Re: [naviserver-devel] Questions about NS details... (scalability, lib changes)

[Vlad S. <vl...@cr...>]

I could be wrong, never used sendfile before.

The code you can check is driver.c, WriterThread, and bufsize parameter 
can be used to define buffer.

I was considering using mmap, but somewhere i heard that too many 
mmapped files could be a problem for the server.

Mike wrote:
>> Async IO i mean, writer thread does loop and sends as much as possible
>> chunks from the files, same way as driver thread reads multiple chunks
>> of requests from multiple clients. sendfile blocks, so you will need 10
>> threads for 10 clients at the same time, in case of writer thread, it
>> can alone transfer 10 files to 10 clients. May be it will be slower in
>> each single case comparing to sendfile but overall it does it fast enough.
> 
> Vlad,
> Sorry, but your assertion is not correct.  sendfile() is not required
> to block - as far as I am aware it works on non-blocking sockets
> without a problem.  The key advantages of using sendfile is that it is
> implemented zero-copy and allows the OS to do large-block read-ahead
> on the files.  If serving 100 clients 650MB files, using non-blocking
> IO read+write needs to allocate local buffers.  If buffers are small
> (e.g. 100KB) then the disk has to seek like crazy from file to file,
> and that will kill performance.  If the buffers are large (e.g. 16MB)
> then the disk seek will be fine but I will need to burn 1.6GB of RAM
> for the buffers in the NS process...  How does NS decide what this
> buffer size is?  Can you point me at the code that performs this
> operation?  How challenging would it be to add optional sendfile
> support here?
> 
> 
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-- 
Vlad Seryakov
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vl...@cr...
http://www.crystalballinc.com/vlad/