Apply source excludes early when retrieving the _inference_fields

[jimczi]

The inference fields is automatically retrieved when exclude_vectors is set to false. In this change, we apply the source exclude early, in case the _inference_fields is removed, to avoid loading it entirely. We also protect against immutable map when adding the _inference_fields in _source since we cannot ensure that the map is always mutable.

Example stack trace:

Failed to execute phase [fetch], all shards failed; shardFailures {[<id>][<index>][0]: org.elasticsearch.transport.RemoteTransportException: [<node>][<ip-address>:9300][indices:data/read/search[phase/fetch/id]]
Caused by: org.elasticsearch.search.fetch.FetchPhaseExecutionException: Fetch Failed [Error running fetch phase for doc [1]]
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.FetchPhaseDocsIterator.iterate(FetchPhaseDocsIterator.java:109)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.FetchPhase.buildSearchHits(FetchPhase.java:248)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.FetchPhase.execute(FetchPhase.java:91)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.SearchService.lambda$executeFetchPhase$16(SearchService.java:1212)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.action.ActionRunnable$3.accept(ActionRunnable.java:79)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.action.ActionRunnable$3.accept(ActionRunnable.java:76)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.action.ActionRunnable$4.doRun(ActionRunnable.java:101)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.TimedRunnable.doRun(TimedRunnable.java:35)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingAbstractRunnable.doRun(ThreadContext.java:1067)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:27)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1090)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:614)
	at java.base/java.lang.Thread.run(Thread.java:1474)
Caused by: java.lang.UnsupportedOperationException
	at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:159)
	at java.base/java.util.ImmutableCollections$AbstractImmutableMap.put(ImmutableCollections.java:1318)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.subphase.FetchSourcePhase$1.replaceInferenceMetadataFields(FetchSourcePhase.java:102)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.subphase.FetchSourcePhase$1.hitExecute(FetchSourcePhase.java:83)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.subphase.FetchSourcePhase$1.process(FetchSourcePhase.java:58)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.FetchPhase$1.nextDoc(FetchPhase.java:231)
	at org.elasticsearch.server@9.2.0/org.elasticsearch.search.fetch.FetchPhaseDocsIterator.iterate(FetchPhaseDocsIterator.java:90)
	... 13 more

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

Hi @jimczi, I've created a changelog YAML for you.

[pmpailis]

LGTM! Should we also update docs clarifying how exclude_vectors interacts with include/exclude?

[jimczi]

Should we also update docs clarifying how exclude_vectors interacts with include/exclude?

I'll open a follow up pr, thanks

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	9.2