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Add comment about double-close in ColumnSelectorColumnIndexSelector. (#12735)

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Gian Merlino 2022-07-06 00:50:35 -07:00 committed by GitHub
parent 682ea7f32d
commit 49feffff1b
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1 changed files with 12 additions and 1 deletions
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13
processing/src/main/java/org/apache/druid/segment/ColumnSelectorColumnIndexSelector.java
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@ -29,6 +29,7 @@ import org.apache.druid.segment.column.NumericColumn;
import javax.annotation.Nullable;
/**
*
*/
public class ColumnSelectorColumnIndexSelector implements ColumnIndexSelector
{
@ -50,7 +51,17 @@ public class ColumnSelectorColumnIndexSelector implements ColumnIndexSelector
@Override
public int getNumRows()
{
try (final NumericColumn column = (NumericColumn) columnSelector.getColumnHolder(ColumnHolder.TIME_COLUMN_NAME).getColumn()) {
// This closes the __time column, which may initially seem like good behavior, but in reality leads to a
// double-close when columnSelector is a ColumnCache (because all columns from a ColumnCache are closed when
// the cache itself is closed). We're closing it here anyway, however, for two reasons:
//
// 1) Sometimes, columnSelector is DeprecatedQueryableIndexColumnSelector, not ColumnCache, and so the close
// here is important.
// 2) Double-close is OK for the __time column when this method is expected to be used: the __time column is
// expected to be a ColumnarLongs, which is safe to double-close.
try (final NumericColumn column = (NumericColumn) columnSelector.getColumnHolder(ColumnHolder.TIME_COLUMN_NAME)
.getColumn()) {
return column.length();
}
}