内存缓存Memcached 1.4.18发布。2014-04-18 上一个版本是2013-12-22的1.4.17 此版本新特性包括stats conns命令可以显示打开和空闲的连接，启动时指定hash算法如-o hash_algorithm=murmur3，lru_crawler以及一些Bug修正。
fix LRU contention for first minute of uptime
This made some synthetic benchmarks look awful.
Make hash table algorithm selectable
Don't lose item_size_max units in command line
Add a "stats conns" command to show the states of open connections.
Allow caller-specific error text in binary protocol
Stop returning ASCII error messages to binary clients
Fix reference leak in binary protocol "get" and "touch" handlers
Fix reference leak in process_get_command()
New "stats conns" command, which will show you what currently open connections are up to, how idle they've been, etc.
Starttime Hash Algorithm Selection
The jenkins hash was getting a little long in the tooth, and we might want to add specific hash algorithms for different platforms in the future. This makes it selectable in some sense. We've initially added murmur3 hash to the lineup and that seems to run a tiny bit faster in some tests.
A new background thread emerges! Currently experimental, so the syntax might change. If you run into bugs please let us know (though it's been testing fine in torture tests so far).
If you wish to clean your slab classes of items which have been expired, either one-time or periodically, this will do it with low impact as a background operation.
Currently it requires kicking off a crawl via manual command:
First, enable the thread:lru_crawler enableor use-o lru_crawleras a starttime option.
lru_crawler crawl 1,3,5
... would crawl slab classes 1,3,5 looking for expired items to add to the freelist.
This is generally not useful or required, unless you have memory with very mixed TTLs, you do not fetch items frequently enough or otherwise cause them to expire, and you don't want items with longer TTLs block reclaiming expired items, or to be evicted early.
Future uses of the thread should allow examining and purging items via a plugin interface: IE crawl all items matching some string and remove them, or count them. It is simple to modify to experiment with as of now.
See doc/protocol.txt for full explanation of related commands and counters.