DELETE存储在特定节点上的行 [英] DELETE rows stored on a particular node

问题描述

我如何写一个CQL 3 DELETE 行规范（ WHERE 它将只选择存储在给定节点上的行？如果不可能，是否有 SELECT 关系（ WHERE 指示哪些行存储在特定节点上？

我想这样做，因此我可以在每个数据存储节点上运行一个管理守护进程（在Java中）从该节点删除旧记录，因此可以确保其节点不会耗尽磁盘空间。因为我在写一个守护进程，而不是执行一次性清理，不适合使用 nodetool 程序查询存储在节点上的令牌范围。 / p>

解决方案

这里有一种方法可行（但是下面有更好的想法）。如果您没有启用vnode，您可以标识令牌范围（从 nodetool ring 命令），然后将其用作delete命令的一部分。例如：

 从MyTable中删除其中
令牌（MyPK）> = Token1和
令牌MyPK） Token2和
（这里你的删除逻辑）
;但是，一个更简单和更安全的方法是让Cassandra知道数据在哪里，然后，只需从任何节点执行此操作：
 从MyTable中删除其中
 ; 
  
 
How can I write a CQL 3 DELETE row specification (WHERE clause) that will select only rows that are stored on a given node? If that is not possible, is there a SELECT relation (WHERE clause) that will indicate which rows are stored on a particular node?

I want to do this so I can have a housekeeping daemon (in Java) running on each data-store node, which deletes old records from that node, so it can ensure that its node does not run out of disk space. As I am writing a daemon, rather than performing a one-off cleanup, it is not appropriate to use the nodetool program to query for the token ranges stored on a node.
解决方案
Here's one way that might work (but see below for a better idea). If you don't have vnodes enabled, you could identify the token ranges (from then nodetool ring command), then use them as part of your delete command. For example:
delete from MyTable where 
    token(MyPK) >= Token1 and 
    token(MyPK) < Token2 and
    (your delete logic here)
;
However, a much simpler and safer method would be to just let Cassandra figure out where the data is, and just do this from any node:
delete from MyTable where 
    (your delete logic here)
;


                        
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