Cassandra 写入性能与关系数据库
我试图了解 Cassandra 和关系数据库之间的一些性能差异。
据我了解，无论数据量如何，Cassandra 的写入性能都保持不变。通过写入性能，我假设这意味着在关键匹配上添加新行以及替换现有行（就像关系世界中的更新）。这个假设正确吗？
另外，根据我对关系数据库的理解，当表/分区变大时，更新会变慢。这是因为必须执行全表扫描来定位行，或者需要执行索引查找，并且随着表或分区的增长，这两种操作都会花费更长的时间。那么根据表/分区的数据量，更新需要的时间永远更长？
当新数据插入关系数据库时，我知道任何索引都需要有新数据，但没有涉及正确的查找？那么，随着数据量的增加，插入也会变得永远变慢，还是关系数据库保持不变？
感谢您的任何提示
I am trying to grasp some performance differences between Cassandra and relational databases.
From what I have read, Cassandra's write performance remains constant regardless of data volume. By write performance, I am assuming this implies both new rows being added as well as existing rows being replaced on a key match (like an update in the relational world). Is that assumption correct?
Also, from what I understand about relational databases updates get slower when tables/partitions become larger. This is because a full table scan must be performed to locate the row, or an index lookup needs to be performed and both of these things will take longer as the table or partition grows. So updates take perpetually longer based on the data volume of the table/partition?
When new data is inserted to a relational database, I know any indexes need to to have the new data but there is no lookup involved correct? So will inserts also become perpetually slower as data volume increases or stay constant with relational databases?
Thanks for any tips
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如果表有索引，它们会变得更慢。不仅要写入数据，还必须更新索引。插入没有索引且没有约束的表速度快如闪电，因为不需要进行任何检查。记录可以只写在表空间的末尾。
They will become slower if the table has indexes. Not only the data must be written, but the index must be updated too. Inserting in a table that has no indexes and no constraints is lightning fast, because no checks need to be done. The record can just be written at the end of the table space.
在关系数据库方面，我一直在对 RDBMS 进行负载测试，我可以看到随着数据添加到数据库，性能呈指数下降。
我仍在研究 Cassandra 设置，以便能够实现类似的测试。同时，此 Cassandra 演示提供了有关 Cassandra 与 MySQL 的一些信息：
http://www.slideshare.net/Eweaver/cassandra-presentation-at- nosql
On the relational DB side, I've been doing load testing on our RDBMS where I can see that the performance drops exponentially as data is added to the DB.
I'm still working on a Cassandra setup to be able to realize a comparable test. In the meantime, this Cassandra presentation gives some info on Cassandra compared to MySQL:
http://www.slideshare.net/Eweaver/cassandra-presentation-at-nosql