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From "Bernt M. Johnsen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2591) DataDictionaryImpl.getSystemSQLName() may generate duplicates
Date Wed, 25 Apr 2007 14:15:15 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12491657
] 

Bernt M. Johnsen commented on DERBY-2591:
-----------------------------------------

BTW: Since only two digits is used for YY, there is also a risk for collisions in a 100-year
cycle (remember Y2K anyone?). This is not fixed by the attached patch.

> DataDictionaryImpl.getSystemSQLName() may generate duplicates
> -------------------------------------------------------------
>
>                 Key: DERBY-2591
>                 URL: https://issues.apache.org/jira/browse/DERBY-2591
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>            Reporter: Bernt M. Johnsen
>         Assigned To: Bernt M. Johnsen
>         Attachments: DERBY-2591.diff
>
>
> DataDictionaryImpl.getSystemSQLName() may generates names on the form SQLYYMMDDHHMMSSmmN
where mm is in 10 milliseconds and N is number to avoid collisions with 10 milliseconds. The
name was probably generated this way to fit into the 18 caharcter limit of constraint names
in older derby versions. However, if a getSystemSQLName() is called 12 hours after a call
on the same date (e.g at 01:00:00 and 13:00:00), which is unlikely but not very unlikely,
a duplicate name is generated, since the HH-part is filled by the call
> 				generatedSystemSQLName.append(twoDigits(calendarForLastSystemSQLName.get(Calendar.HOUR)));
> and Calendar.HOUR implementes the pretty stupid idea that there are only 12 hours. It
was definitely Calendar.HOUR_OF_DAY which gives you the hour for a 24-hour clock that should
have been used. 

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