Introduction of Redis expiration mechanism

Overview

In the actual development process will often encounter some time-sensitive data, such as limited time discount activities, caching or verification code, and so on. After a while, you need to delete this data. In a relational database, you typically add a field to record the expiration time of the data, and then periodically check for expired data and then delete it. Redis itself provides a good support for key expiration. Redis expiration mechanism

In Redis you can use the EXPIRE command to set the lifetime of a key (Ttl:time to live), over which time the key is automatically deleted, and the EXPIRE command is used as follows:

1	EXPIRE key TTL (per second)

A command return of 1 indicates that the TTL was set successfully, and 0 indicates that the key does not exist or the setting fails.

As an example:

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127.0.0.1:6379> Set session + OK 127.0.0.1:6379> EXPIRE session 5 (integer) # 1 127.0.0.1:6379> get session "127.0.0.1:6379>" 127.0.0.1:6379> Get session (nil) 127.0.0.1:6379>

The previous example shows that the value of the session is set to 100, and then set his TTL to 5s, and after several successive use of the GET command to obtain session,5s will not get a session, because the TTL time has arrived, the session is deleted.

If you want to know how long a key has been deleted, you can use the TTL command to view it, using the following methods:

1

TTL Key

The return value is the time remaining in the key, in seconds.

Like what:

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127.0.0.1:6379> Set session + OK 127.0.0.1:6379> EXPIRE session (integer) # 1 127.0.0.1:6379> TTL session (in Teger) 7 127.0.0.1:6379> ttl session (integer) 5 127.0.0.1:6379> ttl session (integer) 2 127.0.0.1:6379> ttl sess Ion (integer) 0 127.0.0.1:6379> ttl session (integer)-2 127.0.0.1:6379> ttl session (integer)-2 127.0.0.1:6379>

Visible, the return value of the TTL will slowly decrease over time, the key will be deleted after 10s, the TTL will return when the key does not exist-2, and when no expiration time is set for the key, the remaining time to use the TTL fetch key will return-1, for example

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127.0.0.1:6379> set URL http://qifuguang.me OK 127.0.0.1:6379> ttl url (integer)-1 127.0.0.1:6379>

If you want to cancel the expiration time of a key, you can use the PERSIST command as follows:

1	PERSIST Key

The purge successfully returns 1, and the failure returns 0.

For example:

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127.0.0.1:6379> set title winwill2012 OK 127.0.0.1:6379> EXPIRE title (integer) 1 127.0.0.1:6379> TTL title (integer) 127.0.0.1:6379> PERSIST title (integer) 1 127.0.0.1:6379> TTL title (integer)-1 127.0.0.1:6379>

In addition to the persist command clears the expiration of the key, the Set,getset command clears the expiration of the key, but commands that operate on the key (such as Incr,lpush, and so on) do not erase the expiration of the key.

the unit of the expire command is seconds, and if you want more accurate expiration time, you can use the Pexpire command, which is in milliseconds, and you can use Pttl to see the remaining time accordingly.

if the watch command monitors a key that has an expiration time, if the key expires automatically during monitoring, watch does not think the key is changed use of the Redis expiration mechanism

With the expiration mechanism can achieve a lot of time-related functions, such as access frequency restrictions, as a cache, and so on, the specific details will not unfold, there are questions can leave a message. Statement

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