db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3926) Incorrect ORDER BY caused by index
Date Fri, 10 Apr 2009 19:08:14 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3926?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-3926:
----------------------------------


I don't think tracking down the difference in estimated row count is going to lead you to
the solution to this problem.  For this issue it is key to figure out why the particular plan
chosen in the bug case is wrong.  It may be that the cost of the plan is wrong, but that should
not affect whether any chose plan gives the right result - the cost should never affect that.
 

So again I believe the key thing here is to track down why this plan that has m1 as the outermost
table thinks that this plan does not have to add a sort at the top to get proper
ordering required by order by m0.  My guess is that the bad plan uses the same key for
m1 and m0 which are just ranges on the same table, but has incorrect logic to not see
that it needs m0 using index key as outer most rather than just index key.  

Also don't get confused when the bug is fixed.  My guess is that once the bug is fixed that
the currently chosen plan will get marked correctly as NOT a sort avoidance plan which then
will require an additional sort node which will add to the cost.  This will probably make
it such that the optimizer no longer picks this plan.   

> Incorrect ORDER BY caused by index
> ----------------------------------
>
>                 Key: DERBY-3926
>                 URL: https://issues.apache.org/jira/browse/DERBY-3926
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.1.3.3, 10.2.3.0, 10.3.3.1, 10.4.2.0
>            Reporter: Tars Joris
>         Attachments: derby-reproduce.zip
>
>
> I think I found a bug in Derby that is triggered by an index on a large column: VARCHAR(1024).
I know it  is generally not a good idea to have an index on such a large column.
> I have a table (table2) with a column "value", my query orders on this column but the
result is not sorted. It is sorted if I remove the index on that column.
> The output of the attached script is as follows (results should be ordered on the middle
column):
> ID                  |VALUE        |VALUE
> ----------------------------------------------
> 2147483653          |000002       |21857
> 2147483654          |000003       |21857
> 4294967297          |000001       |21857
> While I would expect:
> ID                  |VALUE        |VALUE
> ----------------------------------------------
> 4294967297          |000001       |21857
> 2147483653          |000002       |21857
> 2147483654          |000003       |21857
> This is the definition:
> CREATE TABLE table1 (id BIGINT NOT NULL, PRIMARY KEY(id));
> CREATE INDEX key1 ON table1(id);
> CREATE TABLE table2 (id BIGINT NOT NULL, name VARCHAR(40) NOT NULL, value VARCHAR(1024),
PRIMARY KEY(id, name));
> CREATE UNIQUE INDEX key2 ON table2(id, name);
> CREATE INDEX key3 ON table2(value);
> This is the query:
> SELECT table1.id, m0.value, m1.value
> FROM table1, table2 m0, table2 m1
> WHERE table1.id=m0.id
> AND m0.name='PageSequenceId'
> AND table1.id=m1.id
> AND m1.name='PostComponentId'
> AND m1.value='21857'
> ORDER BY m0.value;
> The bug can be reproduced by just executing the attached script with the ij-tool.
> Note that the result of the query becomes correct when enough data is changed. This prevented
me from creating a smaller example.
> See the attached file "derby-reproduce.zip" for sysinfo, derby.log and script.sql.
> Michael Segel pointed out:
> "It looks like its hitting the index ordering on id,name from table 2 and is ignoring
the order by clause."

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message