Tyler Hobbs created CASSANDRA-10414:
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Summary: Add Internal Support for Reading Multiple Token Ranges
with Single Command
Key: CASSANDRA-10414
URL: https://issues.apache.org/jira/browse/CASSANDRA-10414
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Tyler Hobbs
Fix For: 3.x
Since CASSANDRA-1337, we've parallelized fetches of multiple token ranges when
handling range slices or secondary index queries. However, a separate command
still needs to be created, issued, and handled for (almost) every token range.
With vnodes enabled, the number of commands to handle becomes quite large,
introducing a lot of extra overhead. If we allow ReadCommands to contain
multiple token ranges instead of a single range, we could significantly improve
this.
A secondary bonus of doing this is that we will reduce over-fetching of rows.
Right now, each command uses the same total limit. If some of the token ranges
have more rows than we expect (based on the average partition size and key
estimates), the replicas will over-fetch rows, only for them to be discarded by
the coordinator. In the worst case scenario, each token range could contain
LIMIT rows. With a multi-range command we could still have overfetching, but
it would be more tightly bounded: each node could return at most LIMIT rows
(across all token ranges combined).
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