explain.rs

// Copyright 2024 RisingLight Project Authors. Licensed under Apache-2.0.

use futures::{future, stream};
use pretty_xmlish::PrettyConfig;

use super::*;
use crate::array::{ArrayImpl, StringArray};
use crate::planner::{Explain, Optimizer};

/// The executor of `explain` statement.
pub struct ExplainExecutor {
    pub plan: RecExpr,
    pub optimizer: Optimizer,
}

impl ExplainExecutor {
    pub fn execute(self) -> BoxedExecutor {
        let costs = self.optimizer.costs(&self.plan);
        let rows = self.optimizer.rows(&self.plan);
        let get_metadata = |id| {
            vec![
                ("cost", costs[usize::from(id)].to_string()),
                ("rows", rows[usize::from(id)].to_string()),
            ]
        };
        let explain_obj = Explain::of(&self.plan)
            .with_catalog(self.optimizer.catalog())
            .with_metadata(&get_metadata);
        let explainer = explain_obj.pretty();
        let mut explain = String::with_capacity(4096);
        let mut config = PrettyConfig {
            need_boundaries: false,
            ..PrettyConfig::default()
        };
        config.unicode(&mut explain, &explainer);
        let chunk = DataChunk::from_iter([ArrayImpl::new_string(StringArray::from_iter([Some(
            explain,
        )]))]);

        stream::once(future::ok(chunk)).boxed()
    }
}