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Date: Wed, 25 Jun 2014 17:16:27 +0000 (UTC)
From: "Peter Bailis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Message-ID: <JIRA.12709314.1397844880632.47542.1403716587328@arcas>
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Subject: [jira] [Comment Edited] (CASSANDRA-7056) Add RAMP transactions
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    [ 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:
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> 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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