Redis - 是否有 blpush [英] Redis - is there a blpush

问题描述

对于跨进程的数据通信，我打算使用Redis列表.生产者推送到列表，而一组消费者使用 BRPOP 消费列表内容.

For data communication across processes, I intend to use Redis list. The producer pushes to the list, while a set of consumers consume the list contents using BRPOP.

为了限制列表的大小无限增长，我想将列表大小限制为一个固定值(比如 10K 项).我很惊讶地发现没有像 BLPUSH 或 BRPUSH 这样的等效命令.这是Redis人故意省略的吗?

In order to restrict the list growing infinitely in size, I want to restrict the list size to a fixed value (say 10K items). I was surprised to find no equivalent command like BLPUSH or BRPUSH. Is this a deliberately omitted by Redis folks?

所以，我假设我必须创建一个带有 Watch/multi 的 Txn 以在推送之前检查列表大小.这是正确的方法，还是有更好的技术可用?

So, I assume I have to create a Txn with Watch/multi to check the list size before pushing. Is this the right way, or any better techniques available?

推荐答案

我会为此功能寻找 lua 脚本.

I would go for a lua script for this functionality.

LUA 接受一个键(列表名称)和两个参数，new_element_name 和 max_size.当列表已满时，返回值可以是 LPUSH 返回值或 -1.
这是执行此操作的脚本:

LUA that accepts one key (list name), and two arguments, new_element_name and max_size. Return value could be the LPUSH return value or -1 when the list is full.
Here's a script that does this:

if tonumber(ARGV[2]) > redis.call('LLEN', KEYS[1]) then
    return redis.call('LPUSH', KEYS[1], ARGV[1])  end 
return -1

您应该使用 SCRIPT LOAD 加载一次:

You should load it once with SCRIPT LOAD:

cat blpush.lua | redis-cli -x script load

并与 EVALSHA 一起使用

And use it with EVALSHA

evalsha 96d1fb35d6173758facda9dbc108296fd4a1512d 1 <myList> <new_element_name> <max_size>

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