[CASSANDRA-4579] CQL queries using LIMIT sometimes missing results

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 1.2.0 beta 1
• Labels: cql cql3
• Severity: Normal
• Assignee: Sylvain Lebresne
• Reporter: paul cannon

Authors

Sylvain Lebresne

Reviewers

Pavel Yaskevich

• Created: 27/Aug/12 20:51
• Updated: 16/Apr/19 09:32
• Resolved: 18/Sep/12 06:35

Description

In certain conditions, CQL queries using LIMIT clauses are not being given all of the expected results (whether unset column values or missing rows).

Here are the condition sets I've been able to identify:

First mode: all rows are returned, but in the last row of results, all columns which are not part of the primary key receive no values, except for the first non-primary-key column. Conditions:

• Table has a multi-component primary key
• Table has more than one column which is not a component of the primary key
• The number of results which would be returned by a query is equal to or more than the specified LIMIT

Second mode: result has fewer rows than it should, lower than both the LIMIT and the actual number of matching rows. Conditions:

• Table has a single-column primary key
• Table has more than one column which is not a component of the primary key
• The number of results which would be returned by a query is equal to or more than the specified LIMIT

It would make sense to me that this would have started with CASSANDRA-4329, but bisecting indicates that this behavior started with commit 91bdf7fb4220b27e9566c6673bf5dbd14153017c, implementing CASSANDRA-3647.

Test case for the first failure mode:

DROP KEYSPACE test;

CREATE KEYSPACE test
    WITH strategy_class = 'SimpleStrategy'
    AND strategy_options:replication_factor = 1;

USE test;

CREATE TABLE testcf (
    a int,
    b int,
    c int,
    d int,
    e int,
    PRIMARY KEY (a, b)
);

INSERT INTO testcf (a, b, c, d, e) VALUES (1, 11, 111, 1111, 11111);
INSERT INTO testcf (a, b, c, d, e) VALUES (2, 22, 222, 2222, 22222);
INSERT INTO testcf (a, b, c, d, e) VALUES (3, 33, 333, 3333, 33333);
INSERT INTO testcf (a, b, c, d, e) VALUES (4, 44, 444, 4444, 44444);

SELECT * FROM testcf;

SELECT * FROM testcf LIMIT 1; -- columns d and e in result row are null
SELECT * FROM testcf LIMIT 2; -- columns d and e in last result row are null
SELECT * FROM testcf LIMIT 3; -- columns d and e in last result row are null
SELECT * FROM testcf LIMIT 4; -- columns d and e in last result row are null
SELECT * FROM testcf LIMIT 5; -- results are correct (4 rows returned)

Test case for the second failure mode:

CREATE KEYSPACE test
    WITH strategy_class = 'SimpleStrategy'
    AND strategy_options:replication_factor = 1;

USE test;

CREATE TABLE testcf (
    a int primary key,
    b int,
    c int,
);

INSERT INTO testcf (a, b, c) VALUES (1, 11, 111);
INSERT INTO testcf (a, b, c) VALUES (2, 22, 222);
INSERT INTO testcf (a, b, c) VALUES (3, 33, 333);
INSERT INTO testcf (a, b, c) VALUES (4, 44, 444);

SELECT * FROM testcf;

SELECT * FROM testcf LIMIT 1; -- gives 1 row
SELECT * FROM testcf LIMIT 2; -- gives 1 row
SELECT * FROM testcf LIMIT 3; -- gives 2 rows
SELECT * FROM testcf LIMIT 4; -- gives 2 rows
SELECT * FROM testcf LIMIT 5; -- gives 3 rows