Theo Hultberg created CASSANDRA-6601:
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Summary: WRITETIME of a null value does not return a time
Key: CASSANDRA-6601
URL: https://issues.apache.org/jira/browse/CASSANDRA-6601
Project: Cassandra
Issue Type: Bug
Environment: Cassandra 2.0.2
Reporter: Theo Hultberg
When a cell's value is {{null}} the CQL {{WRITETIME}} function returns null. I
was expecting it to return a timestamp. Looking at the data in
{{cassandra-cli}} I can see that the cell has a timestamp.
Here's a session showing the issue:
{code}
cqlsh> CREATE KEYSPACE writetime_test WITH replication = {'class':
'SimpleStrategy','replication_factor': '1'};
cqlsh> USE writetime_test;
cqlsh:writetime_test> CREATE TABLE writetime_test_table (pk INT, ck INT, value
INT, PRIMARY KEY (pk, ck));
cqlsh:writetime_test> INSERT INTO writetime_test_table (pk, ck, value) VALUES
(1, 2, null);
cqlsh:writetime_test> SELECT WRITETIME(value) FROM writetime_test_table WHERE
pk = 1 AND ck = 2;
writetime(value)
------------------
null
(1 rows)
cqlsh:writetime_test> INSERT INTO writetime_test_table (pk, ck, value) VALUES
(2, 3, 4);
cqlsh:writetime_test> SELECT WRITETIME(value) FROM writetime_test_table WHERE
pk = 2 AND ck = 3;
writetime(value)
------------------
1389967663822000
(1 rows)
cqlsh:writetime_test> SELECT WRITETIME(value) FROM writetime_test_table WHERE
pk = 3 AND ck = 4;
(0 rows)
{code}
I first insert data where the cell value is {{null}}. When I query its
writetime I get a row back, but the timestamp is {{null}}.
I then insert a row with a value, and get a timestamp in the query results, as
expected.
Finally I query for the writetime of a cell that does not exist, and get no
rows back, just to show that there's a difference between calling {{WRITETIME}}
on {{null}} and on something that doesn't exist.
Even though the value is {{null}} the cell exists and it has a timestamp. I can
clearly see the timestamp using {{cassandra-cli}}:
{code}
[default@unknown] use writetime_test;
Authenticated to keyspace: writetime_test
[default@writetime_test] list writetime_test_table;
Using default limit of 100
Using default cell limit of 100
-------------------
RowKey: 1
=> (name=2:, value=, timestamp=1389967959822000)
-------------------
RowKey: 2
=> (name=3:, value=, timestamp=1389967964749000)
=> (name=3:value, value=00000004, timestamp=1389967964749000)
{code}
The reason I want to get the {{WRITETIME}} of a {{null}} value is that I have a
table where I don't care about the value, I use the column keys as sorted set.
I still want to know when some of them were written though, but I can't ask for
the {{WRITETIME}} of something that is part of the primary key, so I must use
the (otherwise unused) value.
A workaround is to write some dummy value in the cell, and that's probably what
I need to do, but this felt like it was a bug, it was at least not what I
expected.
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