## What changes were proposed in this pull request?
Initialize SaslEncryption$EncryptedMessage.byteChannel lazily,
so that empty, not yet used instances of ByteArrayWritableChannel
referenced by this field don't use up memory.
I analyzed a heap dump from Yarn Node Manager where this code is used, and found that there are over 40,000 of the above objects in memory, each with a big empty byte[] array. The reason they are all there is because of Netty queued up a large number of messages in memory before transferTo() is called. There is a small number of netty ChannelOutboundBuffer objects, and then collectively , via linked lists starting from their flushedEntry data fields, they end up referencing over 40K ChannelOutboundBuffer$Entry objects, which ultimately reference EncryptedMessage objects.
## How was this patch tested?
Ran all the tests locally.
Author: Misha Dmitriev <misha@cloudera.com>
Closes#21811 from countmdm/misha/spark-24801.
094aa59715