IBM Db2 Analytics Accelerator for z/OS Version 7.1.8 Release Notes

Find information about new functions here.

Click here for the list of APARs.

• Data on an accelerator might be uncompressed or the compression rate is lower than the rate used by Db2 for z/OS.
• 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.
• The table size shown for each table in the Accelerator view of the IBM Db2 Analytics Accelerator Studio is too large.
• 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.
• Before running SYSPROC.ACCEL_ALTER_TABLES on partitioned tables that are updated incrementally, run SYSPROC.ACCEL_LOAD_TABLES to avoid a loss of table rows on the accelerator.
• After a reactivation of the SSC LPAR for Db2 Analytics Accelerator on IBM Z, the Accelerator appliance installation status on the Accelerator page of the Appliance Installer shows a status of  failed although the appliance is fully functional (all component status indicators are green).
• After clicking "Apply" in IBM Data Studio to start a software update, no pop-up window is displayed to indicate that the update has started.

The SYSPROC.ACCEL_LOAD_TABLES stored procedure behaves differently if automatic change detection is enabled.
Before version 7.1.7, a load job with a setting of detectChanges=“DATA” sometimes did not capture the changes in all partitions if the lock mode NONE had been used for the previous load.
This was fixed with version 7.1.7.

The new behavior:
If you use lock mode NONE and detectChanges=“DATA”, it can happen that more changes are detected than are actually transferred to the accelerator. This is caused by the SKIP LOCKED DATA option, which is used implicitly by the Db2 Unload Utility. If parts of the data were locked by other processes, then this data is ignored and not unloaded to the accelerator.

To ensure that all changes are finally transferred, a partition in an accelerator-shadow table is always fully reloaded if it was previously loaded with lock mode NONE and detectChanges=“DATA”. A reload is started even if the partition had no further changes since then.

If you plan to install or upgrade IBM Db2 Analytics Accelerator, please contact IBM support by opening a PMR first.

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.

Accelerator-only tables

• Multi-row inserts fail if rows contain NULL values to be inserted in columns of data type BINARY or VARBINARY.

  Recommendation
  Do not use the multi-row insert method under these conditions.

• An INSERT with subSELECT where the top level SELECT has an ORDER BY will fail with DSNT408I SQLCODE = -901, ERROR: UNSUCCESSFUL EXECUTION CAUSED BY A SYSTEM.

  Recommendation
  Remove the ORDER BY clause if it is not needed.

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 submit queries to a newly paired accelerator.

• The query result is "undefined" under the following conditions:
  (a) A query contains a CAST AS TIMESTAMP expression and a TIMESTAMP() function call on a CHAR(14) column.
  (b) The CHAR(14) column contains timestamp values in the format yyyyddmmHHMMSS.

  Recommendation
  The problem will be fixed in a later release.

• A query running during a partial reload of an incrementally updated table might be unable to access the new partitions.

  Recommendation
  Re-run the query after the partial reload has finished.

• In version 7.1.8, SQL queries that return a large result set might run slower than in previous versions.

  Recommendation
  Contact IBM support to help you tweak your spill queue settings.

Loading tables

• 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.

• The load operation fails with message AQT20113E: The operation RECEIVE, which was supposed to transfer 4 bytes on TCP/IP socket 2, failed because the connection to the IP address of the remote machine 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 from the IBM Db2 Analytics Accelerator Console. If the problem persists, open a service request and provide a trace file.

• If you run SYSPROC.ACCEL_LOAD_TABLES with lock mode "TABLESET", the operation might fail and return an AQT10071E error.

  Recommendation
  Cancel the previous load and re-run the load operation.

• The load performance degrades as the number of table loads or table removals increases.

  Recommendation
  Suspend load jobs and table removals for 1 minute.

Incremental updates

• The time needed to reload a set of incrementally updated tables increases as well as the replication latency.

  Recommendation
  Pause after each reload, as this allows the system to come back to normal throughput rates and latency levels.

Monitoring

• The values of the monitoring counter Q8STTMUD are to high, for example 0.18E+20.

  Recommendation
  Ignore the high value. It will be corrected during the next collection of statistics.

• The monitoring values of the Q8STCQL, Q8STCQLS, and Q8STQUEW metrics might be displayed incorrectly.

Tracing

• The information collected by the apdiag tool is not included in the trace archive of the appliance.

  Recommendation
  Contact IBM L3 support and ask if this information is really needed.

Miscellaneous

• 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, SQLSTATE=40001, and rc=68.

  Recommendation
  Reduce the task diversity of parallel jobs if you process big table sets with more than 100 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.

• DSNX881I messages are not written to Db2 V12 SYSLOGs. The problem occurs after installing patch PH00574.

  Recommendation
  Apply APAR PH10672.

• Error when removing multiple tables in parallel. The following error message is diep"AQT20118E: A distributed commit between the stored procedure and the server failed for the following reason: Distributed commit failed while initiator was preparing for commit".

  Recommendation
  Repeat the operation.

Issues specific to IBM Db2 Analytics Accelerator on Z

• Query performance does not meet expectations in connection with large system memories.

  Recommendation
  Ask IBM support for reload recommendations and help with the memory configuration.

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

  Recommendation
  Specify only FICON DASD devices or only FCP storage devices in a single storage pool definition.