magibney commented on code in PR #13570:
URL: https://github.com/apache/lucene/pull/13570#discussion_r1681711345
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lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java:
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@@ -83,6 +86,19 @@ public class MMapDirectory extends FSDirectory {
*/
public static final BiPredicate<String, IOContext> NO_FILES = (filename,
context) -> false;
+ /** Argument for {@link #setGroupingFunction(Function)} that configures no
grouping. */
+ public static final Function<String, Optional<String>> NO_GROUPING =
filename -> Optional.empty();
+
+ /** Argument for {@link #setGroupingFunction(Function)} that configures
grouping by segment. */
+ public static final Function<String, Optional<String>> GROUP_BY_SEGMENT =
+ filename -> {
+ String segmentName = IndexFileNames.parseSegmentName(filename);
+ if (filename.length() == segmentName.length()) {
+ return Optional.empty();
+ }
+ return Optional.of(segmentName);
+ };
Review Comment:
I think Uwe had floated the idea of doing extra validation that we're
actually getting a segment name -- e.g. something like:
```java
String segmentPrefix = IndexFileNames.parseSegmentName(filename);
int segmentPrefixLength = segmentPrefix.length();
if (segmentPrefixLength > 1 && segmentPrefixLength != filename.length() &&
segmentName.charAt(0) == '_') {
String segmentName = segmentPrefix.substring(1);
try {
// try to parse a proper segment identifier
Long.parseLong(segmentName, Character.MAX_RADIX);
return Optional.of(segmentName);
} catch (NumberFormatException ex) {
// unable to parse as a segment identifier
}
}
return Optional.empty();
```
If we can account for all explicit exceptions (where we don't expect to be
able to parse a segment name) we could even throw `IllegalArgumentException`
here instead of returning `Optional.empty()`? (this would prevent grouping from
being used in cases where it should not be, by failing hard -- and could be a
good complement to ensuring `READ_ONCE` is used where appropriate).
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