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Jeff Jirsa commented on CASSANDRA-11637:
----------------------------------------
Riak's docs for {{notfound_ok}} :
{quote}
This parameter determines how Riak responds if a read fails on a node. Setting
to true (the default) is the equivalent to setting R to 1: if the first node to
respond doesn’t have a copy of the object, Riak will immediately return a not
found error. If set to false, Riak will continue to look for the object on the
number of nodes specified by N (aka n_val).
{quote}
While you could handle this at the driver level by increasing consistency on a
null result, it seems that if client could explicitly instruct/allow the
coordinator to return as soon as any replica had a non-empty result, it may
make reads safely faster for some data models and save the extra query.
> Immutable-friendly read consistency level
> ------------------------------------------
>
> Key: CASSANDRA-11637
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11637
> 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. {{QUORUM}}).
> 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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