Allow only a fixed-size receive predictor

With this commit we simplify our network layer by only allowing to define a
fixed receive predictor size instead of a minimum and maximum value. This also
means that the following (previously undocumented) settings are removed:

* http.netty.receive_predictor_min
* http.netty.receive_predictor_max

Using an adaptive sizing policy in the receive predictor is a very low-level
optimization. The implications on allocation behavior are extremely hard to grasp
(see our previous work in elastic#23185) and adaptive sizing would only be beneficial
anyway if the message protocol allows very different message sizes (on network
level).

To determine whether these settings are beneficial, we ran the PMC and
nyc_taxis benchmarks from our macrobenchmark suite with various heap
settings (1GB, 2GB, 4GB, 8GB, 16GB). In one scenario we use the fixed
receive predictor size (`http.netty.receive_predictor`) with 16kB, 32kB
and 64kB. We contrasted this with `http.netty.receive_predictor_min` = 16KB and
`http.netty.receive_predictor_max` = 64kB. The results (specifically indexing
throughtput) were identical (accounting for natural run-to-run variance).

In summary, these settings offer no benefit but only add complexity.

docs/reference/migration/migrate_6_0/settings.asciidoc

@@ -70,6 +70,9 @@ The previously unused settings `transport.netty.max_cumulation_buffer_capacity`,
 `transport.netty.max_composite_buffer_components` and
 `http.netty.max_cumulation_buffer_capacity` have been removed.
 
+Also, the settings `http.netty.receive_predictor_min` and
+`http.netty.receive_predictor_max` have been removed.
+
 ==== Similarity settings
 
 The `base` similarity is now ignored as coords and query normalization have

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpServerTransport.java

@@ -22,7 +22,6 @@
 import com.carrotsearch.hppc.IntHashSet;
 import com.carrotsearch.hppc.IntSet;
 import io.netty.bootstrap.ServerBootstrap;
-import io.netty.channel.AdaptiveRecvByteBufAllocator;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
@@ -88,7 +87,6 @@
 import java.util.regex.Pattern;
 
 import static org.elasticsearch.common.settings.Setting.boolSetting;
-import static org.elasticsearch.common.settings.Setting.byteSizeSetting;
 import static org.elasticsearch.common.util.concurrent.EsExecutors.daemonThreadFactory;
 import static org.elasticsearch.http.HttpTransportSettings.SETTING_CORS_ALLOW_CREDENTIALS;
 import static org.elasticsearch.http.HttpTransportSettings.SETTING_CORS_ALLOW_HEADERS;
@@ -138,10 +136,6 @@ public class Netty4HttpServerTransport extends AbstractLifecycleComponent implem
         Setting.byteSizeSetting("http.tcp.receive_buffer_size", NetworkService.TCP_RECEIVE_BUFFER_SIZE, Property.NodeScope);
     public static final Setting<ByteSizeValue> SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_SIZE =
         Setting.byteSizeSetting("http.netty.receive_predictor_size", new ByteSizeValue(64, ByteSizeUnit.KB), Property.NodeScope);
-    public static final Setting<ByteSizeValue> SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MIN =
-        byteSizeSetting("http.netty.receive_predictor_min", SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_SIZE, Property.NodeScope);
-    public static final Setting<ByteSizeValue> SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MAX =
-        byteSizeSetting("http.netty.receive_predictor_max", SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_SIZE, Property.NodeScope);
 
 
     protected final NetworkService networkService;
@@ -233,17 +227,8 @@ public Netty4HttpServerTransport(Settings settings, NetworkService networkServic
         this.tcpReceiveBufferSize = SETTING_HTTP_TCP_RECEIVE_BUFFER_SIZE.get(settings);
         this.detailedErrorsEnabled = SETTING_HTTP_DETAILED_ERRORS_ENABLED.get(settings);
 
-        // See AdaptiveReceiveBufferSizePredictor#DEFAULT_XXX for default values in netty..., we can use higher ones for us, even fixed one
-        ByteSizeValue receivePredictorMin = SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MIN.get(settings);
-        ByteSizeValue receivePredictorMax = SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MAX.get(settings);
-        if (receivePredictorMax.getBytes() == receivePredictorMin.getBytes()) {
-            recvByteBufAllocator = new FixedRecvByteBufAllocator(Math.toIntExact(receivePredictorMax.getBytes()));
-        } else {
-            recvByteBufAllocator = new AdaptiveRecvByteBufAllocator(
-                Math.toIntExact(receivePredictorMin.getBytes()),
-                Math.toIntExact(receivePredictorMin.getBytes()),
-                Math.toIntExact(receivePredictorMax.getBytes()));
-        }
+        ByteSizeValue receivePredictor = SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_SIZE.get(settings);
+        recvByteBufAllocator = new FixedRecvByteBufAllocator(receivePredictor.bytesAsInt());
 
         this.compression = SETTING_HTTP_COMPRESSION.get(settings);
         this.compressionLevel = SETTING_HTTP_COMPRESSION_LEVEL.get(settings);
@@ -259,9 +244,8 @@ public Netty4HttpServerTransport(Settings settings, NetworkService networkServic
         this.maxContentLength = maxContentLength;
 
         logger.debug("using max_chunk_size[{}], max_header_size[{}], max_initial_line_length[{}], max_content_length[{}], " +
-                "receive_predictor[{}->{}], pipelining[{}], pipelining_max_events[{}]",
-            maxChunkSize, maxHeaderSize, maxInitialLineLength, this.maxContentLength,
-            receivePredictorMin, receivePredictorMax, pipelining, pipeliningMaxEvents);
+                "receive_predictor[{}], pipelining[{}], pipelining_max_events[{}]",
+            maxChunkSize, maxHeaderSize, maxInitialLineLength, this.maxContentLength, receivePredictor, pipelining, pipeliningMaxEvents);
     }
 
     public Settings settings() {

modules/transport-netty4/src/main/java/org/elasticsearch/transport/Netty4Plugin.java

@@ -61,8 +61,6 @@ public List<Setting<?>> getSettings() {
             Netty4HttpServerTransport.SETTING_HTTP_TCP_SEND_BUFFER_SIZE,
             Netty4HttpServerTransport.SETTING_HTTP_TCP_RECEIVE_BUFFER_SIZE,
             Netty4HttpServerTransport.SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_SIZE,
-            Netty4HttpServerTransport.SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MIN,
-            Netty4HttpServerTransport.SETTING_HTTP_NETTY_RECEIVE_PREDICTOR_MAX,
             Netty4Transport.WORKER_COUNT,
             Netty4Transport.NETTY_RECEIVE_PREDICTOR_SIZE,
             Netty4Transport.NETTY_RECEIVE_PREDICTOR_MIN,