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MongoDB 问题123

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Jun 07, 2016 pm 05:54 PM

mongodbquestion

MongoDB 是非关系型数据库中的一种。出于某些原因，我们用了Mongo。他们说Mongo的最大特点是快。不过这种快是以空间换时间的代价而得来的。这个空间代价包括 1.DB至少占用64M(好像是这个数字，因为我们的DB实际往往只有几M,但却要占用那么多，空间浪费严

MongoDB 是非关系型数据库中的一种。

出于某些原因，我们用了Mongo。他们说Mongo的最大特点是快。

不过这种快是以空间换时间的代价而得来的。

这个空间代价包括

1.DB至少占用64M(好像是这个数字，因为我们的DB实际往往只有几M,但却要占用那么多，空间浪费严重)

2.加载到内存里的数据不会主动释放，虚拟主机，导致服务挂掉了。具体机制不懂，只知道，为了提高速度，香港服务器，Mongo的内存耗费是相当惊人的。

本文主要讲述在实践中碰到的一些Mongo的问题，由于我对Mongo底层的实现机制

不是很了解，有不懂的地方，还希望大牛们能帮解答下。

1.就是DB数量对Mongo的性能及稳定性的影响。

我们是单台数据库服务器，网站空间，实践中，当DB数量过万时，整个Mongo就突然变得极不稳定，随时都会挂掉。

挂掉的直接原因好像是内存不够，由于不是我本人负责的，具体情况我也不知道。

2.Mongo的数据释放

除了DB级别的删除，Mongo会直接释放空间，对于其它像Collection 或 Document层的删除，磁盘空间并没有直接释放。

随着岁月的积累，整个磁盘就会布满碎片。他们使用的一种解决方法是Mongo 自带的repair 命令

3.加载到内存里的数据

首先是索引，然后是命中的数据块，索引的应该是常驻的。命中的数据块是不是一旦进来就不出去了。

为什么会出现前面所说的性能临界点。可不可以手动设置。

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