thecoop commented on code in PR #14510:
URL: https://github.com/apache/lucene/pull/14510#discussion_r2071743905
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lucene/core/src/java/org/apache/lucene/store/MMapDirectory.java:
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@@ -277,6 +277,32 @@ public final long getMaxChunkSize() {
return 1L << chunkSizePower;
}
+ public static ReadAdvice toReadAdvice(IOContext context) {
+ if (context.context() == IOContext.Context.MERGE
+ || context.context() == IOContext.Context.FLUSH) {
+ return ReadAdvice.SEQUENTIAL;
+ }
+
+ if (context.hints().contains(DataAccessHint.RANDOM)) {
+ return ReadAdvice.RANDOM;
+ }
+ if (context.hints().contains(DataAccessHint.SEQUENTIAL)) {
+ return ReadAdvice.SEQUENTIAL;
+ }
+
+ if (context.hints().contains(FileTypeHint.DATA)
+ || context.hints().contains(FileTypeHint.INDEX)) {
+ return ReadAdvice.NORMAL;
+ }
+ // Postings have a forward-only access pattern, so pass ReadAdvice.NORMAL
to perform
+ // readahead.
+ if (context.hints().contains(FileDataHint.POSTINGS)) {
+ return ReadAdvice.NORMAL;
+ }
Review Comment:
Currently, `ReadAdvice.NORMAL` doesn't have a corresponding
`DataAccessHint`, so you get that by not specifying the `DataAccessHint` but
then as the default is now `ReadAdvice.RANDOM` (or configurable), you need some
way to explicitly specify 'I want the OS default behaviour here'.
Maybe we do have a `DataAccessHint.DEFAULT`, but then doesn't
`DataAccessHint` just mirror `ReadAdvice`?
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