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From "Sylvain Lebresne (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1684) Entity groups
Date Thu, 03 Mar 2011 19:28:37 GMT


Sylvain Lebresne commented on CASSANDRA-1684:

bq. Do tokens have to be one-to-one unique with keys, or could you have multiple keys share
the same token? (apparently that's currently possible, although an extreme edge case, with
the RandomPartitioner)

Right now, they do have to be one-to-one. That's the 'raison d'ĂȘtre' of CASSANDRA-1034 (and
I won't hide that my interest for the latter is motivated by this ticket, even though we should
fix it because of RandomPartioner anyway).

As for this ticket, I think using parts of the key for the token is only the first step (but
an important one). The main thing we want here is to apply mutation on an entity group consistently,
that is in one commit log transaction. That in turn is not very complicated in theory, but
will be much more work in practice I believe.

As a side note, I think it would also be nice to find "a trick" to make this work with the
existing partitioners. Otherwise, since we can't change partitioners, this would make this
useful for only new clusters, which would be sad.

> Entity groups
> -------------
>                 Key: CASSANDRA-1684
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sylvain Lebresne
>             Fix For: 0.8
>   Original Estimate: 80h
>  Remaining Estimate: 80h
> Supporting entity groups similar to App Engine's (that is, allow rows to be part of a
parent "entity group," whose key is used for routing instead of the row itself) allows several
>  - batches within an EG can be atomic across multiple rows
>  - order-by-value queries within an EG only have to touch a single replica even with

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