Solve two problems encountered by Redis master and slave

Recently, when I was using redis Master/Slave, I did the following two things:

1. You want to analyze redis master-slave operations. All write operations are performed on the master node, and all read operations are performed on the master node.

2 because redis is stored locally, some key read/write operations are directly put from the top.

However, the following problems occur:

1. The key of setex on the master node is always obtained from the top even after expiration.

Reproduction:

MASTER: setex abc 20 test

From:

Get abc> test

Ttl abc> 18

...

Ttl abc>-1

Get abc> test (there is still ~!)

MASTER: get abc> nil

From: get abc> nil

Therefore, if you only obtain a key from the top, you need to determine whether a key has expired Based on get + ttl.

Check the next, some people vomit this problem: http://code.google.com/p/redis/issues/detail? Id = 519

2. Perform read/write operations from the top, and the expiration time does not take effect.

Reproduction:

Redis 127.0.0.1: 6379> get abctest
(Nil)
Redis 127.0.0.1: 6379> setex abctest 20 test
OK
Redis 127.0.0.1: 6379> get abctest
"Test"
Redis 127.0.0.1: 6379> ttl abctest
(Integer) 10
Redis 127.0.0.1: 6379> ttl abctest
(Integer)-1
Redis 127.0.0.1: 6379> get abctest
"Test" (this is still available ..)

Analysis

This phenomenon is like deleting a key is never the responsibility of the master. Redis's own key deletion mechanism is

1 randomly select a certain percentage of expired keys

2. get triggers expired deletion.

Therefore, an expired key is set on the master node. If the two conditions are not triggered on the master node, the expired key will always be obtained...

This is a very easy pitfall...

Recommended reading:

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