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From "Robert Stupp (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-11637) Immutable-friendly read consistency level
Date Mon, 25 Apr 2016 13:19:12 GMT


Robert Stupp commented on CASSANDRA-11637:

Hmm - what could C* do _better_ compared to the application increasing the CL from ONE to
QUORUM? I mean, the probability that you hit that situation (let's call it the "eventual-consistency
time window") is fairly low. In fact, this would have to be done on the coordinator level
- so you'd just save the roundtrip from the application to the coordinator.

> Immutable-friendly read consistency level 
> ------------------------------------------
>                 Key: CASSANDRA-11637
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: lvh
>            Priority: Minor
> Many Cassandra applications use immutable, append-only models. For those models, you
can accept read consistency {{ONE}}, since the data either exists (and then it's the data
you want) or it doesn't. However, it's possible that the data hasn't made it to that node
yet, so "missing" data might mean "actually missing" or "not here".
> Riak has a convenient read consistency option for this, called notfound_ok (default true).
When false, the first succeeding read will succeed the operation (a la consistency level {{ONE}}),
but a missing read from any node will keep trying up to the normal consistency level (e.g.
> The workaround for this is for applications to implement an "UpgradingConsistencyPolicy"
(dual to DowngradingConsistencyPolicy) that tries e.g. {{QUORUM}} after {{ONE}} fails, and
then writes with e.g. {{QUORUM}}.
> This is related to CASSANDRA-9779; but it seems that ticket only explores the compaction/collation/materialized
view angle, not the fast & safe read consistency angle.
> Thanks to [~jjirsa]] for helping me dig through this, find the related ticket, and confirm
Cassandra currently does not support this.

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