memcached and streaming

[Maxim Dounin]

Hello!

On Sun, Feb 03, 2008 at 05:32:16PM +0300, Tomash Brechko wrote:

>Hello,
>
>In memcached.c there's a line,
>
>  setsockopt(sfd, IPPROTO_TCP, TCP_NODELAY, (void *)&flags, sizeof(flags));
>
>We should realise that this is a serious performance killer for
>streaming.  For instance, C::M::F has multi-update commands that are
>capable to bundle several requests into one network packet.  However
>replies are always sent _one at a time_.  I.e. tons of packets with
>single 'STORED' etc. (>40 bytes header and 6 bytes of data---not the
>best ratio).  Not to say the the greater number of packets means a
>huge increase of latency in a congested network.
>
>memcached should have in its TODO "Disable TCP_NODELAY and enable
>TCP_CORK/TCP_NOPUSH for streaming".  The server may tell if the

Just a quick note: the code to set/clear TCP_NOPUSH was here 
before iov work was merged from facebook at r320 (i.e. in 1.1.* 
branch).

Maxim Dounin