Cassandra ttl在行 [英] Cassandra ttl on a row

问题描述

我知道Cassandra的列上有TTL。但是是否也可以在行上设置TTL？在每个列上设置TTL不能解决我的问题，如下面的用例所示：

I know that there are TTLs on columns in Cassandra. But is it also possible to set a TTL on a row? Setting a TTL on each column doesn't solve my problem as can be seen in the following usecase:

在某一时刻，进程要删除一个具有TTL的完整行（假设行A，TTL为1周）。

At some point a process wants to delete a complete row with a TTL (let's say row "A" with TTL 1 week). It could do this by replacing all existing columns with the same content but with a TTL of 1 week.

但可能会有另一个进程正在运行同时在插入新列或替换没有TTL的现有行的行A，因为该进程不知道该行将被删除（它并行运行）。因此，在1周后，除了这些新插入的行之外，由于TTL的行A的所有列将被删除。

But there may be another process running concurrently on that row "A" which inserts new columns or replaces existing ones without a TTL because that process can't know that the row is to be deleted (it runs concurrently!). So after 1 week all columns of row "A" will be deleted because of the TTL except for these newly inserted ones. And I also want them to be deleted.

那么，还是会有Cassandra支持这个用例，还是我自己实现呢？

So is there or will there be Cassandra support for this use case or do I have to implement something on my own?

种类问题
Stefan

Kind Regards
Stefan

推荐答案

没有办法在Cassandra中的一行上设置TTL。 TTL的设计用于删除单独的列，当他们的生命周期知道他们写的时候。

There is no way of setting a TTL on a row in Cassandra currently. TTLs are designed for deleting individual columns when their lifetime is known when they are written.

您可以通过延迟您的过程实现您想要的，而不是想插入一个TTL的1周，运行一个星期后，删除该行。行删除具有以下语义：任何刚刚插入的列都将被删除，但刚刚插入的列将不会被删除。

You could achieve what you want by delaying your process - instead of wanting to insert a TTL of 1 week, run it a week later and delete the row. Row deletes have the following semantics: any column inserted just before will get deleted but columns inserted just after won't be.

如果将来插入的列仍然需要要删除，你可以在将来插入一个时间戳记删除，以确保这一点，但要非常小心：如果你后来想插入到那行，你不能，列只会消失，当写到那一行（直到墓碑是垃圾收集）。

If columns that are inserted in the future still need to be deleted you could insert a row delete with a timestamp in the future to ensure this but be very careful: if you later wanted to insert into that row you couldn't, columns would just disappear when written to that row (until the tombstone is garbage collected).

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