如何监听 MongoDB 集合的变化? [英] How to listen for changes to a MongoDB collection?

问题描述

我正在创建一种使用 MongoDB 作为数据存储的后台作业队列系统.我如何听"?在产生工作人员处理作业之前插入到 MongoDB 集合?

I'm creating a sort of background job queue system with MongoDB as the data store. How can I "listen" for inserts to a MongoDB collection before spawning workers to process the job?

我是否需要每隔几秒轮询一次以查看与上次相比是否有任何更改，或者我的脚本是否可以等待插入发生?

Do I need to poll every few seconds to see if there are any changes from last time, or is there a way my script can wait for inserts to occur?

这是我正在开发的 PHP 项目，但可以用 Ruby 或语言不可知论回答.

This is a PHP project that I am working on, but feel free to answer in Ruby or language agnostic.

推荐答案

MongoDB 有所谓的 上限集合 和 tailable cursors 允许 MongoDB 将数据推送到侦听器.

MongoDB has what is called capped collections and tailable cursors that allows MongoDB to push data to the listeners.

一个上限集合本质上是一个固定大小并且只允许插入的集合.下面是创建一个的样子:

A capped collection is essentially a collection that is a fixed size and only allows insertions. Here's what it would look like to create one:

db.createCollection("messages", { capped: true, size: 100000000 })

MongoDB Tailable 游标(Jonathan H. Wage 的原帖)

红宝石

coll = db.collection('my_collection')
cursor = Mongo::Cursor.new(coll, :tailable => true)
loop do
  if doc = cursor.next_document
    puts doc
  else
    sleep 1
  end
end

PHP

$mongo = new Mongo();
$db = $mongo->selectDB('my_db')
$coll = $db->selectCollection('my_collection');
$cursor = $coll->find()->tailable(true);
while (true) {
    if ($cursor->hasNext()) {
        $doc = $cursor->getNext();
        print_r($doc);
    } else {
        sleep(1);
    }
}

Python(由 Robert Stewart 提供)

from pymongo import Connection
import time

db = Connection().my_db
coll = db.my_collection
cursor = coll.find(tailable=True)
while cursor.alive:
    try:
        doc = cursor.next()
        print doc
    except StopIteration:
        time.sleep(1)

Perl(来自 Max)

use 5.010;

use strict;
use warnings;
use MongoDB;

my $db = MongoDB::Connection->new;
my $coll = $db->my_db->my_collection;
my $cursor = $coll->find->tailable(1);
for (;;)
{
    if (defined(my $doc = $cursor->next))
    {
        say $doc;
    }
    else
    {
        sleep 1;
    }
}

其他资源:

Ruby/Node.js 教程，带您完成创建一个应用程序来监听 MongoDB 上限集合中的插入.

一篇更详细地讨论可尾游标的文章.

使用可尾游标的 PHP、Ruby、Python 和 Perl 示例.

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