Account for XContent overhead in in-flight breaker

So far the in-flight request circuit breaker has only accounted for the
on-the-wire representation of a request. However, we convert the raw
request into XContent internally which increases the overhead.
Therefore, we increase the value of the corresponding setting
`network.breaker.inflight_requests.overhead` from one to two. While this
value is still rather conservative (we assume that the representation as
structured objects has no overhead compared to the byte[]), it is closer
to reality than the current value.

Relates #31613

docs/reference/migration/migrate_7_0/indices.asciidoc

@@ -64,3 +64,9 @@ The following previously deprecated url parameter have been removed:
 * `filter_cache` - use `query` instead
 * `request_cache` - use `request` instead
 * `field_data` - use `fielddata` instead
+
+==== `network.breaker.inflight_requests.overhead` increased to 2
+
+Previously the in flight requests circuit breaker considered only the raw byte representation.
+By bumping the value of `network.breaker.inflight_requests.overhead` from 1 to 2, this circuit
+breaker considers now also the memory overhead of representing the request as a structured object.

docs/reference/modules/indices/circuit_breaker.asciidoc

@@ -60,7 +60,9 @@ request) from exceeding a certain amount of memory.
 
 The in flight requests circuit breaker allows Elasticsearch to limit the memory usage of all
 currently active incoming requests on transport or HTTP level from exceeding a certain amount of
-memory on a node. The memory usage is based on the content length of the request itself.
+memory on a node. The memory usage is based on the content length of the request itself. This
+circuit breaker also considers that memory is not only needed for representing the raw request but
+also as a structured object which is reflected by default overhead.
 
 `network.breaker.inflight_requests.limit`::
 
@@ -70,7 +72,7 @@ memory on a node. The memory usage is based on the content length of the request
 `network.breaker.inflight_requests.overhead`::
 
     A constant that all in flight requests estimations are multiplied with to determine a
-    final estimation. Defaults to 1
+    final estimation. Defaults to 2.
 
 [[accounting-circuit-breaker]]
 [float]

server/src/main/java/org/elasticsearch/indices/breaker/HierarchyCircuitBreakerService.java

@@ -73,7 +73,7 @@ public class HierarchyCircuitBreakerService extends CircuitBreakerService {
     public static final Setting<ByteSizeValue> IN_FLIGHT_REQUESTS_CIRCUIT_BREAKER_LIMIT_SETTING =
         Setting.memorySizeSetting("network.breaker.inflight_requests.limit", "100%", Property.Dynamic, Property.NodeScope);
     public static final Setting<Double> IN_FLIGHT_REQUESTS_CIRCUIT_BREAKER_OVERHEAD_SETTING =
-        Setting.doubleSetting("network.breaker.inflight_requests.overhead", 1.0d, 0.0d, Property.Dynamic, Property.NodeScope);
+        Setting.doubleSetting("network.breaker.inflight_requests.overhead", 2.0d, 0.0d, Property.Dynamic, Property.NodeScope);
     public static final Setting<CircuitBreaker.Type> IN_FLIGHT_REQUESTS_CIRCUIT_BREAKER_TYPE_SETTING =
         new Setting<>("network.breaker.inflight_requests.type", "memory", CircuitBreaker.Type::parseValue, Property.NodeScope);
 

server/src/test/java/org/elasticsearch/rest/RestControllerTests.java

@@ -239,7 +239,7 @@ public boolean canTripCircuitBreaker() {
 
     public void testDispatchRequestAddsAndFreesBytesOnSuccess() {
         int contentLength = BREAKER_LIMIT.bytesAsInt();
-        String content = randomAlphaOfLength(contentLength);
+        String content = randomAlphaOfLength((int) Math.round(contentLength / inFlightRequestsBreaker.getOverhead()));
         RestRequest request = testRestRequest("/", content, XContentType.JSON);
         AssertingChannel channel = new AssertingChannel(request, true, RestStatus.OK);
 
@@ -251,7 +251,7 @@ public void testDispatchRequestAddsAndFreesBytesOnSuccess() {
 
     public void testDispatchRequestAddsAndFreesBytesOnError() {
         int contentLength = BREAKER_LIMIT.bytesAsInt();
-        String content = randomAlphaOfLength(contentLength);
+        String content = randomAlphaOfLength((int) Math.round(contentLength / inFlightRequestsBreaker.getOverhead()));
         RestRequest request = testRestRequest("/error", content, XContentType.JSON);
         AssertingChannel channel = new AssertingChannel(request, true, RestStatus.BAD_REQUEST);
 
@@ -263,7 +263,7 @@ public void testDispatchRequestAddsAndFreesBytesOnError() {
 
     public void testDispatchRequestAddsAndFreesBytesOnlyOnceOnError() {
         int contentLength = BREAKER_LIMIT.bytesAsInt();
-        String content = randomAlphaOfLength(contentLength);
+        String content = randomAlphaOfLength((int) Math.round(contentLength / inFlightRequestsBreaker.getOverhead()));
         // we will produce an error in the rest handler and one more when sending the error response
         RestRequest request = testRestRequest("/error", content, XContentType.JSON);
         ExceptionThrowingChannel channel = new ExceptionThrowingChannel(request, true);
@@ -276,7 +276,7 @@ public void testDispatchRequestAddsAndFreesBytesOnlyOnceOnError() {
 
     public void testDispatchRequestLimitsBytes() {
         int contentLength = BREAKER_LIMIT.bytesAsInt() + 1;
-        String content = randomAlphaOfLength(contentLength);
+        String content = randomAlphaOfLength((int) Math.round(contentLength / inFlightRequestsBreaker.getOverhead()));
         RestRequest request = testRestRequest("/", content, XContentType.JSON);
         AssertingChannel channel = new AssertingChannel(request, true, RestStatus.SERVICE_UNAVAILABLE);
 
@@ -287,7 +287,7 @@ public void testDispatchRequestLimitsBytes() {
     }
 
     public void testDispatchRequiresContentTypeForRequestsWithContent() {
-        String content = randomAlphaOfLengthBetween(1, BREAKER_LIMIT.bytesAsInt());
+        String content = randomAlphaOfLength((int) Math.round(BREAKER_LIMIT.getBytes() / inFlightRequestsBreaker.getOverhead()));
         RestRequest request = testRestRequest("/", content, null);
         AssertingChannel channel = new AssertingChannel(request, true, RestStatus.NOT_ACCEPTABLE);
         restController = new RestController(
@@ -312,7 +312,7 @@ public void testDispatchDoesNotRequireContentTypeForRequestsWithoutContent() {
     }
 
     public void testDispatchFailsWithPlainText() {
-        String content = randomAlphaOfLengthBetween(1, BREAKER_LIMIT.bytesAsInt());
+        String content = randomAlphaOfLength((int) Math.round(BREAKER_LIMIT.getBytes() / inFlightRequestsBreaker.getOverhead()));
         FakeRestRequest fakeRestRequest = new FakeRestRequest.Builder(NamedXContentRegistry.EMPTY)
             .withContent(new BytesArray(content), null).withPath("/foo")
             .withHeaders(Collections.singletonMap("Content-Type", Collections.singletonList("text/plain"))).build();
@@ -342,7 +342,7 @@ public void testDispatchUnsupportedContentType() {
 
     public void testDispatchWorksWithNewlineDelimitedJson() {
         final String mimeType = "application/x-ndjson";
-        String content = randomAlphaOfLengthBetween(1, BREAKER_LIMIT.bytesAsInt());
+        String content = randomAlphaOfLength((int) Math.round(BREAKER_LIMIT.getBytes() / inFlightRequestsBreaker.getOverhead()));
         FakeRestRequest fakeRestRequest = new FakeRestRequest.Builder(NamedXContentRegistry.EMPTY)
             .withContent(new BytesArray(content), null).withPath("/foo")
             .withHeaders(Collections.singletonMap("Content-Type", Collections.singletonList(mimeType))).build();
@@ -366,7 +366,7 @@ public boolean supportsContentStream() {
 
     public void testDispatchWithContentStream() {
         final String mimeType = randomFrom("application/json", "application/smile");
-        String content = randomAlphaOfLengthBetween(1, BREAKER_LIMIT.bytesAsInt());
+        String content = randomAlphaOfLength((int) Math.round(BREAKER_LIMIT.getBytes() / inFlightRequestsBreaker.getOverhead()));
         final List<String> contentTypeHeader = Collections.singletonList(mimeType);
         FakeRestRequest fakeRestRequest = new FakeRestRequest.Builder(NamedXContentRegistry.EMPTY)
             .withContent(new BytesArray(content), RestRequest.parseContentType(contentTypeHeader)).withPath("/foo")