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Memcached new features...

posted Nov 15, 2011, 1:57 AM by Kent Bozlinski
There is a new set of changes to MemcacheD. This was originally posted by dormondo here.

Memcached 1.4.10 Release Notes

Date: 2011-11-9


Download Link:


This release is focused on thread scalability and performance improvements. This release should be able to feed data back faster than any network card can support as of this writing.


  • Disable  issue 140 's test.
  • Push cache_lock deeper into item_alloc
  • Use item partitioned lock for as much as possible
  • Remove the depth search from item_alloc
  • Move hash calls outside of cache_lock
  • Use spinlocks for main cache lock
  • Remove uncommon branch from asciiprot hot path
  • Allow all tests to run as root

New Features


For more details, read the commit messages from git. Each change was carefully researched to not increase memory requirements and to be safe from deadlocks. Each change was individually tested via mc-crusher ( to ensure benefits.

Tested improvements in speed between 3 and 6 worker threads (-t 3 to -t 6). More than -t 6 reduced speed.

In my tests, set was raised from 300k/s to around 930k/s. Key fetches/sec (multigets) from 1.6 million/s to around 3.7 million/s for a quadcore box. A machine with more cores was able to pull 6 million keys per second. Incr/Decr performance increased similar to set performance. Non-bulk tests were limited by the packet rate of localhost or the network card.

Multiple NUMA nodes reduces performance (but not enough to really matter). If you want the absolute highest speed, as of this release you can run one instance per numa node (where n is your core count):

numactl --cpunodebind=0 memcached -m 4000 -t n

Older versions of memcached are plenty fast for just about all users. This changeset is to allow more flexibility in future feature additions, as well as improve memcached's overall latency on busy systems.

Keep an eye on your hitrate and performance numbers. Please let us know immediately if you experience any regression from these changes. We have tried to be as thorough as possible in testing, but you never know.


The following people contributed to this release since 1.4.9.

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 1.4.9..1.4.10 or use a web view.