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Cleanup and improve emitter.rs docs

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jussisaurio
2024-08-17 13:56:59 +03:00
parent e8c894e532
commit d7d195a618
1 changed files with 38 additions and 13 deletions
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51
core/translate/emitter.rs
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@@ -60,23 +60,50 @@ pub struct LeftJoinMetadata {
#[derive(Debug)]
pub struct SortMetadata {
// cursor id for the Sorter table where the sorted rows are stored
pub sort_cursor: usize,
// cursor id for the Pseudo table where rows are temporarily inserted from the Sorter table
pub pseudo_table_cursor: usize,
pub sort_register: usize,
pub next_row_label: BranchOffset,
// label where the SorterData instruction is emitted; SorterNext will jump here if there is more data to read
pub sorter_data_label: BranchOffset,
// label for the instruction immediately following SorterNext; SorterSort will jump here in case there is no data
pub done_label: BranchOffset,
}
#[derive(Debug)]
pub struct Metadata {
// labels for the instructions that terminate the execution when a conditional check evaluates to false. typically jumps to Halt, but can also jump to AggFinal if a parent in the tree is an aggregation
termination_labels: Vec<BranchOffset>,
// labels for the instructions that jump to the next row in the current operator.
// for example, in a join with two nested scans, the inner loop will jump to its Next instruction when the join condition is false;
// in a join with a scan and a seek, the seek will jump to the scan's Next instruction when the join condition is false.
next_row_labels: HashMap<usize, BranchOffset>,
// labels for the Rewind instructions.
rewind_labels: Vec<BranchOffset>,
aggregations: HashMap<usize, usize>,
// mapping between Aggregation operator id and the register that holds the start of the aggregation result
aggregation_start_registers: HashMap<usize, usize>,
// mapping between Order operator id and associated metadata
sorts: HashMap<usize, SortMetadata>,
// mapping between Join operator id and associated metadata (for left joins only)
left_joins: HashMap<usize, LeftJoinMetadata>,
}
/**
* Emitters return one of three possible results from the step() method:
* - Continue: the operator is not yet ready to emit a result row
* - ReadyToEmit: the operator is ready to emit a result row
* - Done: the operator has completed execution
* For example, a Scan operator will return Continue until it has opened a cursor, rewound it and applied any predicates.
* At that point, it will return ReadyToEmit.
* Finally, when the Scan operator has emitted a Next instruction, it will return Done.
*
* Parent operators are free to make decisions based on the result a child operator's step() method.
*
* When the root operator of a Plan returns ReadyToEmit, a ResultRow will always be emitted.
* When the root operator returns Done, the bytecode plan is complete.
*
*/
#[derive(Debug, PartialEq)]
pub enum OpStepResult {
Continue,
@@ -392,7 +419,7 @@ impl Emitter for Operator {
m.termination_labels.push(agg_final_label);
let num_aggs = aggregates.len();
let start_reg = program.alloc_registers(num_aggs);
m.aggregations.insert(*id, start_reg);
m.aggregation_start_registers.insert(*id, start_reg);
Ok(OpStepResult::Continue)
}
@@ -400,7 +427,7 @@ impl Emitter for Operator {
match source.step(program, m, referenced_tables)? {
OpStepResult::Continue => {}
OpStepResult::ReadyToEmit => {
let start_reg = m.aggregations.get(id).unwrap();
let start_reg = m.aggregation_start_registers.get(id).unwrap();
for (i, agg) in aggregates.iter().enumerate() {
let agg_result_reg = start_reg + i;
translate_aggregation(
@@ -452,8 +479,7 @@ impl Emitter for Operator {
SortMetadata {
sort_cursor,
pseudo_table_cursor: usize::MAX, // will be set later
sort_register: usize::MAX, // will be set later
next_row_label: program.allocate_label(),
sorter_data_label: program.allocate_label(),
done_label: program.allocate_label(),
},
);
@@ -501,7 +527,6 @@ impl Emitter for Operator {
cursor_id: sort_metadata.sort_cursor,
record_reg: dest,
});
sort_metadata.sort_register = start_reg;
Ok(OpStepResult::Continue)
}
@@ -548,7 +573,7 @@ impl Emitter for Operator {
);
program.defer_label_resolution(
sort_metadata.next_row_label,
sort_metadata.sorter_data_label,
program.offset() as usize,
);
program.emit_insn(Insn::SorterData {
@@ -568,9 +593,9 @@ impl Emitter for Operator {
program.emit_insn_with_label_dependency(
Insn::SorterNext {
cursor_id: sort_metadata.sort_cursor,
pc_if_next: sort_metadata.next_row_label,
pc_if_next: sort_metadata.sorter_data_label,
},
sort_metadata.next_row_label,
sort_metadata.sorter_data_label,
);
program.resolve_label(sort_metadata.done_label, program.offset());
@@ -634,7 +659,7 @@ impl Emitter for Operator {
Ok(left_start_reg)
}
Operator::Aggregate { id, aggregates, .. } => {
let start_reg = m.aggregations.get(id).unwrap();
let start_reg = m.aggregation_start_registers.get(id).unwrap();
for (i, agg) in aggregates.iter().enumerate() {
let agg_result_reg = *start_reg + i;
program.emit_insn(Insn::AggFinal {
@@ -801,7 +826,7 @@ pub fn emit_program(
termination_labels: vec![halt_label],
next_row_labels: HashMap::new(),
rewind_labels: Vec::new(),
aggregations: HashMap::new(),
aggregation_start_registers: HashMap::new(),
sorts: HashMap::new(),
left_joins: HashMap::new(),
};