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Bryan Pendleton edited comment on DERBY-6977 at 11/11/17 4:02 AM:
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Cool! So the problem arises if you create two different sequences within the 
same millisecond? Or tenth of a millisecond? Or hundredth? 

I read through your patch and it looks nice and clean to me. +1 to commit.

I guess that, once we generate the sequence name, it is just a string?

So, if we change the name generator, we have no upgrade issues?




was (Author: bryanpendleton):
Wow it's crazy that we never saw this before.

I read through your patch and it looks nice and clean to me. +1 to commit.

I guess that, once we generate the sequence name, it is just a string?

So, if we change the name generator, we have no upgrade issues?



> Autogenerated index name occasionally generates a name which already exists
> ---------------------------------------------------------------------------
>
>                 Key: DERBY-6977
>                 URL: https://issues.apache.org/jira/browse/DERBY-6977
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions: 10.13.1.1
>            Reporter: Trejkaz
>         Attachments: derby-6977-01-aa-useUUID.diff
>
>
> This has been happening for as long as I can remember, but v10.13.1.1 is the 
> version we're currently at and I still see builds fail at random due to this.
> In a migration, we execute this statement:
> {noformat}
> CREATE TABLE GuidMappingCache (
>     guidhigh  BIGINT NOT NULL,
>     guidlow BIGINT NOT NULL,
>     luceneid INTEGER NOT NULL,
>     PRIMARY KEY (guidhigh, guidlow)
> )
> {noformat}
> This randomly fails with the following sort of error:
> {noformat}
> Caused by: java.sql.SQLException: Index 'SQL171110050418720' already exists 
> in Schema 'APP'.
>       at 
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
>       at org.apache.derby.impl.jdbc.Util.generateCsSQLException(Unknown 
> Source)
>       at 
> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown 
> Source)
>       at 
> org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown 
> Source)
>       at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown 
> Source)
>       at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown 
> Source)
>       at org.apache.derby.impl.jdbc.EmbedStatement.executeStatement(Unknown 
> Source)
>       at org.apache.derby.impl.jdbc.EmbedStatement.execute(Unknown Source)
>       at org.apache.derby.impl.jdbc.EmbedStatement.execute(Unknown Source)
>       at OurCode.execute(...)
> Caused by: ERROR X0Y32: Index 'SQL171110050418720' already exists in Schema 
> 'APP'.
>       at org.apache.derby.iapi.error.StandardException.newException(Unknown 
> Source)
>       at org.apache.derby.iapi.error.StandardException.newException(Unknown 
> Source)
>       at 
> org.apache.derby.impl.sql.catalog.DataDictionaryImpl.duplicateDescriptorException(Unknown
>  Source)
>       at 
> org.apache.derby.impl.sql.catalog.DataDictionaryImpl.addDescriptor(Unknown 
> Source)
>       at 
> org.apache.derby.impl.sql.execute.CreateIndexConstantAction.executeConstantAction(Unknown
>  Source)
>       at 
> org.apache.derby.impl.sql.execute.CreateConstraintConstantAction.executeConstantAction(Unknown
>  Source)
>       at 
> org.apache.derby.impl.sql.execute.CreateTableConstantAction.executeConstantAction(Unknown
>  Source)
>       at org.apache.derby.impl.sql.execute.MiscResultSet.open(Unknown Source)
>       at 
> org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(Unknown Source)
>       at org.apache.derby.impl.sql.GenericPreparedStatement.execute(Unknown 
> Source)
>       ... 37 more
> {noformat}
> The last time someone was looking into this, it was somehow very reproducible 
> for them but not for anyone else. I'm now seeing it occasionally on tests on 
> our build farm. As usual, no matter how many times I run the test here, I 
> can't get the same failure to occur.
> How is this value being generated?



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