Change tcp_nodelay config to be true (#4986)

* Change tcp_nodelay config

* Update changelog.md

* Update CHANGELOG.md for version

Author: milindl

Diff for: CHANGELOG.md

@@ -37,6 +37,8 @@ librdkafka v2.9.0 is a feature release:
    becomes reachable again (#4970).
  * Remove a one second wait after a partition fetch is restarted following a
    leader change and offset validation (#4970).
+ * Fix the Nagle algorithm (TCP_NODELAY) on broker sockets to not be enabled
+   by default (#4986).
 
 
 ## Fixes
@@ -99,6 +101,12 @@ librdkafka v2.9.0 is a feature release:
    the broker the request is enqueued on is up again.
    Solved by not retrying these kinds of metadata requests.
    Happens since 1.x (#4970).
+ * The Nagle algorithm (TCP_NODELAY) is now disabled by default. It caused a
+   large increase in latency for some use cases, for example, when using an
+   SSL connection.
+   For efficient batching, the application should use `linger.ms`,
+   `batch.size` etc.
+   Happens since: 0.x (#4986).
 
 ### Consumer fixes
 

Diff for: CONFIGURATION.md

@@ -26,7 +26,7 @@ socket.blocking.max.ms                   |  *  | 1 .. 60000      |          1000
 socket.send.buffer.bytes                 |  *  | 0 .. 100000000  |             0 | low        | Broker socket send buffer size. System default is used if 0. <br>*Type: integer*
 socket.receive.buffer.bytes              |  *  | 0 .. 100000000  |             0 | low        | Broker socket receive buffer size. System default is used if 0. <br>*Type: integer*
 socket.keepalive.enable                  |  *  | true, false     |         false | low        | Enable TCP keep-alives (SO_KEEPALIVE) on broker sockets <br>*Type: boolean*
-socket.nagle.disable                     |  *  | true, false     |         false | low        | Disable the Nagle algorithm (TCP_NODELAY) on broker sockets. <br>*Type: boolean*
+socket.nagle.disable                     |  *  | true, false     |          true | low        | Disable the Nagle algorithm (TCP_NODELAY) on broker sockets. <br>*Type: boolean*
 socket.max.fails                         |  *  | 0 .. 1000000    |             1 | low        | Disconnect from broker when this number of send failures (e.g., timed out requests) is reached. Disable with 0. WARNING: It is highly recommended to leave this setting at its default value of 1 to avoid the client and broker to become desynchronized in case of request timeouts. NOTE: The connection is automatically re-established. <br>*Type: integer*
 broker.address.ttl                       |  *  | 0 .. 86400000   |          1000 | low        | How long to cache the broker address resolving results (milliseconds). <br>*Type: integer*
 broker.address.family                    |  *  | any, v4, v6     |           any | low        | Allowed broker IP address families: any, v4, v6 <br>*Type: enum value*

Diff for: src/rdkafka_conf.c

@@ -555,7 +555,7 @@ static const struct rd_kafka_property rd_kafka_properties[] = {
 #endif
     },
     {_RK_GLOBAL, "socket.nagle.disable", _RK_C_BOOL, _RK(socket_nagle_disable),
-     "Disable the Nagle algorithm (TCP_NODELAY) on broker sockets.", 0, 1, 0
+     "Disable the Nagle algorithm (TCP_NODELAY) on broker sockets.", 0, 1, 1
 #ifndef TCP_NODELAY
      ,
      .unsupported = "TCP_NODELAY not available at build time"