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From "Stu Hood (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-2540) Data reads by default
Date Fri, 22 Apr 2011 05:55:06 GMT
Data reads by default

                 Key: CASSANDRA-2540
             Project: Cassandra
          Issue Type: Bug
            Reporter: Stu Hood
             Fix For: 0.8.0

The intention of digest vs data reads is to save bandwidth in the read path at the cost of
latency, but I expect that this has been a premature optimization.

* Data requested by a read will often be within an order of magnitude of the digest size,
and a failed digest means extra roundtrips, more bandwidth
* The [digest reads but not your data read|]
problem means failing QUORUM reads because a single node is unavailable, and would require
eagerly re-requesting at some fraction of your timeout
* Saving bandwidth in cross datacenter usecases comes at huge cost to latency, since both
constraints increase proportionally enough that the tradeoff is not clear

Some options:
# Add an option to use digest reads
# Remove digest reads entirely (and/or punt and make them a runtime optimization based on
data size in the future)

The outcome of data-reads-by-default should be significantly improved latency, with a moderate
increase in bandwidth usage for large reads.

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