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From "James F. Adams (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3093) intermittent transaction failure caused by internal duplicate savepoint name, for tirgger
Date Wed, 17 Oct 2007 00:42:50 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12535384
] 

James F. Adams commented on DERBY-3093:
---------------------------------------

In briefly looking into this issue I noticed that the internal savepoint name is created in
GenericStatementContext's constructor with the following line of code:

		internalSavePointName = "ISSP" + hashCode();

>From the javadoc for Object:

It is not required that if two objects are unequal according to the equals(java.lang.Object)
method, then calling the hashCode method on each of the two objects must produce distinct
integer results. However, the programmer should be aware that producing distinct integer results
for unequal objects may improve the performance of hashtables. 

 As much as is reasonably practical, the hashCode method defined by class Object does return
distinct integers for distinct objects. (This is typically implemented by converting the internal
address of the object into an integer, but this implementation technique is not required by
the JavaTM programming language.)

Another method of creating unique names should be implemented.



> intermittent transaction failure caused by internal duplicate savepoint name, for tirgger
> -----------------------------------------------------------------------------------------
>
>                 Key: DERBY-3093
>                 URL: https://issues.apache.org/jira/browse/DERBY-3093
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions: 10.3.1.4
>         Environment: Java 1.6.0_02
>            Reporter: Jim Newsham
>
> While running our app overnight, performing some intensive database operations (primarily
deletes), we experienced a transaction failure, with error message "A SAVEPOINT with the passed
name already exists in the current transaction".  This failure appears to be very intermittent,
as I've run the same operation successfully for hours and hours without failure.  Some more
information:
> 1.  I see that there are four JIRA issues which report the same message (DERBY-2773,
DERBY-1457, DERBY-2808, DERBY-2804).  I am not sure to what extent if any, the problem I experienced
is related to these issues.
> •	At least three of the above JIRA issues are related to triggers.  Our transaction
failure occurred while performing a delete in a table which has delete triggers.
> •	We aren't using savepoints explicitly.  Of course, it can be seen in the stack trace
that the trigger operation is setting a savepoint.
> •	One of the JIRA issues mentions exceeding maximum depth of nested triggers.  Not
sure what a nested trigger is, but the trigger we are performing should not (in theory) cause
another trigger event.
> 2.  Here's the stack trace:
> Caused by: java.sql.SQLException: A SAVEPOINT with the passed name already exists in
the current transaction.
>         at org.apache.derby.impl.jdbc.SQLExceptionFactory40.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.EmbedPreparedStatement.executeStatement(Unknown
Source)
>         at org.apache.derby.impl.jdbc.EmbedPreparedStatement.executeUpdate(Unknown Source)
>         at com.referentia.sdf.monitor.samplebase.derby.DerbySampleBase$3.perform(DerbySampleBase.java:682)
>         at com.referentia.sdf.monitor.samplebase.derby.DerbySampleBase.performInTransaction(DerbySampleBase.java:2747)
>         ... 7 more
> Caused by: java.sql.SQLException: A SAVEPOINT with the passed name already exists in
the current transaction.
>         at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
>         at org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown
Source)
>         ... 18 more
> Caused by: ERROR 3B501: A SAVEPOINT with the passed name already exists in the current
transaction.
>         at org.apache.derby.iapi.error.StandardException.newException(Unknown Source)
>         at org.apache.derby.impl.store.raw.xact.Xact.setSavePoint(Unknown Source)
>         at org.apache.derby.impl.store.access.RAMTransaction.setSavePoint(Unknown Source)
>         at org.apache.derby.impl.sql.conn.GenericStatementContext.setSavePoint(Unknown
Source)
>         at org.apache.derby.impl.sql.GenericPreparedStatement.execute(Unknown Source)
>         at org.apache.derby.impl.sql.execute.GenericTriggerExecutor.executeSPS(Unknown
Source)
>         at org.apache.derby.impl.sql.execute.RowTriggerExecutor.fireTrigger(Unknown Source)
>         at org.apache.derby.impl.sql.execute.TriggerEventActivator.notifyEvent(Unknown
Source)
>         at org.apache.derby.impl.sql.execute.DeleteResultSet.fireAfterTriggers(Unknown
Source)
>         at org.apache.derby.impl.sql.execute.DeleteResultSet.open(Unknown Source)
>         at org.apache.derby.impl.sql.GenericPreparedStatement.execute(Unknown Source)
>         ... 12 more
> 3.  Here are the relevant tables and triggers. We have different tables for different
"sample" data types  in our application (currently int, long, float, double, Boolean, string).
 I have shown the int_sample table; the other tables are identical but have a different data
type for the value field.  
> Sample records are first class; time records are second class - they only exist to support
sample records.  When there are no remaining sample records for a given time record, the time
record can be removed.  It is the job of the trigger to perform this cleanup:  when a record
is deleted from any of the sample tables, the time record corresponding to *_sample.fk_time_id
is deleted only if there are no remaining records in any of the sample tables which have the
same fk_time_id.  So although there are cascading deletes (deleting a time record deletes
all of its samples), the trigger should not recurse because the trigger only deletes when
there are no associated records.
>  
> create table time (
>   id                  int not null generated always as identity,
>   time                timestamp not null,
>   constraint time_pk primary key (id),
>   constraint time_unique unique (time)
> );
> create table int_sample (
>   fk_band_id          int not null,
>   fk_time_id          int not null,
>   value               int not null,
>   constraint int_sample_pk primary key (fk_band_id, fk_time_id),
>   constraint int_sample_fk_band foreign key (fk_band_id) references band (id) on delete
cascade,
>   constraint int_sample_fk_time foreign key (fk_time_id) references time (id) on delete
cascade
> );
> create trigger cascade_delete_unused_time_for_int_sample_trigger
>   after delete on int_sample
>   referencing old as oldrow
>   for each row
>   delete from time where 
>   time.id = oldrow.fk_time_id
>   and id not in (select fk_time_id from int_sample) 
>   and id not in (select fk_time_id from long_sample) 
>   and id not in (select fk_time_id from float_sample) 
>   and id not in (select fk_time_id from double_sample) 
>   and id not in (select fk_time_id from boolean_sample) 
>   and id not in (select fk_time_id from string_sample);
> 4.  Invocation.  This is very rough pseudocode focusing on the core logic.  In reality,
there's a lot more code, but I'm doing the usual stuff, such as using prepared statements,
and closing all resources when done.  The key thing is that I'm using two statements in a
nested fashion; in the outer statement, I iterate over records in the time table, and in the
inner loop I use a second statement to delete records in one of the sample tables.  I can
provide the actual code if desired.
> deleteSamples(int bandId, String sampleTable, Object someQueryCriteria) {
>   within transaction {
>     create stmt1 iterating over time ids in time table (restricted by someQueryCriteria)
>       for (time_id in stmt1) {
>         PreparedStatement stmt2 = conn.prepareStatement(String.format(
>         "delete from %s where fk_band_id = ? and fk_time_id = ?", sampleTable));
>         set stmt2 parameters and executeUpdate()
>     }
>   }
> }

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