hqx871 commented on a change in pull request #2363:
URL: https://github.com/apache/calcite/pull/2363#discussion_r591302751
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File path: core/src/main/java/org/apache/calcite/rel/core/Sort.java
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@@ -124,11 +125,19 @@ public abstract Sort copy(RelTraitSet traitSet, RelNode
newInput,
@Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
RelMetadataQuery mq) {
+ double rowCount = mq.getRowCount(this);
+ if (collation.getFieldCollations().isEmpty()) {
+ return planner.getCostFactory().makeCost(rowCount, 0, 0);
+ }
+ final int offsetValue = offset == null ? 0 : RexLiteral.intValue(offset);
+ final double inCount = mq.getRowCount(input);
// Higher cost if rows are wider discourages pushing a project through a
// sort.
- final double rowCount = mq.getRowCount(this);
final double bytesPerRow = getRowType().getFieldCount() * 4;
- final double cpu = Util.nLogN(rowCount) * bytesPerRow;
+ // When output count + offset is smaller than input count, we can use heap
sort,
+ // otherwise, we can use heap sort, quick sort and so on
+ final double heapSize = Math.min(rowCount + offsetValue, inCount);
Review comment:
I make a simple query and found the LogicalSort will be implemented to
EnumerableLimit and EnumerableSort. The offset and fetch will be both null, so
the sort cost is still nLogN.
Query:
select * from foodmart.sales_fact_1997 order by cust_id limit 10
Plan:
EnumerableLimit(fetch=[10]): rowcount = 10.0, cumulative cost = {210.0 rows,
3795.1361487904733 cpu, 0.0 io}, id = 35
EnumerableSort(sort0=[$0], dir0=[ASC]): rowcount = 100.0, cumulative cost
= {200.0 rows, 3785.1361487904733 cpu, 0.0 io}, id = 34
EnumerableTableScan(table=[[foodmart, sales_fact_1997]]): rowcount =
100.0, cumulative cost = {100.0 rows, 101.0 cpu, 0.0 io}, id = 20
I also checked the EnumerableSort code, as follow:
public EnumerableSort(RelOptCluster cluster, RelTraitSet traitSet,
RelNode input, RelCollation collation, @Nullable RexNode offset,
@Nullable RexNode fetch) {
super(cluster, traitSet, input, collation, offset, fetch);
assert getConvention() instanceof EnumerableConvention;
assert getConvention() == input.getConvention();
assert fetch == null : "fetch must be null";
assert offset == null : "offset must be null";
}
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