[BUG] Timestamp sort optimizations don't work on searchable snapshot or segrep replicas

[msfroh]

Describe the bug

Diving through some code to understand performance regressions in descending sort on timestamp ahead of OpenSearch 3.0, I finally understood the change added in #7967.

Essentially, we apply a sort to the IndexWriterConfig to say that any IndexReader opened from the IndexWriter should have its segments sorted by descending max timestamp. Unfortunately, that only happens in InternalEngine.

We have other engine types, ReadOnlyEngine and NRTReplicationEngine, which don't even have an IndexWriter (since neither is capable of writing Lucene indexes). The sort ordering optimization is not applied to them.

We should push the leafSorter (via the EngineConfig) into these other engines, so that they can pass them to the their DirectoryReader.open calls.

Related component

Search:Performance

To Reproduce

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Expected behavior

See above.

Additional Details

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[msfroh]

Relevant lines where the IndexReaders get opened for the other engine types:

OpenSearch/server/src/main/java/org/opensearch/index/engine/NRTReplicationReaderManager.java

Line 78 in 4319f2b

DirectoryReader innerReader = StandardDirectoryReader.open(referenceToRefresh.directory(), currentInfos, subs, null);

OpenSearch/server/src/main/java/org/opensearch/index/engine/ReadOnlyEngine.java

Line 217 in a1a1596

reader = DirectoryReader.open(commit, this.minimumSupportedVersion.luceneVersion.major, null);

OpenSearch/server/src/main/java/org/opensearch/index/engine/ReadOnlyEngine.java

Line 219 in a1a1596

reader = DirectoryReader.open(commit);

In the first two cases, the final null parameter should be the leafSorter. In the third case, we need to either use StandardDirectoryReader or we should change it to:

reader = DirectoryReader.open(commit, Version.CURRENT.minimumCompatibilityVersion().luceneVersion.major, config().getLeafSorter());