= raindrops - real-time stats for preforking Rack servers

raindrops is a real-time stats toolkit to show statistics for Rack HTTP
servers.  It is designed for preforking servers such as unicorn, but
should support any Rack HTTP server on platforms supporting POSIX shared
memory.  It may also be used as a generic scoreboard for sharing atomic
counters across multiple processes.

== Features

* counters are shared across all forked children and lock-free

* counters are kept on separate cache lines to reduce contention under SMP

* may expose server statistics as a Rack Middleware endpoint
  (default: "/_raindrops")

* middleware displays the number of actively processing and writing
  clients from a single request regardless of which worker process
  it hits.

== Linux-only Extra Features!

* Middleware response includes extra stats for bound TCP and
  Unix domain sockets (configurable, it can include stats from
  other TCP or UNIX domain socket servers).

* TCP socket stats use efficient inet_diag facilities via netlink
  instead of parsing /proc/net/tcp to minimize overhead.
  This was fun to discover and write.

* TCP_Info reporting may be used to check stat for every accepted client
  on TCP servers

Users of older Linux kernels need to ensure that the the "inet_diag"
and "tcp_diag" kernel modules are loaded as they do not autoload correctly

== Install

We recommend GCC 4+ (or compatible) to support the __sync builtins
(__sync_{add,sub}_and_fetch()):

https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html

For non-GCC 4+ users, we also support compilation with the libatomic_ops
package starting with Raindrops 0.4.0:

https://github.com/ivmai/libatomic_ops

If you're using a packaged Ruby distribution, make sure you have a C
compiler and the matching Ruby development libraries and headers.

If you use RubyGems:

    gem install raindrops

== Usage

See Raindrops::Middleware and Raindrops::LastDataRecv documentation for
use Rack servers.  The entire library is fully-documented and we are
responsive on the mailing list (mailto:raindrops-public@bogomips.org) if
you have any questions or comments.

== Development

You can get the latest source via git from the following locations:

  git://bogomips.org/raindrops.git
  git://repo.or.cz/raindrops.git (mirror)

You may browse the code from the web and download the latest snapshot
tarballs here:

* https://bogomips.org/raindrops.git
* http://repo.or.cz/w/raindrops.git (gitweb)

Inline patches (from "git format-patch") to the mailing list are
preferred because they allow code review and comments in the reply to
the patch.

We will adhere to mostly the same conventions for patch submissions as
git itself.  See the Documentation/SubmittingPatches document
distributed with git on on patch submission guidelines to follow.  Just
don't email the git mailing list or maintainer with raindrops patches.

raindrops is licensed under the LGPL-2.1+

== Contact

All feedback (bug reports, user/development discussion, patches, pull
requests) go to the mailing list: mailto:raindrops-public@bogomips.org

Mailing list archives are available over HTTPS and NNTP:

* https://bogomips.org/raindrops-public/
* nntp://news.public-inbox.org/inbox.comp.lang.ruby.raindrops
