Better Reserve() on index column of LC

Enmk · web-flow · commit b7f654cbf6f3 · 2025-06-06T18:14:18.000+02:00
diff --git a/clickhouse/columns/lowcardinality.cpp b/clickhouse/columns/lowcardinality.cpp
@@ -180,7 +180,7 @@ void ColumnLowCardinality::Reserve(size_t new_cap) {
     // NOTE(vnemkov): Formula below (`ceil(sqrt(x))`) is a gut-feeling-good-enough estimation,
     // feel free to replace/adjust if you have better one suported by actual data.
     dictionary_column_->Reserve(static_cast<size_t>(ceil(sqrt(new_cap))));
-    index_column_->Reserve(new_cap);
+    index_column_->Reserve(new_cap + 2); // + 1 for null item (at pos 0), + 1 for default item (at pos 1)
 }
 
 void ColumnLowCardinality::Setup(ColumnRef dictionary_column) {

Original file line number	Diff line number	Diff line change
`@@ -180,7 +180,7 @@ void ColumnLowCardinality::Reserve(size_t new_cap) {`
`180`	`180`	// NOTE(vnemkov): Formula below (`ceil(sqrt(x))`) is a gut-feeling-good-enough estimation,
`181`	`181`	`// feel free to replace/adjust if you have better one suported by actual data.`
`182`	`182`	`dictionary_column_->Reserve(static_cast<size_t>(ceil(sqrt(new_cap))));`
`183`		`- index_column_->Reserve(new_cap);`
	`183`	`+ index_column_->Reserve(new_cap + 2); // + 1 for null item (at pos 0), + 1 for default item (at pos 1)`
`184`	`184`	`}`
`185`	`185`
`186`	`186`	`void ColumnLowCardinality::Setup(ColumnRef dictionary_column) {`