gszadovszky commented on code in PR #1023:
URL: https://github.com/apache/parquet-mr/pull/1023#discussion_r1113333478
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parquet-hadoop/src/main/java/org/apache/parquet/filter2/statisticslevel/StatisticsFilter.java:
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@@ -289,8 +320,14 @@ public <T extends Comparable<T>> Boolean visit(Lt<T> lt) {
T value = lt.getValue();
- // drop if value <= min
- return stats.compareMinToValue(value) >= 0;
+ // we are looking for records where v < someValue
+ if (stats.compareMinToValue(value) >= 0) {
+ // drop if value <= min
+ return BLOCK_CANNOT_MATCH;
+ } else {
+ // if value > min, we must take it
+ return BLOCK_MUST_MATCH;
Review Comment:
If we allow min/max values to be lower/upper bounds and not part of the real
data (as @wgtmac suggested) then there are only two scenarios we can be sure
the requested value is in the row group:
* Searching for `null` and the number of nulls (is specified and) is greater
than `0`
* The min value and the max value are both equal to the value we are
searching for
If we expect min/max values to be part of the row groups then we can extend
the related statements but it might not be a safe choice.
Dictionary filter is much more straightforward. Bloom filter should be used
only if the requested value is not in the dictionary (or there is no dictionary
at all) and there are pages that are not dictionary encoded. So your change
clearly makes sense to differenciate the three potential results and move
forward to bloom filters only in case of `BLOCK_MIGHT_MATCH`.
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