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From "Theo Hultberg (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-6601) WRITETIME of a null value does not return a time
Date Mon, 20 Jan 2014 10:38:19 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-6601?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13876324#comment-13876324
] 

Theo Hultberg commented on CASSANDRA-6601:
------------------------------------------

Thank you for trying to help me understand, and thanks for the optimized version of my workaround.
Using compact storage sounds like a good idea. I use an int column and a zero, and I guess
those would be the same size (an empty blob is just the size prefix of four bytes, and an
int is just the four bytes, IIRC).

I'll stop beating this dead horse now. I might have understood what's going on.

> 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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