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
) is private.
