Java App Engine - 排名计数器

发布于 2024-08-25 23:00:13 字数 479 浏览 8 评论 0原文

我了解分片计数器，如下：http://code.google.com/appengine/ articles/sharding_counters.html 问题是简单的计数器在我的应用程序中不起作用。我按特定变量对实体进行排序，因此返回的不是计数，而是排名。我当前的方法是：

SELECT COUNT(this) FROM Entity.class WHERE value <= ?

结果+1是参数相对于持久实体对象中的值变量的排名。这样做的限制是返回的最高排名是 1001，因为 count() 最多可以给出 1000。我无法在实体对象上存储排名的原因是排名经常更新，重新设置此排名变量的成本太高。

关于实现这一目标的最佳方法有什么想法吗？

原文

I understand the sharded counter, here: http://code.google.com/appengine/articles/sharding_counters.html The problem is that a simple counter will not work in my application. I am sorting my entities by a particular variable so I am returned not so much a count, but more of a rank. My current method is:

SELECT COUNT(this) FROM Entity.class WHERE value <= ?

Result + 1 is then the rank of the parameter in relation to the value variable in the persistent Entity objects. The limitation of this is the highest rank being returned is 1001 because count() can give a maximum of 1000.
The reason I cannot store the rank on the Entity object is that the ranks are updated very often, and re-setting this rank variable would be much too costly.

Any ideas on the best way to accomplish this?

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甜扑 2024-09-01 23:00:13

您可能需要考虑调整 google-appengine-ranklist 项目到 Java。它构建了一个“ranker”节点树，这样可以在 O(log n) 时间内找到第 n 个排名项，并且更新同样为 O(log n)。

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尘世孤行 2024-09-01 23:00:13

我将创建一个带有静态变量的类来保存当前计数值。例如，您可以创建如下内容：

public class Counter {
    private static int counter = -1;

    public static synchronized int getNextValue() {
    if (counter == -1) {                
            counter = // Insert code that retrieves the highest value from Google datastore
    }
    counter++;
    return counter;
    }
}

I would create a class with a static variable to hold the current count value. E.g., you could create something like the following:

public class Counter {
    private static int counter = -1;

    public static synchronized int getNextValue() {
    if (counter == -1) {                
            counter = // Insert code that retrieves the highest value from Google datastore
    }
    counter++;
    return counter;
    }
}

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