[CASSANDRA-16784] Conditional update on super column table returns too many rows

• Type: Bug
• Status: Open
• Priority: Normal
• Resolution: Unresolved
• Fix Version/s: 3.0.x, 3.11.x
• Component/s: Feature/Lightweight Transactions
• Bug Category: Correctness
• Severity: Normal
• Complexity: Normal
• Discovered By: User Report
• Platform: All
• Assignee: Unassigned
• Reporter: Marten Kenbeek
• Created: 01/Jul/21 15:50
• Updated: 08/Oct/21 12:32

Description

We have a (dense) supercolumn table that we're trying to upgrade from 2.2 to 3.x. On this table we perform conditional updates on one of the values using a CQL query. In 2.2 this works as expected: the query returns either a single-column row with true, or a two-column row with false and the current value.

In 3.x this query is internally rewritten to work on a map, using a Maps.SetterByKey operation. The update itself is applied correctly, but when the condition fails and the update is not applied, the query returns all values in the supercolumn/map instead of just the value of the subcolumn/key from the where clause.

In particular, since it returns just the values, and not the keys/mapping, there's no way to know which of the values is the value of the row we're trying to update.

 

– Super column table (created through Thrift)
 CREATE TABLE store.shopping_items (
 key text,
 column1 text,
 column2 text,
 "" map<text, text>,
 value text,
 PRIMARY KEY (key, column1, column2)
 ) WITH COMPACT STORAGE;
– Create some data
 cqlsh:store> INSERT INTO shopping_items (key, column1, column2, value) VALUES ('item1', 'default', 'id', '1');
 cqlsh:store> INSERT INTO shopping_items (key, column1, column2, value) VALUES ('item1', 'default', 'color', 'blue');
– This query returns multiple rows
 cqlsh:store> UPDATE shopping_items SET value ='2' WHERE key ='item1' AND column1 = 'default' AND column2 = 'id' IF value = null;
[applied] | value
 ----------+-----------
 False | 'blue'
 False | '1'

 

See the attached patch for a test that succeeds on 2.2, but fails with the described behavior on 3.0 and on the latest 3.11.