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https://issues.apache.org/jira/browse/DERBY-6852?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15331246#comment-15331246
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Danoja Dias edited comment on DERBY-6852 at 6/15/16 7:03 AM:
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I looked in to the code and then I found in sequenceGenerator.java this feature
is already implemented there.
if ( overflowed( _currentValue, nextValue ) )
{
// Take this generator offline if we've wrapped around but cycling
really isn't allowed.
if ( !_CAN_CYCLE )
{
markExhausted( retval );
return;
}
// Otherwise, cycling is allowed.
nextValue = _RESTART_VALUE;
}
I need to find how _CAN_CYCLE variable changes. Here if cycling is allowed,
nextValue is _RESTART_VALUE that is the value we give to start the identity
column when table is created.
I think it must be the minimum value to start, not the value we give when table
is created.
was (Author: dnj):
I looked in to the code and then I found in sequenceGenerator.java this feature
is already implemented there.
if ( overflowed( _currentValue, nextValue ) )
{
// Take this generator offline if we've wrapped around but cycling
really isn't allowed.
if ( !_CAN_CYCLE )
{
markExhausted( retval );
return;
}
// Otherwise, cycling is allowed.
nextValue = _RESTART_VALUE;
}
I need to find how _CAN_CYCLE variable changes. Here if cycling is allowed,
nextValue is _RESTART_VALUE that is the value we give to start the identity
column.
I think it must be the minimum value to start.
> Allow identity columns to cycle (as defined in SQL:2003)
> --------------------------------------------------------
>
> Key: DERBY-6852
> URL: https://issues.apache.org/jira/browse/DERBY-6852
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Peter Hansson
>
> Currently when an IDENTITY column reaches its maximum value it will produce
> an error.
> For tables that are used as 'transaction logs' or 'event logs' it often makes
> sense to let the table automatically start over with the first identity value
> again when the max is reached. This would be similar to the CYCLE option on
> Oracle's SEQUENCE and as defined in SQL:2003. And Derby is probably used
> quite often for this purpose, I guess, perhaps even more than other RDBMSs.
> At the moment every developer have to program their own logic for this.
> I propose to introduce the CYCLE option.
> The idea of CYCLE is based on the assumption that there's been a prior
> cleanup in the table rows so that it will be possible to re-use ids that have
> been used previously. If that is not the case - and a rollover happens - then
> a duplicate value error will occur. In this sense it can be argued that the
> CYCLE option will trade a _certain_ error for a _potential_ error. Most Derby
> users would possibly gladly accept such a bargain. In other words: This
> option will greatly enhance the usability of IDENTITY columns.
> The current implementation of IDENTITY columns SQL grammar in Derby is a
> subset of the SQL:2003 standard which is the first of the SQL standards to
> define IDENTITY columns. Interestingly the standard also defines the CYCLE
> option but this was never implemented in Derby. Also see [SQL-99 and SQL-2003
> features mapped to Derby|https://wiki.apache.org/db-derby/SQLvsDerbyFeatures]
> (scroll to T174).
> In other words: The proposal is simply to implement CYCLE as defined in
> SQL:2003.
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