Release Notes for Memcached 1.3 beta 2

mc-1.3.2-release-notes.txt

                  Memcached 1.3 Beta 2 Release Notes
                  ==================================

Date: 2009-03-11 Wed


Table of Contents
=================
1 New Features
    1.1 Binary Protocol
        1.1.1 Client Availability
    1.2 Performance
    1.3 Stats
        1.3.1 New Stats
        1.3.2 More Granular Stats
        1.3.3 Removed stats
2 Bug Fixes
3 Development Info
4 Feedback
5 Contributors


1 New Features
~~~~~~~~~~~~~~~

1.1 Binary Protocol
====================

A new feature that brings new features.  We now have goodness like
CAS-everywhere (e.g. delete), silent, but verifiable mutation
commands, and many other wonders.

Note that the original protocol is *not* deprecated.  It will be
supported indefinitely, although some new features may only be
available in the binary protocol.

1.1.1 Client Availability
--------------------------

Many clients for the binary protocol are available.

* C

  libmemcached supports just about anything you can do with a memcached
  protocol and is the foundation for many clients in many different
  languages (which you can find linked from the project page).

  Project page:  [http://tangent.org/552/libmemcached.html]

* Java

  spymemcached has very good text and binary protocol support over IPv4
  and IPv6 with a quite comprehensive test suite.

  Project page:  [http://code.google.com/p/spymemcached/]

* Protocol Spec

  NIH problem?  Go write your own client.  :)

  [http://cloud.github.com/downloads/dustin/memcached/protocol-binary.txt]


1.2 Performance
================

Lots of effort has gone into increasing performance.

There is no longer a build-time distinction between a single-threaded
and multi-threaded memcached.  If you want a single-threaded
memcached, ask for one thread (though there'll still be utility
threads and other such things in the background).  This change lets us
focus on a future where multiple cores can be saturated for servicing
requests.

Facebook-inspired contention reduction with per-thread stat collection
and the Facebook connection dispatch and thread starvation prevention
contributions helped our scalability.

Lock analysis also showed us that we had quite a bit of contention on
hash table expansion which has been moved into its own thread, greatly
improving the scalability on multicore hardware.

A variety of smaller things also shook out of performance testing and
analysis.

There's also a memory optimization for users who don't actually make
use of CAS.  Running memcached with -C disables the use of CAS
resulting in a savings of about eight bytes per item.  If you have big
caches, and don't use CAS, this can lead to a considerable savings.

1.3 Stats
==========

There are several new stats and some new ways to look at older stats.

1.3.1 New Stats
----------------

* Delete

  The global stats now contain statistics on deletion.

  delete_hits refers to the number of times a deletion command was
  issued which resulted in a modification of the cache while
  delete_misses refers to the number of times a deletion command was
  issued which had no effect due to a key mismatch.

* Incr/Decr

  Incr and decr each have a pair of stats showing when a
  successful/unsuccessful incr occurred.  incr_hits, incr_misses,
  decr_hits, and decr_misses show where such mutations worked and where
  they failed to find an existing object to mutate.

* CAS

  CAS stats are tracked in three different ways:

  + cas_hits

    Number of attempts to CAS in a new value that worked.

  + cas_misses

    Number of attempts to CAS in a value where the key was not found.

  + cas_badval

    Number of attempts to CAS in a value where the CAS failed due to the
    object changing between the gets and the update.

* slab class evicted time

  Per slab class, you can now see how recently accessed the most recent
  evicted data was.  This is a useful gauge to determine eviction
  velocity on a slab so you can know whether evictions are healthy or if
  you've got a problem.


1.3.2 More Granular Stats
--------------------------

Where possible, stats are now tracked individually by slab class.  The
following stats are available on a per-slab-class basis (via "stats slabs"):

  * get_hits
  * cmd_set
  * delete_hits
  * incr_hits
  * decr_hits
  * cas_hits
  * cas_badval

(misses are obviously not available as they refer to a non-existent item)

1.3.3 Removed stats
--------------------

"stats malloc" and "stats maps" have been removed.

If you depended on these commands for anything, please let us know so
we can bring them back in a more maintainable way.

2 Bug Fixes
~~~~~~~~~~~~

  * Build fixes on ubuntu (gcc and icc) and FreeBSD
  * bad interaction with cas + incr (bug 15)
  * setuid failures are reported properly at daemonization time
  * decr overflow causing unnecessary truncation to 0 (bug 21)
  * failure to bind on Linux with no network (i.e. laptop dev)
  * some memcached-tool cleanup

3 Development Info
~~~~~~~~~~~~~~~~~~~

We've added a bunch of tests and new code coverage reports.

All included code in this release has been tested against the
following platforms (using the in-tree test suite):

  * ubuntu 8.10 (64-bit, both gcc and icc)
  * ubuntu 8.04 (32-bit)
  * OS X 10.5 (ppc and intel)
  * OpenSolaris 5.11 x86 (with and without dtrace)
  * FreeBSD 7 x86

4 Feedback
~~~~~~~~~~~

Please try this version.  Make it suffer.  Report feedback to the list
or file bugs as you find them.

  * Mailing List:  [http://groups.google.com/group/memcached]
  * Issue Tracker:  [http://code.google.com/p/memcached/issues/list]
  * IRC:  #memcached on freenode

5 Contributors
~~~~~~~~~~~~~~~

The following people contributed to this release since 1.2.6.

Note that this is based on who contributed changes, not how they were
done.  In many cases, a code snippet on the mailing list or a bug
report ended up as a commit with your name on it.

Note that this is just a summary of how many changes each person made
which doesn't necessarily reflect how significant each change was.
For details on what led up into a branch, either grab the git repo and
look at the output of `git log 1.2.6..1.3.2` or use a web view.

  * Repo list:  [http://code.google.com/p/memcached/wiki/DevelopmentRepos]
  * Web View: [http://github.com/dustin/memcached/commits/1.3.2]

  104  Dustin Sallings
   49  Trond Norbye
   32  Toru Maesaka
   31  dormando
    8  Steve Yen
    7  hachi
    6  Aaron Stone
    6  Brian Aker
    4  Victor Kirkebo
    2  Ricky Zhou
    1  Jonathan Bastien-Filiatrault
    1  Evan Klitzke
    1  Eric Lambert