INCR和DECR是Redis中用於原子性增減數(shù)值的命令。 1. INCR命令將鍵的值加1，若鍵不存在則創(chuàng)建並設(shè)為1，若存在且為整數(shù)則遞增，否則返回錯(cuò)誤；2. DECR命令將鍵的值減1，邏輯類似，適用於庫存管理或餘額控制等場(chǎng)景；3. 兩者僅適用於可解析為整數(shù)的字符串類型，操作前需確保數(shù)據(jù)類型正確；4. 常用於並發(fā)場(chǎng)景如API限流、事件計(jì)數(shù)及分佈式系統(tǒng)中的共享計(jì)數(shù)，並可結(jié)合EXPIRE實(shí)現(xiàn)自動(dòng)重置的臨時(shí)計(jì)數(shù)器。

When you're working with Redis, atomic increment and decrement operations are handled cleanly using the INCR and DECR commands. These are simple but powerful tools for safely updating numeric values stored under a key, without worrying about race conditions.

Using INCR to Atomically Increment a Value

The INCR command increases the value of a key by 1. It's atomic, meaning even if multiple clients try to increment the same key at once, Redis ensures each operation is completed one after another, avoiding conflicts.

• If the key doesn't exist, Redis creates it and sets its value to 1.
• If the key exists and holds a string that can be interpreted as an integer, Redis increments it.
• If the stored value isn't a valid integer, Redis returns an error.

Example:

 > SET counter 10
OK
> INCR counter
(integer) 11

This is commonly used for things like tracking page views, login counts, or API rate limiting.

Using DECR to Atomically Decrement a Value

Just like INCR , the DECR command decreases the value of a key by 1 in a thread-safe way.

• If the key doesn't exist, Redis creates it and sets its value to -1.
• If the key contains a valid integer, Redis decrements it.
• As with INCR , invalid data types will cause Redis to return an error.

Example:

 > SET counter 10
OK
> DECR counter
(integer) 9

A common use case might be managing inventory levels or handling token balances where real-time accuracy matters.

Handling Edge Cases and Data Types

Both INCR and DECR work only with string keys that represent integers. You'll run into issues if you try to use them on other data types like lists or hashes.

If you're not sure what kind of data is stored under a key, check it first using GET or wrap your logic in code that handles type errors gracefully.

Here are some gotchas:

• Redis strings have a size limit of 512MB, but when used as integers, they must fit within 64-bit signed integer ranges.
• Always validate input before passing it to INCR or DECR from user input or external sources.

When to Use These Commands in Real Applications

These commands shine in scenarios where concurrency matters — for example:

• Rate limiting (eg, track how many times a user hits an API endpoint)
• Counting events (like likes, comments, or page visits)
• Managing shared counters across distributed systems

They eliminate the need for locking mechanisms because Redis handles synchronization internally.

You can also combine these commands with Redis' expiration system ( EXPIRE ) for temporary counters that reset automatically after a time window.

基本上就這些。 Redis 的INCR和DECR命令簡(jiǎn)單但實(shí)用，用好了能省不少並發(fā)處理的麻煩。

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