[CASSANDRA-5945] CAS transactions permitting multiple updates

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Component/s: Feature/Lightweight Transactions
• Labels: LWT

Environment

3 node Cassandra 2.0.0-rc2 cluster
Java driver 1.0.2
Replication factor 3
Quorum consistency

• Severity: Normal
• Assignee: Unassigned
• Reporter: Phil Persad
• Created: 27/Aug/13 21:26
• Updated: 25/Oct/19 13:10
• Resolved: 20/Nov/13 00:58

Description

This bug is spawned off CASSANDRA-5925 to track an underlying issue not related to TTLs. To reproduce:

Step 1:

CREATE TABLE IF NOT EXISTS tkns (tkn blob, consumed boolean, PRIMARY KEY (tkn));

Step 2:

INSERT INTO tkns (tkn, consumed) VALUES (?,FALSE);

Step 3:

UPDATE tkns SET consumed = TRUE WHERE tkn = ? IF consumed = FALSE;

Step 4:

UPDATE tkns SET consumed = TRUE WHERE tkn = ? IF consumed = FALSE;

Repeat steps 2-4 about 100,000 times.

Expectation:

For the '[applied]' column in the result sets for steps 3 and 4, exactly one should be true and one should be false.

Bug:

In a small number of cases (varying from 0.002% to 1%) both updates will report success. See attached unit test.

Issue Links

• relates to: CASSANDRA-5925 Race condition in update lightweight transaction