ChrisHegarty commented on code in PR #13196:
URL: https://github.com/apache/lucene/pull/13196#discussion_r1535291132
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lucene/core/src/java21/org/apache/lucene/store/MemorySegmentIndexInputProvider.java:
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@@ -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:
> when you merge segments you certainly always want to read the files with
sequential advise
I've not yet checked, but is `Context.MERGE` set when merging HNSW graphs?
(which would favour random access)
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