如何使用rdbtools分析redis大key

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于航

修改于 2021-03-19 03:39:15

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文章被收录于专栏：腾讯云数据库专家服务腾讯云数据库专家服务

大key的危害

熟悉redis的朋友都知道，大key是在应用的设计和实践当中应该尽量避免的风险。大key的危险有很多，例如：

导致流量达到瓶颈
造成分片容量的倾斜
更严重的是读写大key导致系统无响应，产生大量慢查询等等

一般我们认为超过10kb大小的string类型的key或者超过1万个元素的set可以称为大key，应该进行合理的拆分

大key的获取

如何获取大key对于使用云数据库的朋友们来说，是比较轻松的一件事情，因为很多云厂商都默认提供了大key的分析工具，例如腾讯云数据库在【控制台】【系统监控】【监控概览】页面提供了大key分析功能，其原理是分析静态RDB文件然后从中抓出大key按照大小顺序排序，本文的重点是分享下如何使用开源工具rdbtools进行大key分析

rdbtools的安装

rdbtools有三个主要的功能

分析静态rdb文件并生成csv格式的内存报告
将rdb文件转储成为json格式
利用diff工具比较两个rdb文件的不同下面我们开始

1.第一步我们先安装python和pip

由于作者操作系统使用的是centos8.0，默认提供了python3和pip3因此无需额外安装，读者可以自行安装，网上教程很多，不再赘述。

>>> import sys
>>> sys.version
'3.6.8 (default, May 21 2019, 23:51:36) \n[GCC 8.2.1 20180905 (Red Hat 8.2.1-3)]'
>>>

2.获取rdb文件

自建redis的同学可以使用redis-port工具集导出rdb文件。使用云数据库的朋友可以联系云厂商获取下载链接。

直接导出到本地或者使用rz/sz导入到自己的机器中

[root@VM-4-10-centos ~]# yum install lrzsz
Last metadata expiration check: 0:10:21 ago on Thu 18 Mar 2021 04:31:25 PM CST.
Dependencies resolved.
========================================================================================================================================================================================
 Package                                  Arch                                      Version                                             Repository                                 Size
========================================================================================================================================================================================
Installing:
 lrzsz                                    x86_64                                    0.12.20-43.el8                                      BaseOS                                     84 k

Transaction Summary
========================================================================================================================================================================================
Install  1 Package

Total download size: 84 k
Installed size: 190 k
Is this ok [y/N]: y
Downloading Packages:
lrzsz-0.12.20-43.el8.x86_64.rpm                                                                                                                         2.2 MB/s |  84 kB     00:00    
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total                                                                                                                                                   2.1 MB/s |  84 kB     00:00     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Preparing        :                                                                                                                                                                1/1 
  Installing       : lrzsz-0.12.20-43.el8.x86_64                                                                                                                                    1/1 
  Running scriptlet: lrzsz-0.12.20-43.el8.x86_64                                                                                                                                    1/1 
  Verifying        : lrzsz-0.12.20-43.el8.x86_64                                                                                                                                    1/1 

Installed:
  lrzsz-0.12.20-43.el8.x86_64                                                                                                                                                           

Complete!

3.安装rdbtools

[root@VM-4-10-centos ~]# pip install rdbtools

安装好之后通过help命令简单了解下，注意--command or -c是必选参数

[root@VM-4-10-centos ~]# rdb --help
usage: usage: rdb [options] /path/to/dump.rdb

Example : rdb --command json -k "user.*" /var/redis/6379/dump.rdb //表示从dump.rdb文件中分析出所有以`user.`开头的key并输出为jason格式，打印到屏幕上

positional arguments: //位置参数
  dump_file             RDB Dump file to process

optional arguments:
  -h, --help            show this help message and exit//查看命令的帮助信息
  -c CMD, --command CMD//必选参数，-c json表示存储成json格式，最常用的是 -c memory表示生成csv格式的内存快照，还有diff模式进行对比
                        Command to execute. Valid commands are json, diff,
                        justkeys, justkeyvals, memory and protocol
  -f FILE, --file FILE  //输出到文件
                        Output file
  -n DBS, --db DBS      //指定只分析某个编号的db，例如db0，如果不指定默认包含所有
                        Database Number. Multiple databases can be provided.
                        If not specified, all databases will be included.
  -k KEYS, --key KEYS   //指定分析并导出某个前缀的key，支持正则表达式
                        Keys to export. This can be a regular expression
  -o NOT_KEYS, --not-key NOT_KEYS //指定不分析并导出某个前缀的key，支持正则表达式
                        Keys Not to export. This can be a regular expression
  -t TYPES, --type TYPES //指定分析哪些数据类型，例如string、hash、set、list、sortedset等，可以指定多个类型，如果不指定默认分析所有
                        Data types to include. Possible values are string,
                        hash, set, sortedset, list. Multiple typees can be
                        provided. If not specified, all data types will be
                        returned
  -b BYTES, --bytes BYTES //指定输出超过多少Byte的key，例如--bytes 10240表示只输出超过10k大小的key
                        Limit memory output to keys greater to or equal to
                        this value (in bytes)
  -l LARGEST, --largest LARGEST //输出TOP多少的key，例如--largest 100，表示只输出top 100的key
                        Limit memory output to only the top N keys (by size)
  -e {raw,print,utf8,base64}, --escape {raw,print,utf8,base64} //指定输出的默认编码，默认RAW
                        Escape strings to encoding: raw (default), print,
                        utf8, or base64.
  -x, --no-expire       With protocol command, remove expiry from all keys // 只有command为protocol模式才有效，表示不输出所有的可过期的key，只输出哪些永不过期的key
  -a N, --amend-expire N // 只有command为protocol模式才有效，表示给设置过期时间的key增加N秒的过期时间
                        With protocol command, add N seconds to key expiry
                        time

4.接下来我们简单分析下

[root@VM-4-10-centos ~]# rdb --command json dump.rdb > ./test
WARNING: python-lzf package NOT detected. Parsing dump file will be very slow unless you install it. To install, run the following command:

pip install python-lzf

这里提示我们由于没有python-lzf包导致分析速度很慢，那我们就安装一下吧。可以先更新一下yum源，防止找不到包

[root@VM-4-10-centos ~]# yum update

然后再次安装

[root@VM-4-10-centos ~]# pip install python-lzf
WARNING: Running pip install with root privileges is generally not a good idea. Try `pip install --user` instead.
Collecting python-lzf
  Downloading http://mirrors.tencentyun.com/pypi/packages/e3/33/b8f67bbe695ccc39f868ae55378993a7bde1357a0567803a80467c8ce1a4/python-lzf-0.2.4.tar.gz
Installing collected packages: python-lzf
  Running setup.py install for python-lzf ... error
    Complete output from command /usr/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-go178sdk/python-lzf/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-6oauj90r-record/install-record.txt --single-version-externally-managed --compile:
    running install
    running build
    running build_ext
    building 'lzf' extension
    creating build
    creating build/temp.linux-x86_64-3.6
    gcc -pthread -Wno-unused-result -Wsign-compare -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I. -I/usr/include/python3.6m -c lzf_module.c -o build/temp.linux-x86_64-3.6/lzf_module.o -Wall
    gcc: error: /usr/lib/rpm/redhat/redhat-hardened-cc1: No such file or directory
    error: command 'gcc' failed with exit status 1
    
    ----------------------------------------
Command "/usr/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-go178sdk/python-lzf/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-6oauj90r-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-go178sdk/python-lzf/

这里报错gcc编译的时候报错了，上github搜索了一下，是没有安装 redhat-rpm-config，那我们就安装下

$ sudo dnf install redhat-rpm-config

安装好redhat-rpm-config之后，再安装python-lzf又报错了，这次提示少了Python.h，上网查了下，原来这次是缺乏python-devel。

[root@VM-4-10-centos ~]# pip install python-lzf
WARNING: Running pip install with root privileges is generally not a good idea. Try `pip install --user` instead.
Collecting python-lzf
  Downloading http://mirrors.tencentyun.com/pypi/packages/e3/33/b8f67bbe695ccc39f868ae55378993a7bde1357a0567803a80467c8ce1a4/python-lzf-0.2.4.tar.gz
Installing collected packages: python-lzf
  Running setup.py install for python-lzf ... error
    Complete output from command /usr/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-dxcuwlzv/python-lzf/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-9n6nf8r_-record/install-record.txt --single-version-externally-managed --compile:
    running install
    running build
    running build_ext
    building 'lzf' extension
    creating build
    creating build/temp.linux-x86_64-3.6
    gcc -pthread -Wno-unused-result -Wsign-compare -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -D_GNU_SOURCE -fPIC -fwrapv -fPIC -I. -I/usr/include/python3.6m -c lzf_module.c -o build/temp.linux-x86_64-3.6/lzf_module.o -Wall
    lzf_module.c:3:10: fatal error: Python.h: No such file or directory
     #include "Python.h"
              ^~~~~~~~~~
    compilation terminated.
    error: command 'gcc' failed with exit status 1
    
    ----------------------------------------
Command "/usr/bin/python3.6 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-dxcuwlzv/python-lzf/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-9n6nf8r_-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-build-dxcuwlzv/python-lzf/

我们直接yum安装可以找不到，例如下面所示，我们尝试搜索一下yum search一下，找到了，python36-devel.x86_64,然后再次安装。

[root@VM-4-10-centos ~]# yum install python-devel
Last metadata expiration check: 0:00:58 ago on Thu 18 Mar 2021 05:14:53 PM CST.
No match for argument: python-devel
Error: Unable to find a match: python-devel

[root@VM-4-10-centos ~]# yum search python3 | grep devel
Last metadata expiration check: 0:01:29 ago on Thu 18 Mar 2021 05:14:53 PM CST.
python3-qscintilla-qt5-devel.noarch : Development files for QScintilla-qt5 python3 bindings
boost169-mpich-python3-devel.x86_64 : Shared library symbolic links for Boost.MPI Python 3 component
boost169-openmpi-python3-devel.x86_64 : Shared library symbolic links for Boost.MPI Python 3 component
boost169-python3-devel.x86_64 : Shared object symbolic links for Boost.Python 3
python3-TurboGears2.noarch : Next generation front-to-back web development megaframework
python3-cherrypy.noarch : Pythonic, object-oriented web development framework
python3-hupper.noarch : Integrated process monitor for developing servers
python3-idle.i686 : A basic graphical development environment for Python
python3-idle.x86_64 : A basic graphical development environment for Python
python3-kobo.noarch : Python modules for tools development
python3-pycxx-devel.noarch : PyCXX header and source files
python3-werkzeug.noarch : The Swiss Army knife of Python web development
python36-devel.x86_64 : Libraries and header files needed for Python development
python38-devel.x86_64 : Libraries and header files needed for Python development
python38-idle.x86_64 : A basic graphical development environment for Python

搞定了这些依赖，我们再次安装就很顺利了

[root@VM-4-10-centos ~]# pip install python-lzf
WARNING: Running pip install with root privileges is generally not a good idea. Try `pip install --user` instead.
Collecting python-lzf
  Downloading http://mirrors.tencentyun.com/pypi/packages/e3/33/b8f67bbe695ccc39f868ae55378993a7bde1357a0567803a80467c8ce1a4/python-lzf-0.2.4.tar.gz
Installing collected packages: python-lzf
  Running setup.py install for python-lzf ... done
Successfully installed python-lzf-0.2.4

5.正式分析

接下来给一个常用的命令，分析rdb文件当中top100的大key，可以使用lrzsz下载到本地，使用Excel进行分析。

root@VM-4-10-centos ~]# rdb -c memory dump-6120957-redis-server-ignore-140016731-ignore-1-ignore.rdb -l 100  -f ./dump_memory.csv

CSV中字段说明

database	type	key	size_in_bytes	encoding	num_elements	len_largest_element	expiry
key所属db编号	key的类型例如string list set等	key名	key大小(字节数)	编码方式(hashtable，ziplist，string等)	key中元素的个数	key中最大元素的长度	过期时间