uschindler commented on code in PR #13196:
URL: https://github.com/apache/lucene/pull/13196#discussion_r1535248163
##########
lucene/core/src/java21/org/apache/lucene/store/MemorySegmentIndexInputProvider.java:
##########
@@ -92,10 +110,22 @@ private final MemorySegment[] map(
}
if (preload) {
segment.load();
+ } else if (segSize > 0L && advice.isPresent()) { // not when preloading!
+ nativeAccess.madvise(segment, advice.getAsInt());
}
segments[segNr] = segment;
startOffset += segSize;
}
return segments;
}
+
+ private OptionalInt mapContextToMadvise(IOContext context) {
+ if (context.randomAccess) {
+ return OptionalInt.of(NativeAccess.POSIX_MADV_RANDOM);
+ }
+ if (context.readOnce || context.context == Context.MERGE) {
Review Comment:
I think we should move the Context.MERGE check to be the first one, because
when you merge segments you certainly always want to read the files with
sequential advise (although the actual access may be random to a certain
degree), because POSIX_MADV_SEQUENTIAL tells in its documentation: "Hence,
pages in this region can be aggressively read ahead, and **may be freed soon
after they are accessed**."
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