redis is also known as caching
1.redis is a key-value storage system with no fields for ForeignKey and ManyToMany. 2. Data created in redis are not related to each other, so they are also called non-relational databases. 3. It supports the storage of data types including string, list, set, zset(sorted set -- ordered set) and hash (hash type). 4. The data types supported by redis all support push/pop, add/remove, take-intersection, merge and difference sets, and more abundant operations, and these operations are atomic. 5.redis supports sorting in various ways. To ensure efficiency, data is cached in memory. 6.redis periodically writes the updated data to disk or writes the modification operation to the additional record file, and realizes master-slave synchronization on this basis.
In a normal server, redis runs in memory, while the database runs on the server's hard disk.
Because memory runs much faster than hard disk speed, redis queries are much faster than databases stored on hard disk.
Similarly, because redis is stored in memory, a server can configure a very large hard disk. Compared with a hard disk, the configuration capacity of the server memory is much smaller than the configuration capacity of the hard disk.
So redis has some capacity limitations
Also because redis are stored in memory, the data stored in redis can easily be lost once the server is powered off.
redis stores data that is commonly used and not frequently updated
When a server comes online, when users access the data on the server, they first go to the cache to see if there is any data to query.
If the data needed by the user is stored in the cache, the data needed is obtained directly from the cache. If there is no data needed by the user in the cache, the data will be queried from the database and returned to the user. At the same time, the data will be saved in memory. In this way, when the next user accesses the same data again, he will read the required data directly from the cache instead of accessing the database, thus speeding up the user's access speed.
For example, when we publish a blog in the blog garden, the blog just published will not appear on the blog garden's home page immediately. It will take several minutes before the blog article just published appears on the blog garden's home page, which is the reason for caching.
1. Preparations
Configure epel source for CentOS system
You can refer to my blog CentOS7 System Configuration of Domestic yum Source and epel Source
2. Installing Redis
[root@bogon yum.repos.d]# yum list | grep redis Repository base is listed more than once in the configuration Repository updates is listed more than once in the configuration Repository extras is listed more than once in the configuration Repository centosplus is listed more than once in the configuration redis.x86_64 3.2.10-2.el7 @epel collectd-redis.x86_64 5.7.1-2.el7 epel collectd-write_redis.x86_64 5.7.1-2.el7 epel hiredis.x86_64 0.12.1-1.el7 epel hiredis-devel.x86_64 0.12.1-1.el7 epel opensips-redis.x86_64 1.10.5-3.el7 epel pcp-pmda-redis.x86_64 3.11.8-7.el7 base php-nrk-Predis.noarch 1.0.4-1.el7 epel php-pecl-redis.x86_64 2.2.8-1.el7 epel php-phpiredis.x86_64 1.0.0-2.el7 epel python-redis.noarch 2.10.3-1.el7 epel python-trollius-redis.noarch 0.1.4-2.el7 epel python2-django-redis.noarch 4.3.0-1.el7 epel redis-trib.noarch 3.2.10-2.el7 epel rubygem-redis.noarch 3.2.1-2.el7 epel rubygem-redis-doc.noarch 3.2.1-2.el7 epel syslog-ng-redis.x86_64 3.5.6-3.el7 epel uwsgi-logger-redis.x86_64 2.0.15-1.el7 epel uwsgi-router-redis.x86_64 2.0.15-1.el7 epel [root@bogon yum.repos.d]# yum install -y redis Loaded plugins: fastestmirror, langpacks Repository base is listed more than once in the configuration Repository updates is listed more than once in the configuration Repository extras is listed more than once in the configuration Repository centosplus is listed more than once in the configuration Loading mirror speeds from cached hostfile * epel: ftp.cuhk.edu.hk Package redis-3.2.10-2.el7.x86_64 already installed and latest version Nothing to do
3. The file directory structure of redis
Use the rpm-ql command to view the files generated in the system after redis installation
[root@bogon ~]# rpm -ql redis /etc/logrotate.d/redis /etc/redis-sentinel.conf # The daemon configuration file of redis /etc/redis.conf # redis configuration file /etc/systemd/system/redis-sentinel.service.d /etc/systemd/system/redis-sentinel.service.d/limit.conf /etc/systemd/system/redis.service.d /etc/systemd/system/redis.service.d/limit.conf /usr/bin/redis-benchmark /usr/bin/redis-check-aof /usr/bin/redis-check-rdb /usr/bin/redis-cli # redis interactive command line interface /usr/bin/redis-sentinel # The Guardian file of redis /usr/bin/redis-server # redis server-side startup file /usr/lib/systemd/system/redis-sentinel.service # Function library file of redis daemon /usr/lib/systemd/system/redis.service # redis function library file /usr/libexec/redis-shutdown # Stop redis execution file /usr/share/doc/redis-3.2.10 # redis Help File /usr/share/doc/redis-3.2.10/00-RELEASENOTES /usr/share/doc/redis-3.2.10/BUGS /usr/share/doc/redis-3.2.10/CONTRIBUTING /usr/share/doc/redis-3.2.10/MANIFESTO /usr/share/doc/redis-3.2.10/README.md /usr/share/licenses/redis-3.2.10 # licenses description of redis /usr/share/licenses/redis-3.2.10/COPYING /usr/share/man/man1/redis-benchmark.1.gz # redis man file /usr/share/man/man1/redis-check-aof.1.gz /usr/share/man/man1/redis-check-rdb.1.gz /usr/share/man/man1/redis-cli.1.gz /usr/share/man/man1/redis-sentinel.1.gz /usr/share/man/man1/redis-server.1.gz /usr/share/man/man5/redis-sentinel.conf.5.gz /usr/share/man/man5/redis.conf.5.gz /var/lib/redis # Persistent file save path of redis /var/log/redis # redis log file /var/run/redis # redis process PID file
4. Start Stop and Status View of redis
[root@bogon ~]# systemctl status redis.service # Looking at the redis status, you can see that it is active ● redis.service - Redis persistent key-value database Loaded: loaded (/usr/lib/systemd/system/redis.service; disabled; vendor preset: disabled) Drop-In: /etc/systemd/system/redis.service.d └─limit.conf Active: active (running) since Thu 2017-11-16 17:29:39 CST; 1min 44s ago Process: 6272 ExecStop=/usr/libexec/redis-shutdown (code=exited, status=0/SUCCESS) Main PID: 6286 (redis-server) CGroup: /system.slice/redis.service └─6286 /usr/bin/redis-server 0.0.0.0:6379 Nov 16 17:29:39 bogon systemd[1]: Started Redis persistent key-value database. Nov 16 17:29:39 bogon systemd[1]: Starting Redis persistent key-value database... [root@bogon ~]# systemctl stop redis.service # Stop redis [root@bogon ~]# systemctl status redis.service # The inactive state of redis ● redis.service - Redis persistent key-value database Loaded: loaded (/usr/lib/systemd/system/redis.service; disabled; vendor preset: disabled) Drop-In: /etc/systemd/system/redis.service.d └─limit.conf Active: inactive (dead) Nov 16 17:21:56 bogon systemd[1]: redis.service: control process exited, code=exited status=1 Nov 16 17:21:56 bogon systemd[1]: Unit redis.service entered failed state. Nov 16 17:21:56 bogon systemd[1]: redis.service failed. Nov 16 17:22:04 bogon systemd[1]: Started Redis persistent key-value database. Nov 16 17:22:04 bogon systemd[1]: Starting Redis persistent key-value database... Nov 16 17:29:39 bogon systemd[1]: Stopping Redis persistent key-value database... Nov 16 17:29:39 bogon systemd[1]: Started Redis persistent key-value database. Nov 16 17:29:39 bogon systemd[1]: Starting Redis persistent key-value database... Nov 16 17:31:38 bogon systemd[1]: Stopping Redis persistent key-value database... Nov 16 17:31:38 bogon systemd[1]: Stopped Redis persistent key-value database. [root@bogon yum.repos.d]# redis-server # Start redis program 5587:C 16 Nov 15:42:56.010 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf 5587:M 16 Nov 15:42:56.018 * Increased maximum number of open files to 10032 (it was originally set to 1024). _._ _.-``__ ''-._ _.-`` `. `_. ''-._ Redis 3.2.10 (00000000/0) 64 bit .-`` .-```. ```\/ _.,_ ''-._ ( ' , .-` | `, ) Running in standalone mode |`-._`-...-` __...-.``-._|'` _.-'| Port: 6379 | `-._ `._ / _.-' | PID: 6519 `-._ `-._ `-./ _.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | http://redis.io `-._ `-._`-.__.-'_.-' _.-' |`-._`-._ `-.__.-' _.-'_.-'| | `-._`-._ _.-'_.-' | `-._ `-._`-.__.-'_.-' _.-' `-._ `-.__.-' _.-' `-._ _.-' `-.__.-' 5587:M 16 Nov 15:42:56.022 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128. 5587:M 16 Nov 15:42:56.022 # Server started, Redis version 3.2.10 5587:M 16 Nov 15:42:56.022 # WARNING overcommit_memory is set to 0! Background save may fail under low memory condition. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect. 5587:M 16 Nov 15:42:56.025 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled. 5587:M 16 Nov 15:42:56.026 * The server is now ready to accept connections on port 6379 [root@bogon ~]# systemctl status redis.service ● redis.service - Redis persistent key-value database Loaded: loaded (/usr/lib/systemd/system/redis.service; disabled; vendor preset: disabled) Drop-In: /etc/systemd/system/redis.service.d └─limit.conf Active: active (running) since Thu 2017-11-16 17:31:47 CST; 2s ago Main PID: 6325 (redis-server) CGroup: /system.slice/redis.service └─6325 /usr/bin/redis-server 0.0.0.0:6379 Nov 16 17:31:47 bogon systemd[1]: Started Redis persistent key-value database. Nov 16 17:31:47 bogon systemd[1]: Starting Redis persistent key-value database...
There are two ways to start redis:
[root@bogon ~]# systemctl start redis.service # Background boot, no welcome interface [root@bogon ~]# redis-server # Front-end boot, you can see the welcome interface
There are two ways to stop redis:
[root@bogon ~]# systemctl stop redis.service [root@bogon ~]# /usr/libexec/redis-shutdown
5. Description of redis master configuration file
bind 127.0.0.1 # redis-bound host address, which by default only supports local connections protected-mode yes # Whether to run redis in protected mode port 6379 # Specify the port redis listens on tcp-backlog 511 timeout 0 # How long does the client remain idle and close the connection at 0:00? tcp-keepalive 300 # Maximum number of connections allowed in tcp mode daemonize no # Is it running as a daemon supervised no # Do not use monitoring trees pidfile /var/run/redis_6379.pid # The redis runtime saves pid files loglevel verbose # Log file recording mode, default to standard output logfile /var/log/redis/redis.log # Save path of redis log file databases 16 # Number of redis databases in the system save 900 1 # When there is an update operation in 900 seconds in redis, the data is synchronized to the file and saved. save 300 10 # When redis has 10 update operations in 300 seconds, it synchronizes the data to a file to save. save 60 10000 # When redis has 10,000 updates in 60 seconds, it synchronizes the data to a file for storage. stop-writes-on-bgsave-error yes rdbcompression yes # Whether to start compression when data in redis is saved to local database by default yes rdbchecksum yes dbfilename dump.rdb # File name of local database dir /var/lib/redis # Path of local database slave-serve-stale-data yes slave-read-only yes repl-diskless-sync no repl-diskless-sync-delay 5 repl-disable-tcp-nodelay no slave-priority 100 appendonly no # Whether to log every update operation appendfilename "appendonly.aof" # Specify the file name for the update log appendfsync everysec # Synchronize data in redis to local files once a second no-appendfsync-on-rewrite no auto-aof-rewrite-percentage 100 auto-aof-rewrite-min-size 64mb aof-load-truncated yes lua-time-limit 5000 slowlog-log-slower-than 10000 slowlog-max-len 128 latency-monitor-threshold 0 notify-keyspace-events "" hash-max-ziplist-entries 512 hash-max-ziplist-value 64 list-max-ziplist-size -2 list-compress-depth 0 set-max-intset-entries 512 zset-max-ziplist-entries 128 zset-max-ziplist-value 64 hll-sparse-max-bytes 3000 activerehashing yes client-output-buffer-limit normal 0 0 0 client-output-buffer-limit slave 256mb 64mb 60 # client-output-buffer-limit pubsub 32mb 8mb 60 hz 10 aof-rewrite-incremental-fsync yes
6.redis interactive interface
[root@bogon ~]# redis-cli # Interactive interface into redis 127.0.0.1:6379>
As you can see, we have entered the interactive environment of redis.
127.0.0.1:6379> set k1 v1 # Set the value of k1 to v1 OK 127.0.0.1:6379> get k1 # Get the value of k1 "v1" 127.0.0.1:6379> set k2 v2 # Set the value of k2 to v2 OK 127.0.0.1:6379> get k2 # Get the value of k2 "v2"
7. Python 3 operation redis
Open redis configuration file / etc/redis.conf in linux system
Amend line 61 to read
bind 0.0.0.0
Represents that all hosts can be connected
Then restart redis to make the configuration file effective
[root@bogon ~]# systemctl restart redis.service
Install redis module in windows system
pip3 install redis
Create a new redis_test.py file with the contents of
import redis
r1=redis.Redis(host="192.168.16.220",port=6379)
print("k1 value read for the first time:", "r1.get("k1")))
print("k2 value read for the first time:", "r1.get("k2")))
r1.set("k3","v3")
r1.delete("k1")
r1.delete("k2")
print("Get the value of K1 for the second time", r1.get("k1")
print("Get the value of K2 for the second time", r1.get("k2")
print(r1.get("k3"))Operation results:
k1 value read for the first time: b'v1' k2 value read for the first time: b'v2' Get the value of k1 for the second time None The second acquisition of the value of k2 None b'v3'
Get the values of k1 and k2 again at the command prompt of linux
127.0.0.1:6379> get k1 (nil) 127.0.0.1:6379> get k2 (nil)
Because the values of k1 and k2 have been deleted in redis_test.py, the value obtained is None.
8. Benefits of Redis
(1) Fast speed, because data exists in memory, similar to HashMap, HashMap has the advantage that the time complexity of search and operation is O(1) (2) Support rich data types, string, list, set, sorted set, hash (3) Supporting transactions, operations are atomic, so-called atomicity is the change of data or all of them are executed, or none of them are executed. (4) Rich features: can be used for caching, messages, set expiration time by key, after expiration will be automatically deleted