blocks|key|3749381|text|我们在一个大型客户端/服务器项目中运行DB40+.NET版本。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3749382|我们的经验是，与典型的关系数据库相比，您可以获得更好的性能。|3749383|然而，你真的需要调整你的对象来获得这种性能。例如，如果您有一个包含大量对象的列表，则这些列表的DB4O激活速度会很慢。有许多方法可以绕过这个问题，例如，通过颠倒关系。|3749384|另一个痛苦是激活。从DB4O检索或删除对象时，默认情况下将激活整个对象树。例如，加载Foo将加载Foo.Bar.Baz.Bat，等等，直到没有剩余可加载的内容。虽然从编程的角度来看这很好，但在对象中嵌套越多，性能就会越慢。要提高性能，您可以告诉DB4O要激活多少层。如果你有很多对象，这是很耗时的。|3749385|另一个痛苦的领域是文本搜索。DB4O的文本搜索比SQL全文索引慢得多。(他们会在他们的网站上直接告诉你。)好消息是，在DB4O上设置文本搜索引擎很容易。在我们的项目中，我们连接了Lucene.NET来索引我们想要的文本字段。|3749386|有些API似乎不起作用，例如在应用数据库升级时有用的GetField+API。(例如，您已经重命名了一个属性，并且想要升级数据库中的现有对象，则需要使用这些“反射”API来查找数据库中的对象。其他.Index，比如Index属性，在稳定的6.4版本中不起作用，您必须使用Configure()API(“someField”)来指定索引，该API不是强类型的。|3749387|我们已经看到，数据库越大，性能就越差。我们现在有一个1+1GB的数据库，速度仍然很快，但没有我们刚开始使用一个小数据库时那么快。|3749388|我们发现了另一个问题，如果该ID在数据库中不再存在，Db4O.GetByID将关闭数据库。|3749389|我们发现原生查询语法(最自然的、语言集成的查询语法)比不太友好的SODA查询慢得多。因此，与其键入：|3749390|//+C#+syntax+for+"Find+all+MyFoos+with+Bar+==+23".
//+(Note+the+Java+syntax+is+more+verbose+using+the+Predicate+class.)
IList<MyFoo>+results+=+db4o.Query<MyFoo>(input+=>+input.Bar+==+23);|code-block|syntax|javascript|3749391|您必须使用基于字符串且不是强类型丑陋的SODA查询，而不是很好的查询代码。|3749392|对于.NET人员来说，他们最近引入了一个LINQtoDB4O提供程序，它提供了迄今为止最好的语法。然而，性能是否会达到丑陋的SODA查询还有待观察。|3749393|DB4O的支持一直很好:我们已经和他们通了几次电话，并收到了有用的信息。他们的用户论坛几乎一文不值，然而，几乎所有的问题都没有答案。他们的JIRA+bug追踪器受到了很多关注，所以如果你有一个纠缠不休的bug，把它归档到JIRA上就会得到修复。(我们已经修复了两个bug，另一个已经以半成功的方式完成了修补。)|3749394|如果所有这些都没有吓跑你，让我说我们对DB4O非常满意，尽管我们遇到了很多问题。我们所获得的性能让我们尝试过的一些O/RM框架大吃一惊。我推荐它。|3749395|更新2015年7月请记住，这个答案是在2008年写的。虽然我很感谢大家的好评，但从那时起，世界已经发生了变化，这些信息可能不像写它时那么可靠了。|offset|length|style|BOLD|3749396|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|9|0^^$0|@$1|2|3|4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1D|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1E|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1F|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|1G|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1H|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|1I|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|1J|8|@]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1K|8|@]|9|@]|A|$]]|$1|R|3|S|5|T|7|1L|8|@]|9|@]|A|$U|V]]|$1|W|3|X|5|6|7|1M|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1N|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1O|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1P|8|@]|9|@]|A|$]]|$1|14|3|15|5|6|7|1Q|8|@$16|1R|17|1S|18|19]]|9|@]|A|$]]|$1|1A|3|-4|5|6|7|1T|8|@]|9|@]|A|$]]]|1B|$]]

We run DB40 .NET version in a large client/server project.

Our experiences is that you can potentially get much better performance than typical relational databases.

However, you really have to tweak your objects to get this kind of performance. For example, if you've got a list containing a lot of objects, DB4O activation of these lists is slow. There are a number of ways to get around this problem, for example, by inverting the relationship.

Another pain is activation. When you retrieve or delete an object from DB4O, by default it will activate the whole object tree. For example, loading a Foo will load Foo.Bar.Baz.Bat, etc until there's nothing left to load. While this is nice from a programming standpoint, performance will slow down the more nesting in your objects. To improve performance, you can tell DB4O how many levels deep to activate. This is time-consuming to do if you've got a lot of objects.

Another area of pain was text searching. DB4O's text searching is far, far slower than SQL full text indexing. (They'll tell you this outright on their site.) The good news is, it's easy to setup a text searching engine on top of DB4O. On our project, we've hooked up Lucene.NET to index the text fields we want.

Some APIs don't seem to work, such as the GetField APIs useful in applying database upgrades. (For example, you've renamed a property and you want to upgrade your existing objects in the database, you need to use these "reflection" APIs to find objects in the database. Other APIs, such as the [Index] attribute don't work in the stable 6.4 version, and you must instead specify indexes using the Configure().Index("someField"), which is not strongly typed.

We've witnessed performance degrade the larger your database. We have a 1GB database right now and things are still fast, but not nearly as fast as when we started with a tiny database.

We've found another issue where Db4O.GetByID will close the database if the ID doesn't exist anymore in the database.

We've found the Native Query syntax (the most natural, language-integrated syntax for queries) is far, far slower than the less-friendly SODA queries. So instead of typing:

<pre><code>// C# syntax for "Find all MyFoos with Bar == 23".
// (Note the Java syntax is more verbose using the Predicate class.)
IList&lt;MyFoo&gt; results = db4o.Query&lt;MyFoo&gt;(input =&gt; input.Bar == 23);
</code></pre>

Instead of that nice query code, you have to an ugly SODA query which is string-based and not strongly-typed.

For .NET folks, they've recently introduced a LINQ-to-DB4O provider, which provides for the best syntax yet. However, it's yet to be seen whether performance will be up-to-par with the ugly SODA queries.

DB4O support has been decent: we've talked to them on the phone a number of times and have received helpful info. Their user forums are next to worthless, however, almost all questions go unanswered. Their JIRA bug tracker receives a lot of attention, so if you've got a nagging bug, file it on JIRA on it often will get fixed. (We've had 2 bugs that have been fixed, and another one that got patched in a half-assed way.)

If all this hasn't scared you off, let me say that we're very happy with DB4O, despite the problems we've encountered. The performance we've got has blown away some O/RM frameworks we tried. I recommend it.

update July 2015 Keep in mind, this answer was written back in 2008. While I appreciate the upvotes, the world has changed since then, and this information may not be as reliable as it was when it was written.

blocks|key|705177|text|我遇到的主要问题是报告。似乎没有任何方法可以针对db4o数据源运行有效的报告。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|705178|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Main problem I've encountered with it is reporting. There just doesn't seem to be any way to run efficient reports against a db4o data source.

blocks|key|5160382|text|大多数原生查询可以在幕后有效地转换为SODA查询，因此这不会有什么不同。使用NQ当然是首选，因为您仍然停留在强类型语言的领域中。如果您在让NQ使用索引时遇到问题，请随时将您的问题发布到db4o+forums，我们将尽力帮助您解决问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5160383|Goran|5160384|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.db4o.com/forums/^0|2K|B|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Most native queries can and are efficiently converted into SODA queries behind the scenes so that should not make a difference. Using NQ is of course preferred as you remain in the realms of strong typed language. If you have problems getting NQ to use indexes please feel free to post your problem to the <a href="http://developer.db4o.com/forums/" rel="nofollow noreferrer">db4o forums</a> and we'll try to help you out.

Goran

blocks|key|3749578|text|犹大，听起来你没有使用透明激活，这是最新的生产版本(7.4)的一个特性？也许，如果您指定了您正在使用的版本，因为可能存在其他问题，这些问题现在已在最新版本中得到解决。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3749579|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Judah, it sounds like you are not using transparent activation, which is a feature of the latest production version (7.4)? Perhaps if you specified the version you are using as there may be other issues which are now resolved in the latest version?

I'm currently trying out db4o (the java version) and I pretty much like what I see. But I cannot help wondering how it does perform in a real live (web-)environment. Does anyone have any experiences (good or bad) to share about running db4o?

db4o experiences?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我目前正在试用db4o ( java版)，我非常喜欢我所看到的。但我不禁想知道它在真实的(网络)环境中的表现如何。有没有人有什么运行db4o的经验(好的或者不好的)来分享？

问db4o体验？
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