[jira] [Created] (CASSANDRA-15442) Read repair implicitly increases read timeout value

["Yifan Cai (Jira)" <ji...@apache.org>]

Yifan Cai created CASSANDRA-15442:
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             Summary: Read repair implicitly increases read timeout value
                 Key: CASSANDRA-15442
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15442
             Project: Cassandra
          Issue Type: Bug
          Components: Legacy/Core
            Reporter: Yifan Cai


When read repair occurs during a read, internally, it starts several _blocking_ operations in sequence. See {{org.apache.cassandra.service.StorageProxy#fetchRows}}. 
 The timeline of the blocking operations
 # Regular read, wait for full data/digest read response to complete. {{reads[*].awaitResponses();}}
 # Read repair read, wait for full data read response to complete. {{reads[*].awaitReadRepair();}}
 # Read repair write, wait for write response to complete. {{concatAndBlockOnRepair(results, repairs);}}

Step 1 and 2 each waits for the duration of read timeout, say 5 s.
 Step 3 waits for the duration of write timeout, say 2 s.
 In the worse case, the actual time taken for a read could accumulate to ~12 s, if each individual step does not exceed the timeout value.
 From the client perspective, it does not expect a request taken way higher than the database configured timeout value. 
 Such scenario is especially bad for the clients that have set up client-side timeout monitoring close to the configured one. The clients think the operations timed out and abort, but they are in fact still running on server.



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