AI导航网
微信公众号搜"智元新知"关注
微信扫一扫可直接关注哦！

How-to Dump Keys from Memcache--reference

分类：Memcache作者：编程之家

<div class="Meta">
<div class="submitted">Submitted by lars Windolf on 19. October 2012 - 21:53


<div class="submitted">http://lzone.de/dump%20memcache%20keys

You spent already 50GB on the memcache cluster,but you still see many evictions and the cache hit ratio doesn't look good since a few days. The developers swear that they didn't change the caching recently,they checked the code twice and have found no problem.

What Now? How to get some insight into the black Box of memcached? One way would be to add logging to the application to see and count what is being read and written and then to guess from this about the cache efficiency. For to debug what's happening we need to set how the cache keys are used by the application.

An Easier Way

Memcache itself provides a means to peek into its content. The memcache protocol provides to peek into the data that is organized by slabs (categories of data of a given size range). There are some significant limitations though:

  1. You can only dump keys per slab class (keys with roughly the same content size)
  2. You can only dump one page per slab class (1MB of data)
  3. This is an unofficial feature that

The second limitation is propably the hardest because 1MB of several gigabytes is almost nothing. Still it can be useful to watch how you use a subset of your keys. But this might depend on your use case.

If you don't care about the technical details just skip to the to learn about what tools allow you to easily dump everything. Alternatively follow the following guide and try the commands against your memcached setup.

How it Works

First you need to kNow how memcache organizes its memory. If you start memcache with option "-vv" you see the slab classes it creates. For example

$ memcached -vv
slab class   1: chunk size        96 perslab   10922
slab class   2: chunk size       120 perslab    8738
slab class   3: chunk size       152 perslab    6898
slab class   4: chunk size       192 perslab    5461
[...]
@H_502_21@

In the configuration printed above memcache will keep fit 6898 pieces of data between 121 and 152 byte in a single slab of 1MB size (6898*152). All slabs are sized as 1MB per default. Use the following command to print all currently existing slabs:


stats slabs@H_502_21@

If you've added a single key to an empty memcached 1.4.13 with


set mykey 0 60 1
1
STORED
@H_502_21@

you'll Now see the following result for the "stats slabs" command:


stats slabs
STAT 1:chunk_size 96
STAT 1:chunks_per_page 10922
STAT 1:total_pages 1
STAT 1:total_chunks 10922
STAT 1:used_chunks 1
STAT 1:free_chunks 0
STAT 1:free_chunks_end 10921
STAT 1:mem_requested 71
STAT 1:get_hits 0
STAT 1:cmd_set 2
STAT 1:delete_hits 0
STAT 1:incr_hits 0
STAT 1:decr_hits 0
STAT 1:cas_hits 0
STAT 1:cas_badval 0
STAT 1:touch_hits 0
STAT active_slabs 1
STAT total_malloced 1048512
END
@H_502_21@

The example shows that we have only one active slab type #1. Our key being just one byte large fits into this as the smallest possible chunk size. The slab statistics show that currently on one page of the slab class exists and that only one chunk is used.


Most importantly it shows a counter for each write operation (set,incr,decr,cas,touch) and one for gets. Using those you can determine a hit ratio!


You can also fetch another set of infos using "stats items" with interesting counters concerning evictions and out of memory counters.


stats items
STAT items:1:number 1
STAT items:1:age 4
STAT items:1:evicted 0
STAT items:1:evicted_nonzero 0
STAT items:1:evicted_time 0
STAT items:1:outofmemory 0
STAT items:1:tailrepairs 0
STAT items:1:reclaimed 0
STAT items:1:expired_unfetched 0
STAT items:1:evicted_unfetched 0
END
@H_502_21@

What We Can Guess Already...


Given the statistics infos per slabs class we can already guess a lot of thing about the application behavIoUr:


    

  1. How is the cache ratio for different content sizes?

      

    • How good is the caching of large HTML chunks?
      • 

    

    2. 

  2. How much memory do we spend on different content sizes?

      

    • How much do we spend on simple numeric counters?
      • 

    • How much do we spend on our session data?
      • 

    • How much do we spend on large HTML chunks?
      • 

    

    3. 

  3. How many large objects can we cache at all?
    4. 



Of course to answer the questions you need to kNow about the cache objects of your application.


Now: How to Dump Keys?


Keys can be dumped per slabs class using the "stats cachedump" command.


stats cachedump  @H_502_21@

To dump our single key in class #1 run


stats cachedump 1 1000
ITEM mykey [1 b; 1350677968 s]
END
@H_502_21@

The "cachedump" returns one item per line. The first number in the braces gives the size in bytes,the second the timestamp of the creation. Given the key name you can Now also dump its value using


get mykey
VALUE mykey 0 1
1
END
@H_502_21@

This is it: iterate over all slabs classes you want,extract the key names and if need dump there contents.


Dumping Tools


There are different dumping tools sometimes just scripts out there that help you with printing memcache keys:

PHP
libmemcachedweaver.com/2009/04/20/peeping-into-memcached/">peepDoes freeze your memcached process!!!


Be careful when using this in production. But can thereby workaround the 1MB limitation and really dump all keys.


                
                                 
版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 [email protected] 举报，一经查实，本站将立刻删除。

                            
                    
                
                

                    

                        

                            
相关推荐

                            

                                 
缓存穿透，缓存雪崩的四种解决方案

                                
前言设计一个缓存系统，不得不要考虑的问题就是：缓存穿透、缓存击穿与失效时的雪崩效应。缓存穿透缓存穿透是指查询一个一定不存在的数据，由于缓存是不命中时被动写的，并且出于容错考虑，如果从存储层查不到数据则...

                  
                                
                            

                                 
Memcache安装

                                
在192.168.80.100要联网关闭防火墙及SElinuxsystemctlstopfirewalld//关闭防火墙setenforce0//关闭监控memcached服务器：上传源码包和插件包：yuminstalllrz*-y把memcached-1.5.6.tar.gzlibevent-2.1.8-stable.tar.g...

                  
                                
                            

                                 
redis -memcahe

                                
Redis与Memcache对比：1.Memcache是一个分布式的内存对象缓存系统而redis是可以实现持久存储2.Memcache是一个LRU的缓存redis支持更多的数据类型3.Memcache是多线程的redis是单线程的4.二者性能几乎不相上下，实际上r...

                  
                                
                            

                                 
Mencache安装及实验

                                
安装Mencache：关闭防火墙及SElinuxsystemctl  stop  firewalldsetenforce  0memcached服务器：上传源码包和插件包：yum install  lrz*  -ymemcached-1.5.9.tar.gzlibevent-2.1.8-stable.tar.gz解压tarxf...

                  
                                
                            

                                 
php安装yaf，memcache，memcached模块

                                
#安装php的yaf模块，参考https://www.cnblogs.com/shifu204/p/6743578.htmlhttps://www.cnblogs.com/jiqing9006/p/9646872.htmlCentOS用phpize安装PHP扩展出现Can'tfindPHPheadersin/usr/include/php原因：http...

                  
                                
                            

                                 
windows下安装配置apache、php、mysql、redis、memcache

                                
win10下安装配置apache、php、mysql、redis、memcache资源官网下载亲测可用。名称版本下载地址网盘提取码apache2.4.38-x64下载地址33h4mysql5.5.62下载地址zicrphp7.1.26-ts-x64下载地址6ar6redis4.0.2.3-x64下载地址...

                  
                                
                            

                                 
php5.4之分布式缓存memcachewindows7下安装配置

                                
使用理由：就是为了频繁查询数据库。并且数据有多！那么存到memcached内存就能够避免数据库的不断被訪问，从而提速一、安装memcachememcached在windows7上的安装问题 如今安装包：http://download.csdn.net/detail/...

                  
                                
                            

                                 
Memcache 和 Redis

                                
https://www.cnblogs.com/xrq730/p/4948707.htmlMemCache是什么理解memcached的内存存储机制SlabAllocator内存分配机制Memcached默认情况下采用了名为SlabAllocator的机制分配、管理内存。0.之前内存分配的弊端在该机...

                  
                                
                            

                                 
Memcache内存对象缓存框架

                                
 转载请注明原文地址：https://www.cnblogs.com/ygj0930/p/10923221.html 一：Memcache是什么，为什么要用它 二：Memcache指令有哪些 三：Memcache使用实例 四：Memcache深入解读

                  
                                
                            

                                 
memcache讲解和在.net中初使用

                                
memcache讲解和在.net中初使用2017年10月17日22:51:36 等待临界 阅读数：503  前言传统数据库面临的问题数据库死锁磁盘IO正文了解memcache原理基本命令memcache与memcachedmemcache的适用范围memcache的客户端和...

                  
                                
                            

                    



            
            

              
          

            

              




              

            

          

          
           
          

            

              

                
    
              
    
            
    
          
    
          
          
          
    
            
    
              
    
                
                
    pythonJavaScriptjavaHTMLreactjsC#AndroidCSSNode.jssqlrpython-3.xMysqLjQueryc++pandasFlutterangularIOSdjangolinuxswifttypescript路由器JSON路由器设置无线路由器h3c华三华三路由器设置华三路由器电脑软件教程arraysdocker软件图文教程Cvue.jslaravelspring-bootreact-native