Add instructions about Java9IntHash

Author: lhotari

docs/client-libraries-java-setup.md

@@ -184,4 +184,12 @@ To enable this feature in Java clients since Java 11, you need to add the follow
 In addition, you need to add one of the following JVM options:
 
 - `-Dorg.apache.pulsar.shade.io.netty.tryReflectionSetAccessible=true` for the default shaded Pulsar client
-- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+
+### Enabling optimized checksum calculation when native library loading fails
+
+The Pulsar Java client uses `com.scurrilous.circe.checksum.Crc32cIntChecksum` class from the BookKeeper client for checksum calculation. For optimized checksum calculation Pulsar attempts to load `libcirce-checksum` native library. When that isn't available, `com.scurrilous.circe.checksum.Java9IntHash` class is used.
+This only works when `--add-opens java.base/java.util.zip=ALL-UNNAMED` is passed in the JVM options.
+The error message will be `Unable to use reflected methods:
+java.lang.reflect.InaccessibleObjectException: Unable to make private static int java.util.zip.CRC32C.updateBytes(int,byte[],int,int) accessible: module java.base does not "opens java.util.zip" to unnamed module` when the required JVM option is missing
+

versioned_docs/version-3.0.x/client-libraries-java-setup.md

@@ -88,4 +88,12 @@ To enable this feature in Java clients since Java 11, you need to add the follow
 In addition, you need to add one of the following JVM options:
 
 - `-Dorg.apache.pulsar.shade.io.netty.tryReflectionSetAccessible=true` for the default shaded Pulsar client
-- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+
+### Enabling optimized checksum calculation when native library loading fails
+
+The Pulsar Java client uses `com.scurrilous.circe.checksum.Crc32cIntChecksum` class from the BookKeeper client for checksum calculation. For optimized checksum calculation Pulsar attempts to load `libcirce-checksum` native library. When that isn't available, `com.scurrilous.circe.checksum.Java9IntHash` class is used.
+This only works when `--add-opens java.base/java.util.zip=ALL-UNNAMED` is passed in the JVM options.
+The error message will be `Unable to use reflected methods:
+java.lang.reflect.InaccessibleObjectException: Unable to make private static int java.util.zip.CRC32C.updateBytes(int,byte[],int,int) accessible: module java.base does not "opens java.util.zip" to unnamed module` when the required JVM option is missing
+

versioned_docs/version-4.0.x/client-libraries-java-setup.md

@@ -184,4 +184,12 @@ To enable this feature in Java clients since Java 11, you need to add the follow
 In addition, you need to add one of the following JVM options:
 
 - `-Dorg.apache.pulsar.shade.io.netty.tryReflectionSetAccessible=true` for the default shaded Pulsar client
-- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+- `-Dio.netty.tryReflectionSetAccessible=true` for the unshaded "original" Pulsar client
+
+### Enabling optimized checksum calculation when native library loading fails
+
+The Pulsar Java client uses `com.scurrilous.circe.checksum.Crc32cIntChecksum` class from the BookKeeper client for checksum calculation. For optimized checksum calculation Pulsar attempts to load `libcirce-checksum` native library. When that isn't available, `com.scurrilous.circe.checksum.Java9IntHash` class is used.
+This only works when `--add-opens java.base/java.util.zip=ALL-UNNAMED` is passed in the JVM options.
+The error message will be `Unable to use reflected methods:
+java.lang.reflect.InaccessibleObjectException: Unable to make private static int java.util.zip.CRC32C.updateBytes(int,byte[],int,int) accessible: module java.base does not "opens java.util.zip" to unnamed module` when the required JVM option is missing
+