Unnecessary multiple requests with the same esagg query

[ppisljar]

Unnecessary multiple requests with the same esagg query

When a search is sent to ES and a response is received, the search service is looking if the request needs a post-flight request.

kibana/src/plugins/data/common/search/search_source/search_source.ts

Lines 539 to 548 in 74fdd1b

	if (!this.hasPostFlightRequests()) {
	obs.next(this.postFlightTransform(response));
	obs.complete();
	} else {
	// Treat the complete response as partial, then run the postFlightRequests.
	obs.next({
	...this.postFlightTransform(response),
	isPartial: true,
	isRunning: true,
	});

If needed, it transforms the response to a partial response and update the body with the postflight request.
This works correctly if the postflight is actually necessary, but due to the current implementation the postflight request is always "applied" even if not needed, causing a subsequent request to be sent to ES.
This results to an increase of:

• more time spent unnecessary before returning the results to the client
• 1 more unnecessary search strategy that cache check
• 1 more unnecessary run of tabify

Analysis
The current method that checks if a request needs a subsequent post-flight request relies on a loose check from the function hasPostFlightRequests. This function checks if the agg property type.postFlightRequest is a function.

kibana/src/plugins/data/common/search/search_source/search_source.ts

Lines 474 to 483 in 74fdd1b

	private hasPostFlightRequests() {
	const aggs = this.getField('aggs');
	if (aggs instanceof AggConfigs) {
	return aggs.aggs.some(
	(agg) => agg.enabled && typeof agg.type.postFlightRequest === 'function'
	);
	} else {
	return false;
	}
	}

This function is there even if is not required. For example in a terms aggregation without the other bucket the function is still there but just return its identity

kibana/src/plugins/data/common/search/aggs/buckets/terms.ts

Line 93 in 74fdd1b

postFlightRequest: createOtherBucketPostFlightRequest(constructSingleTermOtherFilter),

All the other cases this is defaulted to an identity function, so the hasPostFlightRequests function will always return true.

kibana/src/plugins/data/common/search/aggs/agg_type.ts

Line 311 in 74fdd1b

this.postFlightRequest = config.postFlightRequest || identity;

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)