cassandra大量写入性能问题
我的服务器配备 4 GB RAM 和 2x 4 核 CPU。当我开始在 Cassandra 中执行大量写入时，最初一切正常，但几个小时后，每秒 10K 插入，数据库增长到 25+ GB，性能下降到每秒 500 次插入！
我发现这是因为压缩操作非常慢，但我不明白为什么？我设置了 8 个并发压缩线程，但 Cassandra 不使用 8 个线程；仅加载 2 个核心。
感谢任何帮助。
I have server with 4 GB RAM and 2x 4 cores CPU. When I start perform massive writes in Cassandra all works fine initially, but after a couple hours with 10K inserts per second database grows up to 25+ GB, and performance go down to 500 insert per seconds!
I find out this because compacting operations is very slow but I don't understand why? I set 8 concurrent compacting threads but Cassandra don't use 8 threads; only 2 cores are loaded.
Appreciate any help.
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我们已经在 Cassandra 开箱即用中看到了类似的问题，请参阅：
http://www.acunu.com/blogs/richard-low/cassandra-under-heavy-write-load-part-ii/
解决此类性能下降的一种解决方案问题（但是绝不是唯一的）是考虑使用不同的存储引擎，例如上面博客文章中使用的 Castle - 它的开源（GPL v2），具有更好的性能并且更优雅地降级。代码在这里（我刚刚推出了 Cassandra 0.8 支持的分支）：
https://bitbucket。 org/acunu/fs.hg
有关如何开始的说明如下：
http://support.acunu.com/entries/20216797-castle-build-instructions
（全面披露：我为 Acunu 工作，所以可能有点偏见；-）
We've seen similar problems with Cassandra out-the-box, see:
http://www.acunu.com/blogs/richard-low/cassandra-under-heavy-write-load-part-ii/
One solution to these sort of performance degradation issues (but by no means the only) is to consider a different storage engine, like Castle, used in the above blog post - its opensource (GPL v2), has much better performance and degrades much more gracefully. The code is here (I've just pushed up a branch for Cassandra 0.8 support):
https://bitbucket.org/acunu/fs.hg
And instructions on how to get started are here:
http://support.acunu.com/entries/20216797-castle-build-instructions
(Full disclosure: I work for Acunu, so may be a little biased ;-)