Cassandra ttl 连续 [英] Cassandra ttl on a row

问题描述

我知道 Cassandra 中的列有 TTL.但是也可以在一行上设置 TTL 吗?如以下用例所示，在每列上设置 TTL 并不能解决我的问题:

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:

在某些时候，一个进程想要删除一个带有 TTL 的完整行(假设行A"的 TTL 为 1 周).它可以通过替换具有相同内容但 TTL 为 1 周的所有现有列来实现此目的.

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.

但是 可能有另一个进程在A"行上同时运行，它插入新列或替换没有 TTL 的现有列，因为该进程不知道要删除该行(它同时运行！).因此，1 周后，除了这些新插入的列之外，A"行的所有列都将因 TTL 被删除.我也希望它们被删除.

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.

那么这个用例是否有或将有 Cassandra 支持，还是我必须自己实现一些东西?

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

亲切的问候
斯蒂芬

Kind Regards
Stefan

推荐答案

目前在 Cassandra 中没有办法在一行上设置 TTL.TTL 设计用于在写入时已知其生命周期时删除单个列.

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.

您可以通过延迟过程来实现您想要的 - 而不是想要插入 1 周的 TTL，而是在一周后运行它并删除该行.行删除具有以下语义:之前插入的任何列都会被删除，但之后插入的列不会被删除.

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删除，您可以在将来插入带有时间戳的行删除以确保这一点，但要非常小心:如果您以后想插入该行，则不能，写入该行时，列就会消失(直到墓碑被垃圾收集).

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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