polars-plan 0.26.1

use polars_core::datatypes::PlHashMap;
use polars_core::prelude::*;

use crate::prelude::*;

mod cache_states;
#[cfg(feature = "cse")]
mod cse;
mod delay_rechunk;
mod drop_nulls;
mod fast_projection;
#[cfg(any(
    feature = "ipc",
    feature = "parquet",
    feature = "csv-file",
    feature = "cse"
))]
pub(crate) mod file_caching;
mod predicate_pushdown;
mod projection_pushdown;
mod simplify_expr;
mod slice_pushdown_expr;
mod slice_pushdown_lp;
mod stack_opt;
mod type_coercion;

use delay_rechunk::DelayRechunk;
use drop_nulls::ReplaceDropNulls;
use fast_projection::FastProjectionAndCollapse;
#[cfg(any(feature = "ipc", feature = "parquet", feature = "csv-file"))]
use file_caching::{find_column_union_and_fingerprints, FileCacher};
pub use predicate_pushdown::PredicatePushDown;
pub use projection_pushdown::ProjectionPushDown;
pub use simplify_expr::{SimplifyBooleanRule, SimplifyExprRule};
use slice_pushdown_lp::SlicePushDown;
pub use stack_opt::{OptimizationRule, StackOptimizer};
pub use type_coercion::TypeCoercionRule;

pub use crate::frame::{AllowedOptimizations, OptState};

pub trait Optimize {
    fn optimize(&self, logical_plan: LogicalPlan) -> PolarsResult<LogicalPlan>;
}

// arbitrary constant to reduce reallocation.
const HASHMAP_SIZE: usize = 16;

pub(crate) fn init_hashmap<K, V>(max_len: Option<usize>) -> PlHashMap<K, V> {
    PlHashMap::with_capacity(std::cmp::min(max_len.unwrap_or(HASHMAP_SIZE), HASHMAP_SIZE))
}

pub fn optimize(
    logical_plan: LogicalPlan,
    opt_state: OptState,
    lp_arena: &mut Arena<ALogicalPlan>,
    expr_arena: &mut Arena<AExpr>,
    scratch: &mut Vec<Node>,
) -> PolarsResult<Node> {
    // get toggle values
    let predicate_pushdown = opt_state.predicate_pushdown;
    let projection_pushdown = opt_state.projection_pushdown;
    let type_coercion = opt_state.type_coercion;
    let simplify_expr = opt_state.simplify_expr;
    let slice_pushdown = opt_state.slice_pushdown;
    let streaming = opt_state.streaming;
    #[cfg(feature = "cse")]
    let cse = opt_state.common_subplan_elimination;

    let agg_scan_projection = opt_state.file_caching;

    // gradually fill the rules passed to the optimizer
    let opt = StackOptimizer {};
    let mut rules: Vec<Box<dyn OptimizationRule>> = Vec::with_capacity(8);

    // during debug we check if the optimizations have not modified the final schema
    #[cfg(debug_assertions)]
    let prev_schema = logical_plan.schema()?.into_owned();

    let mut lp_top = to_alp(logical_plan, expr_arena, lp_arena)?;

    #[cfg(feature = "cse")]
    let cse_changed = if cse {
        let (lp, changed) = cse::elim_cmn_subplans(lp_top, lp_arena, expr_arena);
        lp_top = lp;
        changed
    } else {
        false
    };
    #[cfg(not(feature = "cse"))]
    let cse_changed = false;

    // we do simplification
    if simplify_expr {
        rules.push(Box::new(SimplifyExprRule {}));
    }

    // should be run before predicate pushdown
    if projection_pushdown {
        let projection_pushdown_opt = ProjectionPushDown {};
        let alp = lp_arena.take(lp_top);
        let alp = projection_pushdown_opt.optimize(alp, lp_arena, expr_arena)?;
        lp_arena.replace(lp_top, alp);
        cache_states::set_cache_states(lp_top, lp_arena, expr_arena, scratch, cse_changed);
    }

    if predicate_pushdown {
        let predicate_pushdown_opt = PredicatePushDown::default();
        let alp = lp_arena.take(lp_top);
        let alp = predicate_pushdown_opt.optimize(alp, lp_arena, expr_arena)?;
        lp_arena.replace(lp_top, alp);
    }

    // make sure its before slice pushdown.
    if projection_pushdown {
        rules.push(Box::new(FastProjectionAndCollapse {}));
    }
    rules.push(Box::new(DelayRechunk::new()));

    if slice_pushdown {
        let slice_pushdown_opt = SlicePushDown::new(streaming);
        let alp = lp_arena.take(lp_top);
        let alp = slice_pushdown_opt.optimize(alp, lp_arena, expr_arena)?;

        lp_arena.replace(lp_top, alp);

        // expressions use the stack optimizer
        rules.push(Box::new(slice_pushdown_opt));
    }
    if type_coercion {
        rules.push(Box::new(TypeCoercionRule {}))
    }
    // this optimization removes branches, so we must do it when type coercion
    // is completed
    if simplify_expr {
        rules.push(Box::new(SimplifyBooleanRule {}));
    }

    // make sure that we do that once slice pushdown
    // and predicate pushdown are done. At that moment
    // the file fingerprints are finished.
    #[cfg(any(
        feature = "cse",
        feature = "parquet",
        feature = "ipc",
        feature = "csv-file"
    ))]
    if agg_scan_projection || cse_changed {
        // we do this so that expressions are simplified created by the pushdown optimizations
        // we must clean up the predicates, because the agg_scan_projection
        // uses them in the hashtable to determine duplicates.
        let simplify_bools = &mut [Box::new(SimplifyBooleanRule {}) as Box<dyn OptimizationRule>];
        lp_top = opt.optimize_loop(simplify_bools, expr_arena, lp_arena, lp_top);

        // scan the LP to aggregate all the column used in scans
        // these columns will be added to the state of the AggScanProjection rule
        let mut file_predicate_to_columns_and_count = PlHashMap::with_capacity(32);
        find_column_union_and_fingerprints(
            lp_top,
            &mut file_predicate_to_columns_and_count,
            lp_arena,
            expr_arena,
        );

        let mut file_cacher = FileCacher::new(file_predicate_to_columns_and_count);
        file_cacher.assign_unions(lp_top, lp_arena, expr_arena, scratch);

        #[cfg(feature = "cse")]
        if cse_changed {
            // this must run after cse
            cse::decrement_file_counters_by_cache_hits(lp_top, lp_arena, expr_arena, 0, scratch);
        }
    }

    rules.push(Box::new(ReplaceDropNulls {}));

    lp_top = opt.optimize_loop(&mut rules, expr_arena, lp_arena, lp_top);

    // during debug we check if the optimizations have not modified the final schema
    #[cfg(debug_assertions)]
    {
        // only check by names because we may supercast types.
        assert_eq!(
            prev_schema.iter_names().collect::<Vec<_>>(),
            lp_arena
                .get(lp_top)
                .schema(lp_arena)
                .iter_names()
                .collect::<Vec<_>>()
        );
    };

    Ok(lp_top)
}

#[cfg(test)]
fn optimize_lp(lp: LogicalPlan, rules: &mut [Box<dyn OptimizationRule>]) -> LogicalPlan {
    // initialize arena's
    let mut expr_arena = Arena::with_capacity(64);
    let mut lp_arena = Arena::with_capacity(32);
    let root = to_alp(lp, &mut expr_arena, &mut lp_arena).unwrap();

    let opt = StackOptimizer {};
    let lp_top = opt.optimize_loop(rules, &mut expr_arena, &mut lp_arena, root);
    node_to_lp(lp_top, &mut expr_arena, &mut lp_arena)
}

#[cfg(test)]
fn optimize_expr(expr: Expr, schema: Schema, rules: &mut [Box<dyn OptimizationRule>]) -> Expr {
    // initialize arena's
    let mut expr_arena = Arena::with_capacity(64);
    let mut lp_arena = Arena::with_capacity(32);
    let schema = Arc::new(schema);

    // dummy input needed to put the schema
    let input = Box::new(LogicalPlan::Projection {
        expr: vec![],
        input: Box::new(Default::default()),
        schema: schema.clone(),
    });

    let lp = LogicalPlan::Projection {
        expr: vec![expr],
        input,
        schema,
    };

    let root = to_alp(lp, &mut expr_arena, &mut lp_arena).unwrap();

    let opt = StackOptimizer {};
    let lp_top = opt.optimize_loop(rules, &mut expr_arena, &mut lp_arena, root);
    if let LogicalPlan::Projection { mut expr, .. } =
        node_to_lp(lp_top, &mut expr_arena, &mut lp_arena)
    {
        expr.pop().unwrap()
    } else {
        unreachable!()
    }
}