert this builder into a Vec of bools
fn build(self) -> Vec<bool> {
self.inner
}
/// Check all containers has rows that DEFINITELY DO NOT pass the predicate
fn check_all_pruned(&self) -> bool {
self.inner.iter().all(|&x| !x)
}
}
fn is_always_true(expr: &Arc<dyn PhysicalExpr>) -> bool {
expr.as_any()
.downcast_ref::<phys_expr::Literal>()
.map(|l| matches!(l.value(), ScalarValue::Boolean(Some(true))))
.unwrap_or_default()
}
/// Describes which columns statistics are necessary to evaluate a
/// [`PruningPredicate`].
///
/// This structure permits reading and creating the minimum number statistics,
/// which is important since statistics may be non trivial to read (e.g. large
/// strings or when there are 1000s of columns).
///
/// Handles creating references to the min/max statistics
/// for columns as well as recording which statistics are needed
#[derive(Debug, Default, Clone)]
pub(crate) struct RequiredColumns {
/// The statistics required to evaluate this predicate:
/// * The unqualified column in the input schema
/// * Statistics type (e.g. Min or Max or Null_Count)
/// * The field the statistics value should be placed in for
/// pruning predicate evaluation (e.g. `min_value` or `max_value`)
columns: Vec<(phys_expr::Column, StatisticsType, Field)>,
}
impl RequiredColumns {
fn new() -> Self {
Self::default()
}
/// Returns number of unique columns
pub(crate) fn n_columns(&self) -> usize {
self.iter()
.map(|(c, _s, _f)| c)
.collect::<HashSet<_>>()
.len()
}
/// Returns an iterator over items in columns (see doc on
/// `self.columns` for details)
pub(crate) fn iter(
&self,
) -> impl Iterator<Item = &(phys_expr::Column, StatisticsType, Field)> {
self.columns.iter()
}
fn find_stat_column(
&self,
column: &phys_expr::Column,
statistics_type: StatisticsType,
) -> Option<usize> {
self.columns
.iter()
.enumerate()
.find(|(_i, (c, t, _f))| c == column && t == &statistics_type)
.map(|(i, (_c, _t, _f))| i)
}
/// Rewrites column_expr so that all appearances of column
/// are replaced with a reference to either the min or max
/// statistics column, while keeping track that a reference to the statistics
/// column is required
///
/// for example, an expression like `col("foo") > 5`, when called
/// with Max would result in an expression like `col("foo_max") >
/// 5` with the appropriate entry noted in self.columns
fn stat_column_expr(
&mut self,
column: &phys_expr::Column,
column_expr: &Arc<dyn PhysicalExpr>,
field: &Field,
stat_type: StatisticsType,
suffix: &str,
) -> Result<Arc<dyn PhysicalExpr>> {
let (idx, need_to_insert) = match self.find_stat_column(column, stat_type) {
Some(idx) => (idx, false),
None => (self.columns.len(), true),
};
let stat_column =
phys_expr::Column::new(&format!("{}_{}", column.name(), suffix), idx);
// only add statistics column if not previously added
if need_to_insert {
// may be null if statistics are not present
let nullable = true;
let stat_field =
Field::new(stat_column.name(), field.data_type().clone(), nullable);
self.columns.push((column.clone(), stat_type, stat_field));
}
rewrite_column_expr(column_expr.clone(), column, &stat_column)
}
/// rewrite col --> col_min
fn min_column_expr(
&mut self,
column: &phys_expr::Column,
column_expr: &Arc<dyn PhysicalExpr>,
field: &Field,
) -> Result<Arc<dyn PhysicalExpr>> {
self.stat_column_expr(column, column_expr, field, StatisticsType::Min, "min")
}
/// rewrite col --> col_max
fn max_column_expr(
&mut self,
column: &phys_expr::Column,
column_expr: &Arc<dyn PhysicalExpr>,
field: &Field,
) -> Result<Arc<dyn PhysicalExpr>> {
self.stat_column_expr(column, column_expr, field, StatisticsType::Max, "max")
}
/// rewrite col --> col_null_count
fn null_count_column_expr(
&mut self,
column: &phys_expr::Column,
column_expr: &Arc<dyn PhysicalExpr>,
field: &Field,
) -> Result<Arc<dyn PhysicalExpr>> {
self.stat_column_expr(
column,
column_expr,
field,
StatisticsType::NullCount,
"null_count",
)
}
}
impl From<Vec<(phys_expr::Column, StatisticsType, Field)>> for RequiredColumns {
fn from(columns: Vec<(phys_expr::Column, StatisticsType, Field)>) -> Self {
Self { columns }
}
}
/// Build a RecordBatch from a list of statistics, creating arrays,
/// with one row for each PruningStatistics and columns specified in
/// in the required_columns parameter.
///
/// For example, if the requested columns are
/// ```text
/// ("s1", Min, Field:s1_min)
/// ("s2", Max, field:s2_max)
///```
///
/// And the input statistics had
/// ```text
/// S1(Min: 5, Max: 10)
/// S2(Min: 99, Max: 1000)
/// S3(Min: 1, Max: 2)
/// ```
///
/// Then this function would build a record batch with 2 columns and
/// one row s1_min and s2_max as follows (s3 is not requested):
///
/// ```text
/// s1_min | s2_max
/// -------+--------
/// 5 | 1000
/// ```
fn build_statistics_record_batch<S: PruningStatistics>(
statistics: &S,
required_columns: &RequiredColumns,
) -> Result<RecordBatch> {
let mut fields = Vec::<Field>::new();
let mut arrays = Vec::<ArrayRef>::new();
// For each needed statistics column:
for (column, statistics_type, stat_field) in required_columns.iter() {
let column = Column::from_name(column.name());
let data_type = stat_field.data_type();
let num_containers = statistics.num_containers();
let array = match statistics_type {
StatisticsType::Min => statistics.min_values(&column),
StatisticsType::Max => statistics.max_values(&column),
StatisticsType::NullCount => statistics.null_counts(&column),
};
let array = array.unwrap_or_else(|| new_null_array(data_type, num_containers));
if num_containers != array.len() {
return internal_err!(
"mismatched statistics length. Expected {}, got {}",
num_containers,
array.len()
);
}
// cast statistics array to required data type (e.g. parquet
// provides timestamp statistics as "Int64")
let array = arrow::compute::cast(&array, data_type)?;
fields.push(stat_field.clone());
arrays.push(array);
}
let schema = Arc::new(Schema::new(fields));
// provide the count in case there were no needed statistics
let mut options = RecordBatchOptions::default();
options.row_count = Some(statistics.num_containers());
trace!(
"Creating statistics batch for {:#?} with {:#?}",
required_columns,
arrays
);
RecordBatch::try_new_with_options(schema, arrays, &options).map_err(|err| {
plan_datafusion_err!("Can not create statistics record batch: {err}")
})
}
struct PruningExpressionBuilder<'a> {
column: phys_expr::Column,
column_expr: Arc<dyn PhysicalExpr>,
op: Operator,
scalar_expr: Arc<dyn PhysicalExpr>,
field: &'a Field,
required_columns: &'a mut RequiredColumns,
}
impl<'a> PruningExpressionBuilder<'a> {
fn try_new(
left: &'a Arc<dyn PhysicalExpr>,
right: &'a Arc<dyn PhysicalExpr>,
op: Operator,
schema: &'a Schema,
required_columns: &'a mut RequiredColumns,
) -> Result<Self> {
// find column name; input could be a more complicated expression
let left_columns = collect_columns(left);
let right_columns = collect_columns(right);
let (column_expr, scalar_expr, columns, correct_operator) =
match (left_columns.len(), right_columns.len()) {
(1, 0) => (left, right, left_columns, op),
(0, 1) => (right, left, right_columns, reverse_operator(op)?),
_ => {
// if more than one column used in expression - not supported
return plan_err!(
"Multi-column expressions are not currently supported"
);
}
};
let df_schema = DFSchema::try_from(schema.clone())?;
let (column_expr, correct_operator, scalar_expr) = rewrite_expr_to_prunable(
column_expr,
correct_operator,
scalar_expr,
df_schema,
)?;
let column = columns.iter().next().unwrap().clone();
let field = match schema.column_with_name(column.name()) {
Some((_, f)) => f,
_ => {
return plan_err!("Field not found in schema");
}
};
Ok(Self {
column,
column_expr,
op: correct_operator,
scalar_expr,
field,
required_columns,
})
}
fn op(&self) -> Operator {
self.op
}
fn scalar_expr(&self) -> &Arc<dyn PhysicalExpr> {
&self.scalar_expr
}
fn min_column_expr(&mut self) -> Result<Arc<dyn PhysicalExpr>> {
self.required_columns
.min_column_expr(&self.column, &self.column_expr, self.field)
}
fn max_column_expr(&mut self) -> Result<Arc<dyn PhysicalExpr>> {
self.required_columns
.max_column_expr(&self.column, &self.column_expr, self.field)
}
}
/// This function is designed to rewrite the column_expr to
/// ensure the column_expr is monotonically increasing.
///
/// For example,
/// 1. `col > 10`
/// 2. `-col > 10` should be rewritten to `col < -10`
/// 3. `!col = true` would be rewritten to `col = !true`
/// 4. `abs(a - 10) > 0` not supported
/// 5. `cast(can_prunable_expr) > 10`
/// 6. `try_cast(can_prunable_expr) > 10`
///
/// More rewrite rules are still in progress.
fn rewrite_expr_to_prunable(
column_expr: &PhysicalExprRef,
op: Operator,
scalar_expr: &PhysicalExprRef,
schema: DFSchema,
) -> Result<(PhysicalExprRef, Operator, PhysicalExprRef)> {
if !is_compare_op(op) {
return plan_err!("rewrite_expr_to_prunable only support compare expression");
}
let column_expr_any = column_expr.as_any();
if column_expr_any
.downcast_ref::<phys_expr::Column>()
.is_some()
{
// `col op lit()`
Ok((column_expr.clone(), op, scalar_expr.clone()))
} else if let Some(cast) = column_expr_any.downcast_ref::<phys_expr::CastExpr>() {
// `cast(col) op lit()`
let arrow_schema: SchemaRef = schema.clone().into();
let from_type = cast.expr().data_type(&arrow_schema)?;
verify_support_type_for_prune(&from_type, cast.cast_type())?;
let (left, op, right) =
rewrite_expr_to_prunable(cast.expr(), op, scalar_expr, schema)?;
let left = Arc::new(phys_expr::CastExpr::new(
left,
cast.cast_type().clone(),
None,
));
Ok((left, op, right))
} else if let Some(try_cast) =
column_expr_any.downcast_ref::<phys_expr::TryCastExpr>()
{
// `try_cast(col) op lit()`
let arrow_schema: SchemaRef = schema.clone().into();
let from_type = try_cast.expr().data_type(&arrow_schema)?;
verify_support_type_for_prune(&from_type, try_cast.cast_type())?;
let (left, op, right) =
rewrite_expr_to_prunable(try_cast.expr(), op, scalar_expr, schema)?;
let left = Arc::new(phys_expr::TryCastExpr::new(
left,
try_cast.cast_type().clone(),
));
Ok((left, op, right))
} else if let Some(neg) = column_expr_any.downcast_ref::<phys_expr::NegativeExpr>() {
// `-col > lit()` --> `col < -lit()`
let (left, op, right) =
rewrite_expr_to_prunable(neg.arg(), op, scalar_expr, schema)?;
let right = Arc::new(phys_expr::NegativeExpr::new(right));
Ok((left, reverse_operator(op)?, right))
} else if let Some(not) = column_expr_any.downcast_ref::<phys_expr::NotExpr>() {
// `!col = true` --> `col = !true`
if op != Operator::Eq && op != Operator::NotEq {
return plan_err!("Not with operator other than Eq / NotEq is not supported");
}
if not
.arg()
.as_any()
.downcast_ref::<phys_expr::Column>()
.is_some()
{
let left = not.arg().clone();
let right = Arc::new(phys_expr::NotExpr::new(scalar_expr.clone()));
Ok((left, reverse_operator(op)?, right))
} else {
plan_err!("Not with complex expression {column_expr:?} is not supported")
}
} else {
plan_err!("column expression {column_expr:?} is not supported")
}
}
fn is_compare_op(op: Operator) -> bool {
matches!(
op,
Operator::Eq
| Operator::NotEq
| Operator::Lt
| Operator::LtEq
| Operator::Gt
| Operator::GtEq
)
}
// The pruning logic is based on the comparing the min/max bounds.
// Must make sure the two type has order.
// For example, casts from string to numbers is not correct.
// Because the "13" is less than "3" with UTF8 comparison order.
fn verify_support_type_for_prune(from_type: &DataType, to_type: &DataType) -> Result<()> {
// TODO: support other data type for prunable cast or try cast
if matches!(
from_type,
DataType::Int8
| DataType::Int16
| DataType::Int32
| DataType::Int64
| DataType::Decimal128(_, _)
) && matches!(
to_type,
DataType::Int8 | DataType::Int32 | DataType::Int64 | DataType::Decimal128(_, _)
) {
Ok(())
} else {
plan_err!(
"Try Cast/Cast with from type {from_type} to type {to_type} is not supported"
)
}
}
/// replaces a column with an old name with a new name in an expression
fn rewrite_column_expr(
e: Arc<dyn PhysicalExpr>,
column_old: &phys_expr::Column,
column_new: &phys_expr::Column,
) -> Result<Arc<dyn PhysicalExpr>> {
e.transform(&|expr| {
if let Some(column) = expr.as_any().downcast_ref::<phys_expr::Column>() {
if column == column_old {
return Ok(Transformed::Yes(Arc::new(column_new.clone())));
}
}
Ok(Transformed::No(expr))
})
}
fn reverse_operator(op: Operator) -> Result<Operator> {
op.swap().ok_or_else(|| {
DataFusionError::Internal(format!(
"Could not reverse operator {op} while building pruning predicate"
))
})
}
/// Given a column reference to `column`, returns a pruning
/// expression in terms of the min and max that will evaluate to true
/// if the column may contain values, and false if definitely does not
/// contain values
fn build_single_column_expr(
column: &phys_expr::Column,
schema: &Schema,
required_columns: &mut RequiredColumns,
is_not: bool, // if true, treat as !col
) -> Option<Arc<dyn PhysicalExpr>> {
let field = schema.field_with_name(column.name()).ok()?;
if matches!(field.data_type(), &DataType::Boolean) {
let col_ref = Arc::new(column.clone()) as _;
let min = required_columns
.min_column_expr(column, &col_ref, field)
.ok()?;
let max = required_columns
.max_column_expr(column, &col_ref, field)
.ok()?;
// remember -- we want an expression that is:
// TRUE: if there may be rows that match
// FALSE: if there are no rows that match
if is_not {
// The only way we know a column couldn't match is if both the min and max are true
// !(min && max)
Some(Arc::new(phys_expr::NotExpr::new(Arc::new(
phys_expr::BinaryExpr::new(min, Operator::And, max),
))))
} else {
// the only way we know a column couldn't match is if both the min and max are false
// !(!min && !max) --> min || max
Some(Arc::new(phys_expr::BinaryExpr::new(min, Operator::Or, max)))
}
} else {
None
}
}
/// Given an expression reference to `expr`, if `expr` is a column expression,
/// returns a pruning expression in terms of IsNull that will evaluate to true
/// if the column may contain null, and false if definitely does not
/// contain null.
fn build_is_null_column_expr(
expr: &Arc<dyn PhysicalExpr>,
schema: &Schema,
required_columns: &mut RequiredColumns,
) -> Option<Arc<dyn PhysicalExpr>> {
if let Some(col) = expr.as_any().downcast_ref::<phys_expr::Column>() {
let field = schema.field_with_name(col.name()).ok()?;
let null_count_field = &Field::new(field.name(), DataType::UInt64, true);
required_columns
.null_count_column_expr(col, expr, null_count_field)
.map(|null_count_column_expr| {
// IsNull(column) => null_count > 0
Arc::new(phys_expr::BinaryExpr::new(
null_count_column_expr,
Operator::Gt,
Arc::new(phys_expr::Literal::new(ScalarValue::UInt64(Some(0)))),
)) as _
})
.ok()
} else {
None
}
}
/// Translate logical filter expression into pruning predicate
/// expression that will evaluate to FALSE if it can be determined no
/// rows between the min/max values could pass the predicates.
///
/// Returns the pruning predicate as an [`PhysicalExpr`]
fn build_predicate_expression(
expr: &Arc<dyn PhysicalExpr>,
schema: &Schema,
required_columns: &mut RequiredColumns,
) -> Arc<dyn PhysicalExpr> {
// Returned for unsupported expressions. Such expressions are
// converted to TRUE.
let unhandled = Arc::new(phys_expr::Literal::new(ScalarValue::Boolean(Some(true))));
// predicate expression can only be a binary expression
let expr_any = expr.as_any();
if let Some(is_null) = expr_any.downcast_ref::<phys_expr::IsNullExpr>() {
return build_is_null_column_expr(is_null.arg(), schema, required_columns)
.unwrap_or(unhandled);
}
if let Some(col) = expr_any.downcast_ref::<phys_expr::Column>() {
return build_single_column_expr(col, schema, required_columns, false)
.unwrap_or(unhandled);
}
if let Some(not) = expr_any.downcast_ref::<phys_expr::NotExpr>() {
// match !col (don't do so recursively)
if let Some(col) = not.arg().as_any().downcast_ref::<phys_expr::Column>() {
return build_single_column_expr(col, schema, required_columns, true)
.unwrap_or(unhandled);
} else {
return unhandled;
}
}
if let Some(in_list) = expr_any.downcast_ref::<phys_expr::InListExpr>() {
if !in_list.list().is_empty() && in_list.list().len() < 20 {
let eq_op = if in_list.negated() {
Operator::NotEq
} else {
Operator::Eq
};
let re_op = if in_list.negated() {
Operator::And
} else {
Operator::Or
};
let change_expr = in_list
.list()
.iter()
.cloned()
.map(|e| {
Arc::new(phys_expr::BinaryExpr::new(
in_list.expr().clone(),
eq_op,
e.clone(),
)) as _
})
.reduce(|a, b| Arc::new(phys_expr::BinaryExpr::new(a, re_op, b)) as _)
.unwrap();
return build_predicate_expression(&change_expr, schema, required_columns);
} else {
return unhandled;
}
}
let (left, op, right) = {
if let Some(bin_expr) = expr_any.downcast_ref::<phys_expr::BinaryExpr>() {
(
bin_expr.left().clone(),
*bin_expr.op(),
bin_expr.right().clone(),
)
} else {
return unhandled;
}
};
if op == Operator::And || op == Operator::Or {
let left_expr = build_predicate_expression(&left, schema, required_columns);
let right_expr = build_predicate_expression(&right, schema, required_columns);
// simplify boolean expression if applicable
let expr = match (&left_expr, op, &right_expr) {
(left, Operator::And, _) if is_always_true(left) => right_expr,
(_, Operator::And, right) if is_always_true(right) => left_expr,
(left, Operator::Or, right)
if is_always_true(left) || is_always_true(right) =>
{
unhandled
}
_ => Arc::new(phys_expr::BinaryExpr::new(left_expr, op, right_expr)),
};
return expr;
}
let expr_builder =
PruningExpressionBuilder::try_new(&left, &right, op, schema, required_columns);
let mut expr_builder = match expr_builder {
Ok(builder) => builder,
// allow partial failure in predicate expression generation
// this can still produce a useful predicate when multiple conditions are joined using AND