[CASSANDRA-11068] Entire row is compacted away if remaining cells are tombstones expiring after gc_grace_seconds

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Duplicate
• Severity: Normal
• Assignee: Sylvain Lebresne Assign to me
• Reporter: Andy Tolbert

Authors

Sylvain Lebresne

• Created: 25/Jan/16 19:09
• Updated: 16/Apr/19 09:30
• Resolved: 08/Feb/16 11:37

Description

Assuming the following schema:

CREATE TABLE simple.data (
    k text PRIMARY KEY,
    v int
) WITH gc_grace_seconds = 300;

And the following queries:

insert into simple.data (k, v) values ('blah', 1);
delete v from simple.data where k='blah';

Performing a select * from this table will return 1 row with a null value:

cqlsh> select * from simple.data;

         k | v
-----------+---------
      blah |    null

Prior the 3.0, if I were to do a flush, the sstable representation of this table would include an empty cell and a tombstone:

[
{"key": "blah",
 "cells": [["","",1453747038457027],
           ["v",1453747112,1453747112383096,"d"]]}
]

As my gc_grace_seconds value is 300, if I wait 5 minutes and perform a compaction, the new sstable would omit the tombstone, but the empty cell would still be present:

[
{"key": "blah",
 "cells": [["","",1453747038457027]]}
]

Performing the select * query would still yield the same result because of this.

However, in 3.2.1 this does not seem to be the behavior, after deleting the 'v' cell, performing a flush and then waiting 5 minutes and doing a compact, what ends up happening is that the sstable completely disappears (presumably because there is no remaining data) and the select query emits 0 rows:

cqlsh> select * from simple.data;

         k | v
-----------+---------

(0 rows)

I'm unsure if this is by design or a bug, but it does represent a change between C* versions.

I have not tried this for a table with clustering columns yet, but I assume that the behavior will be the same. (The problem only manifests for tables with no clustering columns).

Issue Links

• duplicates: CASSANDRA-11102 Data lost during compaction