IBM Db2 Analytics Accelerator for z/OS Version 7.1.4 Release Notes

General recommendations

• Under a very high system load, the accelerator might appear slow or run into timeouts.

  Recommendation
  Do not run more than 30 load threads in parallel.

Creating accelerator-only tables

• Creating an accelerator-only table fails with a message indicating that the accelerator-only table is not available.

  Recommendation
  Retry the operation.

Queries

• Queries are not routed to a newly paired accelerator if they are submitted shortly after the pairing.
  THE STATEMENT CANNOT BE EXECUTED BY DB2 OR IN THE ACCELERATOR (REASON 13). SQLCODE=-4742, SQLSTATE=560D5, DRIVER ...

  Recommendation
  Wait 30 seconds before you route queries to a newly paired accelerator.

Loading tables

• Data on an accelerator might be uncompressed or the compression rate is lower than the rate used by Db2 for z/OS.

  This will be fixed in an upcoming release.

• After running the REORG utility in Db2 12 for z/OS,  reloads might be wrongly recommended for partitions that have already been loaded on the accelerator.

  Recommendation
  To receive correct reload recommendations, do not use interactive load recommendations and batch job change detection at the same time.

• Add-tables-jobs fail, and no clean-up job is started thereafter.
  When SYSPROC.ACCEL_ADD_TABLES ends abnormally, and is rerun after a few seconds, the following error message is returned:
  "AQT10050E: An internal error occurred on the <accelerator> accelerator: The table <table-name> was already added to the database system with location name <location-name>. The table cannot be added again."
  A subsequent call of SYSPROC.ACCEL_GET_TABLES_INFO returns the message:
  "AQT10134E: The <table-name> table does not exist on the <accelerator> accelerator."
  Recommendation
  Remove the table from the accelerator and add it again.

• Invoking SYSPROC.ACCEL_LOAD_TABLES repeatedly and without interruption on a table partitioned by growth or by range might cause the table to grow. The reason is that data in old, replaced versions of the reloaded partitions cannot be deleted fast enough.
  Recommendation
  If a partitioned accelerator-shadow table grows more quickly than the table usually grows in Db2 for z/OS, try to reload the partitions of that table less often.

• The stored procedure SYSPROC.ACCEL_LOAD_TABLES reports a data size twice as high as the amount that has actually been transferred.

• A load table operation is canceled with the following error message: The current transaction has been rolled back because of a deadlock or timeout. Reason code "68".
  Recommendation
  Restart the load operation.

• If you include a growth-partitioned table in a load request and do not specify any partitions or a value for the detectChanges attribute, the table is not reloaded completely.
  Recommendation
  Add forceFullReload="true" to the table specification.

• The load operation fails with message AQT20113E: Operation RECEIVE, which was supposed to transfer 4 bytes on TCP/IP socket 2, failed because the connection to the remote machine at IP address is unknown and port 0 has been closed unexpectedly. Reason: errno = 1121 (EDC8121I Connection reset.).
  Recommendation
  Repeat the load operation. If the problem reoccurs, restart the accelerator server from the IBM Db2 Analytics Accelerator Console. If the problem persists, open a service request and provide a trace file.

• The load operation fails with error message AQT10050E - An internal error occurred on the 'ACCD01' accelerator: An assertion '( mLastUpdateTimestamp.isSet() || ( not mChangeToken.empty() && mLastReorgTimestamp.isSet() ) )' failed. Additional info: Invalid data change statistics:

  <ChangeStats>
  <Token></Token>
  <LastReorgTimestampInClientTime>1970-01-0100:00:00.000000</LastReorgTimestampInClientTime>
  <LastLoadReplaceTimestampInClientTime>1970-01-0100:00:00.000000</LastLoadReplaceTimestampInClientTime>
  <LastUpdateTimestampInClientTime>1970-01-0100:00:00.000000</LastUpdateTimestampInClientTime>
  </ChangeStats>
  Recommendation
  Run Db2 catalog migration.

   

• The column REFRESH_TIME in SYSACCEL.SYSACCELERATEDTABLES is not updated for a load operation. The following value is shown in the REFRESH_TIME column:
  1970-01-01T00:00:00.000000Z.
  Recommendation
  The issue will be fixed in an upcoming release. In the meantime, run the SYSPROC.ACCEL_GET_TABLES_INFO stored procedure to obtain the correct value.

Incremental updates

• If it takes a long time to reload a set of incrementally updated tables, incremental update processing also takes longer and the replication latency increases. 
  Recommendation
  Pause after each reload, as this allows the system to come back to normal throughput rates and latency levels.
   
• In rare situations, incremental updates stop and the spooled output of CHCPROC shows the following error message:
  CHC7061E Failure in TCP/IP send. The returned errno is ECONNRESET for a value of 54

  Recommendation
  On the Db2 Analytics Accelerator Console, select "Restart Incremental Update processes".

• Network issues or component failures might lead to an interruption of incremental update processes. In such a situation, it can happen that the log reader position, as reported by the CDC capture agent, does not advance anymore. Moreover, the replication counters reported by the SYSPROC.ACCEL_GET_ACCELERATOR_INFO stored procedure do not increase any further.
  Recommendation
  Stop affected incremental update processes. Then restart these.

• If incremental updates are enabled for an accelerator, the start of any new task might fail with an error message like:
  "DRDATCPIPException: A TCP operation timed out on message type 0x0000: Receive message failed after timeout of 10 seconds" is received.

  Recommendation
  Restart the task.

• Incremental updates stop unexpectedly.  If you run the getReplicationEvents function of the SYSPROC.ACCEL_CONTROL_ACCELERATOR stored procedure, the following events are reported:
  Type: Error
  Event ID: 1,475
  Originator: com.datamirror.ts.target.apply.bulkapply.db2.Db2TargetBulkApplyJob
  Time: Oct 15, 2018, 9:55:28 PM
  Message:
  Subscription <subscriptionname> is terminating abnormally.
  
  Type: Error
  Event ID: 6,702
  Originator: com.datamirror.ts.target.apply.bulkapply.ExecuteBulkApplyStatementJob
  Time: Oct 15, 2018, 9:55:28 PM
  Message:
  Mirror bulk apply operation failed.
  A SQL exception has occurred. The SQL error code is '0'. The SQL state is: [null]. The error message is: Mirror bulk apply external table insert error occurred. Actual number of affected rows (...) are not equal to expected number of affected rows (...).

  Recommendation
  Disable replication for the affected tables. Then re-enable replication for these tables and reload them.

• In a mixed version 5/version 7 environment (Capture Agent is shared by a version 5 and a version 7 environment), a replication status of "Error" is reported. A restart of the Capture Agent does not resolve the error state for the version 7 environment.

  Recommendation
  Restart incremental update processes from the Db2 Analytics Accelerator Console.

Miscellaneous

• The accelerator server might crash if it is shut down while asynchronous load operations are running. Symptoms: the server is restarted and a core dump is created.

  Recommendation
  Do not shut down the server from the Db2 Analytics Accelerator Console as long as asynchronous load operations are running. Check this with the List tasks function in IBM Db2 Analytics Accelerator Studio before.

• Under a very high system load caused by the parallel execution of various operations, such as 'Add Tables', 'Remove Tables', and 'Alter Keys', the accelerator might restart unexpectedly, leading to the abortion of running tasks or queries.
  Symptoms are aborted tasks, lock timeout exceptions, or messages with SQL code -911 and SQLSTATE=40001 and rc=68.

  Recommendation
  Reduce the task diversity of parallel jobs if you process big table sets with more than 10000 tables. For example, do not run 'Alter Keys', 'Add Tables', and 'Remove Tables' operations at the same time. Reduce this to 'Alter Keys' and 'Add Tables' jobs or any other combination of just two different tasks.
  If a query failed, rerun the query.

• Under a high system load with a high memory usage, the database engine of the accelerator might be restarted automatically, which leads to the abortion of running queries.

  Recommendation
  Restart the aborted tasks and queries.

• After restarting an accelerator from the Db2 Analytics Accelerator Console, network communication with the accelerator is not possible anymore.

  Recommendation
  Restart the accelerator again. This time, use the "Dump additional diagnostics and immediate shutdown" option.

Issues specific to IBM Db2 Analytics Accelerator on IBM Z

Restrictions

• The accelerator does not support a combination of FICON DASD and FCP storage devices within the same storage pool.

  Recommendation
  Use only FICON DASD or only FCP storage devices for a specific storage pool definition.