dbx_core/sql/optimizer/
projection_pushdown.rs

1//! Rule 2: Projection Pushdown
2//!
3//! 불필요한 컬럼을 조기 제거하여 메모리 절감
4
5use crate::error::DbxResult;
6use crate::sql::planner::{Expr, LogicalPlan};
7
8use super::OptimizationRule;
9
10/// 불필요한 컬럼을 조기 제거하여 메모리 절감
11pub struct ProjectionPushdownRule;
12
13impl OptimizationRule for ProjectionPushdownRule {
14    fn name(&self) -> &str {
15        "ProjectionPushdown"
16    }
17
18    fn apply(&self, plan: LogicalPlan) -> DbxResult<LogicalPlan> {
19        self.push_down(plan)
20    }
21}
22
23impl ProjectionPushdownRule {
24    fn push_down(&self, plan: LogicalPlan) -> DbxResult<LogicalPlan> {
25        match plan {
26            LogicalPlan::Project {
27                input,
28                projections: columns,
29            } => {
30                let optimized_input = self.push_down(*input)?;
31                match optimized_input {
32                    LogicalPlan::Scan {
33                        table,
34                        columns: scan_cols,
35                        filter,
36                    } if !columns.is_empty() => {
37                        let needed = self.extract_column_names(&columns);
38                        let final_cols = if scan_cols.is_empty() {
39                            needed
40                        } else {
41                            scan_cols
42                                .into_iter()
43                                .filter(|c| needed.contains(c))
44                                .collect()
45                        };
46                        Ok(LogicalPlan::Project {
47                            input: Box::new(LogicalPlan::Scan {
48                                table,
49                                columns: final_cols,
50                                filter,
51                            }),
52                            projections: columns,
53                        })
54                    }
55                    other => Ok(LogicalPlan::Project {
56                        input: Box::new(other),
57                        projections: columns,
58                    }),
59                }
60            }
61            LogicalPlan::Filter { input, predicate } => Ok(LogicalPlan::Filter {
62                input: Box::new(self.push_down(*input)?),
63                predicate,
64            }),
65            LogicalPlan::Sort { input, order_by } => Ok(LogicalPlan::Sort {
66                input: Box::new(self.push_down(*input)?),
67                order_by,
68            }),
69            LogicalPlan::Limit {
70                input,
71                count,
72                offset,
73            } => Ok(LogicalPlan::Limit {
74                input: Box::new(self.push_down(*input)?),
75                count,
76                offset,
77            }),
78            LogicalPlan::Aggregate {
79                input,
80                group_by,
81                aggregates,
82            } => Ok(LogicalPlan::Aggregate {
83                input: Box::new(self.push_down(*input)?),
84                group_by,
85                aggregates,
86            }),
87            other => Ok(other),
88        }
89    }
90
91    /// Extract column names referenced in expressions.
92    fn extract_column_names(&self, projections: &[(Expr, Option<String>)]) -> Vec<String> {
93        let mut names = Vec::new();
94        for (expr, _) in projections {
95            self.collect_columns(expr, &mut names);
96        }
97        names.sort();
98        names.dedup();
99        names
100    }
101
102    fn collect_columns(&self, expr: &Expr, out: &mut Vec<String>) {
103        match expr {
104            Expr::Column(name) => out.push(name.clone()),
105            Expr::BinaryOp { left, right, .. } => {
106                self.collect_columns(left, out);
107                self.collect_columns(right, out);
108            }
109            Expr::Function { args, .. } => {
110                for arg in args {
111                    self.collect_columns(arg, out);
112                }
113            }
114            Expr::IsNull(inner) | Expr::IsNotNull(inner) => {
115                self.collect_columns(inner, out);
116            }
117            Expr::InList { expr, list, .. } => {
118                self.collect_columns(expr, out);
119                for item in list {
120                    self.collect_columns(item, out);
121                }
122            }
123            _ => {}
124        }
125    }
126}
dbx_core/sql/optimizer/projection_pushdown.rs

dbx_core/sql/optimizer/
projection_pushdown.rs
