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Posted to commits@cassandra.apache.org by "Andreas Andersen (JIRA)" <ji...@apache.org> on 2019/04/01 10:09:03 UTC
[jira] [Commented] (CASSANDRA-15064) Wrong ordering for timeuuid
fields
[ https://issues.apache.org/jira/browse/CASSANDRA-15064?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16806602#comment-16806602 ]
Andreas Andersen commented on CASSANDRA-15064:
----------------------------------------------
As for our use case we can simply use the gocql.TimeUUIDWith function ([https://github.com/gocql/gocql/blob/master/uuid.go#L132]) and supply our own clock sequence. We will never have more than 2^14 images created on a single second.
When it comes to the cassandra part, simply changing the underlying field from a timeuuid to a uuid will solve all of our problems. It sorts in the way we expect it to.
Having the behavior for timeuuid fields mentioned in the cassandra documentation would have been sufficient for solving our problems - we would simply have gone with the uuid datatype from the start. So simply adding more information to the docs seems like a good solution to this issue :)
> Wrong ordering for timeuuid fields
> ----------------------------------
>
> Key: CASSANDRA-15064
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15064
> Project: Cassandra
> Issue Type: Bug
> Components: Cluster/Schema
> Reporter: Andreas Andersen
> Assignee: Jon Meredith
> Priority: Normal
> Attachments: example.cql
>
>
> Hi!
> We're seeing some strange behavior for the ordering of timeuuid fields. They seem to be sorted in the wrong order when the clock_seq_low field in a timeuuid goes from 7f to 80. Consider the following example:
> {noformat}
> cqlsh:test> show version;
> [cqlsh 5.0.1 | Cassandra 3.11.4 | CQL spec 3.4.4 | Native protocol v4]
> cqlsh:test> CREATE TABLE t (
> ... partition int,
> ... t timeuuid,
> ... i int,
> ...
> ... PRIMARY KEY(partition, t)
> ... )
> ... WITH CLUSTERING ORDER BY(t ASC);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b57e-f0def1d0755e, 1);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b57f-f0def1d0755e, 2);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b580-f0def1d0755e, 3);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b581-f0def1d0755e, 4);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b582-f0def1d0755e, 5);
> cqlsh:test> SELECT * FROM t WHERE partition = 1 ORDER BY t ASC;
>
> partition | t | i
> -----------+--------------------------------------+---
> 1 | 84e2c963-4ef9-11e9-b580-f0def1d0755e | 3
> 1 | 84e2c963-4ef9-11e9-b581-f0def1d0755e | 4
> 1 | 84e2c963-4ef9-11e9-b582-f0def1d0755e | 5
> 1 | 84e2c963-4ef9-11e9-b57e-f0def1d0755e | 1
> 1 | 84e2c963-4ef9-11e9-b57f-f0def1d0755e | 2
>
> (5 rows)
> cqlsh:test>
> {noformat}
> The expected behavior is that the rows are returned in the same order as they were inserted (we inserted them with their clustering key in an ascending order). Instead, the order "wraps" in the middle.
> This issue only arises when the 9th octet (clock_seq_low) in the uuid goes from 7f to 80. A guess would be that the comparison is implemented as a signed integer instead of an unsigned integer, as 0x7f = 127 and 0x80 = -128. According to the RFC, the field should be treated as an unsigned integer: [https://tools.ietf.org/html/rfc4122#section-4.1.2]
> Changing the field from a timeuuid to a uuid gives the expected correct behavior:
> {noformat}
> cqlsh:test> CREATE TABLE t (
> ... partition int,
> ... t uuid,
> ... i int,
> ...
> ... PRIMARY KEY(partition, t)
> ... )
> ... WITH CLUSTERING ORDER BY(t ASC);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b57e-f0def1d0755e, 1);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b57f-f0def1d0755e, 2);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b580-f0def1d0755e, 3);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b581-f0def1d0755e, 4);
> cqlsh:test> INSERT INTO t(partition, t, i) VALUES(1, 84e2c963-4ef9-11e9-b582-f0def1d0755e, 5);
> cqlsh:test> SELECT * FROM t WHERE partition = 1 ORDER BY t ASC;
>
> partition | t | i
> -----------+--------------------------------------+---
> 1 | 84e2c963-4ef9-11e9-b57e-f0def1d0755e | 1
> 1 | 84e2c963-4ef9-11e9-b57f-f0def1d0755e | 2
> 1 | 84e2c963-4ef9-11e9-b580-f0def1d0755e | 3
> 1 | 84e2c963-4ef9-11e9-b581-f0def1d0755e | 4
> 1 | 84e2c963-4ef9-11e9-b582-f0def1d0755e | 5
>
> (5 rows)
> cqlsh:test>{noformat}
>
>
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