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I am working with Netty 4. I see folowing options of Netty server: WRITE_BUFFER_HIGH_WATER_MARK and WRITE_BUFFER_LOW_WATER_MARK.
The official page
has link to . One of slides looks like this:
ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap.childOption(ChannelOption.WRITE_BUFFER_HIGH_WATER_MARK, 32 * 1024);
bootstrap.childOption(ChannelOption.WRITE_BUFFER_LOW_WATER_MARK, 8 * 1024);
and has this preface:
Set sane WRITE_BUFFER_HIGH_WATER_MARK and WRITE_BUFFER_LOW_WATER_MARK
But what is it WRITE_BUFFER_HIGH_WATER_MARK and WRITE_BUFFER_LOW_WATER_MARK? And how to set them to be sane?
I did not find any clear information. Thanks for your help.
Some information about watermarks from
For instance, imagine you have a queue of tasks on server side that is
filled by clients and processed by backend. In case clients send tasks
too quick the length of the queue grows. One needs to introduce so
named high watermark and low watermark. If queue length is greater
than high watermark stop reading from sockets and queue length will
decrease. When queue length becomes less than low watermark start
reading tasks from sockets again.
Note, to make it possible for clients to adapt to speed you process
tasks (actually to adapt window size) one shouldn't make a big gap
between high and low watermarks. From the other side small gap means
you'll be too often add/remove sockets from the event loop.
For Netty it seems to be true, because
JavaDoc for ChannelConfig says:
If the number of bytes queued in the write buffer exceeds writeBufferHighWaterMark value,
Channel.isWritable() will start to return false.
And for low watermark:
Once the number of bytes queued in the write buffer exceeded the high
water mark and then dropped down below this value,
Channel.isWritable() will return true again.
About sanity, I think, it is relative question, that depends on information that you are sending through the channel and how often. There is no strict rules for what values you must define for that variables. So, I think, you must found your own values in practice. Slides show you one of the examples for that.
5,51832344
WRITE_BUFFER_HIGH_WATER_MARK and WRITE_BUFFER_LOW_WATER_MARK
options and relative methods in ChannelConfig are deprecated.
.option(ChannelOption.WRITE_BUFFER_WATER_MARK, new
WriteBufferWaterMark(1, 2))
that's how you do it.
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