lvh created CASSANDRA-11637:
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Summary: 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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