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https://issues.apache.org/jira/browse/DERBY-3097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12597770#action_12597770
]
Bryan Pendleton commented on DERBY-3097:
----------------------------------------
Regarding my 7-Oct-2007 request for more information on Beetle 4880, Myrna van
Lunteren
posted the following to the derby-dev mailing list:
------------
NEST_THIS definition:
public static int NEST_THIS( int returnValue,
String statement1 )
throws SQLException, StandardException
{
Connection conn = getCurrentConnection();
PreparedStatement ps = conn.prepareStatement( statement1 );
ps.execute();
return returnValue;
}
ij> create table L_1
(
pk int primary key,
s1 int,
b int,
s2 int,
s3 int
);
0 rows inserted/updated/deleted
ij> create unique btree index L_1_UNIQUE on L_1( s1, s2, s3 );
0 rows inserted/updated/deleted
ij> insert into L_1 ( pk, s1 ) values
( -16, NEST_THIS( 103, 'delete from L_1 properties index=null
where s2 = 103 and s1 =
NEST_THIS( 103, ''insert into L_1 ( pk, s1, s2, s3 ) values
( -18, 3, 1, 1 ), ( -19, 403, 403, 403 )'' )' ) );
-------------------------------
The info further indicates that at one time, this code caused a deadlock.
The notes say: "Consider a query like: select * from t1, t2 where
t2.c1 = MyClass::myMethod(t1.c1). Since the method call's arguments
have no local reference to t2, and the predicate is pushed down as a
qualifier, we should be able to deem it as scan-invariant and evaluate
it once per outer row, so all together row_count(t1) number of times.
And we should evaluate it outside the store, before a heap page is
latched."
I've not tried this code out; not sure the syntax even works in Derby.
I hope it helps.
> Unnecessary if statement can be removed from BaseActivation.getColumnFromNow
> ----------------------------------------------------------------------------
>
> Key: DERBY-3097
> URL: https://issues.apache.org/jira/browse/DERBY-3097
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.4.1.3
> Reporter: Bryan Pendleton
> Assignee: Bryan Pendleton
> Priority: Minor
> Attachments: checkNumOpens.diff
>
>
> In BaseActivation.java there is the following code:
> protected final DataValueDescriptor getColumnFromRow(int rsNumber, int colId)
> throws StandardException {
> if( row[rsNumber] == null)
> {
> /* This actually happens. NoPutResultSetImpl.clearOrderableCache
> attempts to prefetch invariant values
> * into a cache. This fails in some deeply nested joins. See
> Beetle 4736 and 4880.
> */
> return null;
> }
> return row[rsNumber].getColumn(colId);
> }
> During the investigation of DERBY-3033, I came to the conclusion that this
> "if" statement is no longer necessary, and in fact is counter-productive, for
> it makes diagnosing other problems harder by delaying the point at which data
> structure problems are exposed as errors in the code.
> This JIRA issue requests that this code be evaluated, to determine whether or
> not it truly is necessary, and, if it is not necessary, suggests that it
> should be removed, to result in simpler, clearer code.
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