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From "Peter Bailis (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-7056) Add RAMP transactions
Date Wed, 25 Jun 2014 17:16:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14043771#comment-14043771
] 

Peter Bailis edited comment on CASSANDRA-7056 at 6/25/14 5:16 PM:
------------------------------------------------------------------

> RAMP has a requirement that anything being read/written that way is always written in
the same groupings. If you update B,C and then update A,B. You can't read B,C anymore successfully,
as the times on B and C will never match.

This isn't entirely correct. Let's say I do an atomic batch B1 that writes B = 1 and C = 1
with timestamp 1, then you do an atomic batch B2 that writes A = 2 and B = 2 at timestamp
2. Under RAMP, subsequent batch reads from B and C will return B = 2, C = 1. The timestamps
on B and C will indeed--as you point out--never match, but simply returning matching timestamps
is *not* not the goal: the goal is that if you read any write in a given batch, you will read
the rest of the writes in the batch (to the items you requested in the batch read)



was (Author: pbailis):
> RAMP has a requirement that anything being read/written that way is always written in
the same groupings. If you update B,C and then update A,B. You can't read B,C anymore successfully,
as the times on B and C will never match.

This isn't entirely correct. Let's say I do an atomic batch B1 that writes B = 1 and C = 1
with timestamp 1, then you do an atomic batch B2 that writes A = 2 and B = 2 at timestamp
2. Under RAMP, subsequent batch reads from B and C will return B = 2, C = 1. The timestamps
on B and C will indeed---as you point out---never match, but simply returning matching timestamps
is *not* not the goal: the goal is that if you read any write in a given batch, you will read
the rest of the writes in the batch (to the items you requested in the batch read)


> Add RAMP transactions
> ---------------------
>
>                 Key: CASSANDRA-7056
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7056
>             Project: Cassandra
>          Issue Type: Wish
>          Components: Core
>            Reporter: Tupshin Harper
>            Priority: Minor
>
> We should take a look at [RAMP|http://www.bailis.org/blog/scalable-atomic-visibility-with-ramp-transactions/]
transactions, and figure out if they can be used to provide more efficient LWT (or LWT-like)
operations.



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