[jira] [Created] (CASSANDRA-7040) Replace read/write stage with per-disk access coordination

["Benedict (JIRA)" <ji...@apache.org>]

Benedict created CASSANDRA-7040:
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             Summary: Replace read/write stage with per-disk access coordination
                 Key: CASSANDRA-7040
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7040
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Benedict
             Fix For: 3.0


As discussed in CASSANDRA-6995, current coordination of access to disk is suboptimal: instead of ensuring disk accesses alone are coordinated, we instead coordinate at the level of operations that may touch the disks, ensuring only so many are proceeding at once. As such, tuning is difficult, and we incur unnecessary delays for operations that would not touch the disk(s).

Ideally we would instead simply use a shared coordination primitive to gate access to the disk when we perform a rebuffer. This work would dovetail very nicely with any work in CASSANDRA-5863, as we could prevent any blocking or context switching for data that we know to be cached. It also, as far as I can tell, obviates the need for CASSANDRA-5239.



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