Memcached Memcached 1.4.23 & 1.4.24 Released

eva2000 · Apr 23, 2015

Memcached 1.4.23 has been released https://code.google.com/p/memcached/wiki/ReleaseNotes1423

Overview
Major new release with a complete overhaul of the LRU system. Potentially huge benefits in memory efficiency are possible if the new features are enabled. By default the code should behave similar to how it did in all previous versions, though locking is improved and the new code is still used in some ways.

Please read the feature notes carefully and try it out!

Real world examples have shown huge memory efficiency increases when using items of mixed TTL's (some short, some long). When all items have unlimited TTLs, hit ratios have still improved by several percent.

Fixes

spinlocks removed since they never seem to improve performance.

flush_all was not thread safe.

better handle items refcounted in tail by unlinking them from the LRU's

New Features
This release is a reworking of memcached's core LRU algorithm.

global cache_lock is gone, LRU's are now independently locked.

LRU's are now split between HOT, WARM, and COLD LRU's. New items enter the HOT LRU.

LRU updates only happen as items reach the bottom of an LRU. If active in HOT, stay in HOT, if active in WARM, stay in WARM. If active in COLD, move to WARM.

HOT/WARM each capped at 32% of memory available for that slab class. COLD is uncapped.

Items flow from HOT/WARM into COLD.

A background thread exists which shuffles items between/within the LRU's as capacities are reached.

The primary goal is to better protect active items from "scanning". items which are never hit again will flow from HOT, through COLD, and out the bottom. Items occasionally active (reaching COLD, but being hit before eviction), move to WARM. There they can stay relatively protected.

A secondary goal is to improve latency. The LRU locks are no longer used on item reads, only during sets and from the background thread. Also the background thread is likely to find expired items and release them back to the slab class asynchronously, which speeds up new allocations. Further work on the thread should improve this.
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eva2000 · Apr 23, 2015

Note reported crashes with Memcached 1.4.23 at Google Groups

rdan · Apr 24, 2015

eva2000 said: ↑

Note reported crashes with Memcached 1.4.23 at Google Groups
Click to expand...

Blocker for me to do an upgrade.

eva2000 · Apr 25, 2015

RoldanLT said: ↑

Blocker for me to do an upgrade.
Click to expand...

looks like they might have fixed it Google Groups - Issue 403 - memcached - Memcached 1.4.23 crashes on stats command - Memcached - Google Project Hosting

edit: looks like only fixed in master branch Commits · memcached/memcached · GitHub

not fixed in 1.4.23 Commits · memcached/memcached · GitHub

rdan · Apr 25, 2015

But how to track if it's already push into the package?
With the status Accepted ?

eva2000 · Apr 25, 2015

fix is only in master branch fix major off by one issue · memcached/memcached@369845f · GitHub

line 80 of memcached.h

change from
Code:
#define POWER_LARGEST  255
to
Code:
#define POWER_LARGEST  256 /* actual cap is 255 */

rdan · Apr 25, 2015

And centminmod installer grabs from github repo master branch?

eva2000 · Apr 25, 2015

RoldanLT said: ↑

And centminmod installer grabs from github repo master branch?
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nope from memcached.org listed link line 199 of inc/downloadlinks.inc for .08 beta 02 centminmod/downloadlinks.inc at 123.08centos7beta02 · centminmod/centminmod · GitHub

probably just wait as they'll probably release 1.4.24 or 1.4.23a or something

rdan · Apr 26, 2015

Memcached 1.4.24 is already available, and I'm using it on my Live Server now.

eva2000 · Apr 26, 2015

RoldanLT said: ↑

Memcached 1.4.24 is already available, and I'm using it on my Live Server now.
Click to expand...

excellent Memcached server 1.4.24 default for .08 beta · centminmod/centminmod@148f044 · GitHub

ReleaseNotes1424 - memcached - Release notes for Release 1.4.24 - Memcached - Google Project Hosting

Overview
Bugfix release to replace 1.4.23. If you tried 1.4.23, please try this version instead. I apologize for any frustrations from the .23 release. If you see further issues, please report them quickly and we will look into them.

ReleaseNotes1423 - memcached - Release notes for Release 1.4.23 - Memcached - Google Project Hosting for the changes new to 1.4.23, as they were significant.
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eva2000 · May 17, 2015

Code:

memcached-tool 127.0.0.1:11211 stats
#127.0.0.1:11211   Field       Value
         accepting_conns           1
               auth_cmds           0
             auth_errors           0
                   bytes      739755
              bytes_read      781144
           bytes_written     2459254
              cas_badval           0
                cas_hits           0
              cas_misses           0
               cmd_flush           0
                 cmd_get         548
                 cmd_set          93
               cmd_touch           0
             conn_yields           0
   connection_structures           7
   crawler_items_checked           0
       crawler_reclaimed           0
        curr_connections           6
              curr_items          84
               decr_hits           0
             decr_misses           0
             delete_hits           0
           delete_misses           0
       evicted_unfetched           0
               evictions           0
       expired_unfetched           0
                get_hits         476
              get_misses          72
              hash_bytes      524288
       hash_is_expanding           0
        hash_power_level          16
               incr_hits           0
             incr_misses           0
                libevent 2.0.22-stable
          limit_maxbytes   268435456
     listen_disabled_num           0
       lrutail_reflocked           0
            malloc_fails           0
                     pid        6647
            pointer_size          64
               reclaimed           0
            reserved_fds          20
           rusage_system    0.059999
             rusage_user    0.023333
   slab_reassign_running           0
             slabs_moved           0
                 threads           4
                    time  1431845817
       total_connections          23
             total_items          93
              touch_hits           0
            touch_misses           0
                  uptime          29
                 version      1.4.24

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