[CASSANDRA-9086] CAS precondition mismatch - row is still inserted

• Type: Bug
• Status: Resolved
• Priority: Urgent
• Resolution: Not A Problem
• Fix Version/s: 2.0.15
• Component/s: Feature/Lightweight Transactions
• Labels: LWT

Environment

Cassandra version 2.0.11
24 nodes in 4 datacenters (6 nodes per dc)

• Severity: Critical
• Assignee: Carl Yeksigian
• Reporter: Roger Schildmeijer

Authors

Carl Yeksigian

• Created: 01/Apr/15 14:24
• Updated: 25/Oct/19 13:11
• Resolved: 14/Apr/15 16:13

Description

Cassandra claims CAS precondition didn't match current values[1], but the row is still inserted.

We are having a quite simple cf schema:

create table index (
  u text PRIMARY KEY,
  abc set<uuid>,
) WITH
  compaction={'class': 'LeveledCompactionStrategy'};

CQL statement:

INSERT INTO index(u, abc) VALUES(?, ?) IF NOT EXISTS

Sometimes, especially during some write load, Cassandra claims the conditional insert wasn't satisfied ([applied] false), but the row is still inserted.

The response from the conditional insert contains [applied]=false + the data we tried to insert.

A full CQL trace is attached.

[1] CAS precondition CAS precondition org.apache.cassandra.cql3.statements.CQL3CasConditions@1b2576ce does not match current values ColumnFamily(username_index -

{deletedAt=-9223372036854775808, localDeletion=2147483647, ranges=[abc-abc:!, deletedAt=1427889576525999, localDeletion=1427889564]}

- [:false:0@1427889576526000,abc:39f1a470ee694761a8197c0d0ada8e8f:false:0@1427889576526000,]) | 11:59:37.060 | /10.0.0.1 | 533702