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https://issues.apache.org/jira/browse/DRILL-5796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16545044#comment-16545044
]
ASF GitHub Bot commented on DRILL-5796:
---------------------------------------
arina-ielchiieva commented on a change in pull request #1298: DRILL-5796:
Filter pruning for multi rowgroup parquet file
URL: https://github.com/apache/drill/pull/1298#discussion_r202638120
##########
File path:
exec/java-exec/src/main/java/org/apache/drill/exec/expr/stat/ParquetIsPredicate.java
##########
@@ -62,50 +62,51 @@ private ParquetIsPredicate(LogicalExpression expr,
BiPredicate<Statistics<C>, Ra
return visitor.visitUnknown(this, value);
}
- @Override
- public boolean canDrop(RangeExprEvaluator<C> evaluator) {
+ /**
+ * Apply the filter condition against the meta of the rowgroup.
+ */
+ public RowsMatch matches(RangeExprEvaluator<C> evaluator) {
Statistics<C> exprStat = expr.accept(evaluator, null);
- if (isNullOrEmpty(exprStat)) {
- return false;
- }
+ return isNullOrEmpty(exprStat) ? RowsMatch.SOME :
predicate.apply(exprStat, evaluator);
+ }
- return predicate.test(exprStat, evaluator);
+ /**
+ * After the applying of the filter against the statistics of the rowgroup,
if the result is RowsMatch.ALL,
+ * then we still must know if the rowgroup contains some null values,
because it can change the filter result.
+ * If it contains some null values, then we change the RowsMatch.ALL into
RowsMatch.SOME, which sya that maybe
+ * some values (the null ones) should be disgarded.
+ */
+ private static RowsMatch checkNull(Statistics exprStat) {
+ return hasNoNulls(exprStat) ? RowsMatch.ALL : RowsMatch.SOME;
}
/**
* IS NULL predicate.
*/
private static <C extends Comparable<C>> LogicalExpression
createIsNullPredicate(LogicalExpression expr) {
return new ParquetIsPredicate<C>(expr,
- //if there are no nulls -> canDrop
- (exprStat, evaluator) -> hasNoNulls(exprStat)) {
- private final boolean isArray = isArray(expr);
-
- private boolean isArray(LogicalExpression expression) {
- if (expression instanceof TypedFieldExpr) {
- TypedFieldExpr typedFieldExpr = (TypedFieldExpr) expression;
- SchemaPath schemaPath = typedFieldExpr.getPath();
- return schemaPath.isArray();
- }
- return false;
- }
-
- @Override
- public boolean canDrop(RangeExprEvaluator<C> evaluator) {
+ (exprStat, evaluator) -> {
// for arrays we are not able to define exact number of nulls
// [1,2,3] vs [1,2] -> in second case 3 is absent and thus it's null
but statistics shows no nulls
- return !isArray && super.canDrop(evaluator);
- }
- };
+ if (expr instanceof TypedFieldExpr) {
+ TypedFieldExpr typedFieldExpr = (TypedFieldExpr) expr;
+ if (typedFieldExpr.getPath().isArray()) {
+ return RowsMatch.SOME;
+ }
+ }
+ if (hasNoNulls(exprStat)) {
Review comment:
@jbimbert, @vrozov
https://issues.apache.org/jira/browse/DRILL-6603 use case shows that
statistics can be defined in the following way:
`stat.isEmpty()` returns `false`
`stat.getNumNulls()` returns `0`
`stat.genericGetMin()` returns `null`
`stat.genericGetMax()` returns `null`
`stat.toString` returns `num_nulls: 0, min/max not defined`
In this case we mistakenly decide that such row group does not contain null
values and filter out such rows group but in reality, row group contains nulls.
Statistics `toString` method is defined as follows:
```
@Override
public String toString() {
if (this.hasNonNullValue()) {
if (isNumNullsSet()) {
return String.format("min: %s, max: %s, num_nulls: %d",
minAsString(), maxAsString(), this.getNumNulls());
} else {
return String.format("min: %s, max: %s, num_nulls not defined",
minAsString(), maxAsString());
}
} else if (!this.isEmpty())
return String.format("num_nulls: %d, min/max not defined",
this.getNumNulls());
else
return "no stats for this column";
}
```
As you can see `toString` method also uses `stat.hasNonNullValue()` to show
if stat is defined.
In order to correctly apply `is null` we need use `stat.hasNonNullValue()`.
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> Filter pruning for multi rowgroup parquet file
> ----------------------------------------------
>
> Key: DRILL-5796
> URL: https://issues.apache.org/jira/browse/DRILL-5796
> Project: Apache Drill
> Issue Type: Improvement
> Components: Storage - Parquet
> Reporter: Damien Profeta
> Assignee: Kunal Khatua
> Priority: Major
> Fix For: 1.14.0
>
>
> Today, filter pruning use the file name as the partitioning key. This means
> you can remove a partition only if the whole file is for the same partition.
> With parquet, you can prune the filter if the rowgroup make a partition of
> your dataset as the unit of work if the rowgroup not the file.
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