dormando edited this page May 18, 2016 · 2 revisions

Memcached 1.3 Beta 2 Release Notes

Date: 2009-03-11 Wed

New Features

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.

==== Client Availability ===

Many clients for the binary protocol are available.


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.


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

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.

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)

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.

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

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


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


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.

  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