Richard Low created CASSANDRA-7592:
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Summary: Ownership changes can violate consistency
Key: CASSANDRA-7592
URL: https://issues.apache.org/jira/browse/CASSANDRA-7592
Project: Cassandra
Issue Type: Improvement
Reporter: Richard Low
CASSANDRA-2434 goes a long way to avoiding consistency violations when growing
a cluster. However, there is still a window when consistency can be violated
when switching ownership of a range.
Suppose you have replication factor 3 and all reads and writes at quorum. The
first part of the ring looks like this:
Z: 0
A: 100
B: 200
C: 300
Choose two random coordinators, C1 and C2. Then you bootstrap node X at token
50.
Consider the token range 0-50. Before bootstrap, this is stored on A, B, C.
During bootstrap, writes go to X, A, B, C (and must succeed on 3) and reads
choose two from A, B, C. After bootstrap, the range is on X, A, B.
When the bootstrap completes, suppose C1 processes the ownership change at t1
and C2 at t4. Then the following can give an inconsistency:
t1: C1 switches ownership.
t2: C1 performs write, so sends write to X, A, B. A is busy and drops the
write, but it succeeds because X and B return.
t3: C2 performs a read. It hasn’t done the switch and chooses A and C. Neither
got the write at t2 so null is returned.
t4: C2 switches ownership.
This could be solved by continuing writes to the old replica for some time
(maybe ring delay) after the ownership changes.
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