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The behavior of stored procedure SYSPROC.ACCEL_LOAD_TABLES using automatic change detection was changed.
Prior to maintenance level 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 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.

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.

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 statement and a TIMESTAMP() function call on a CHAR(14) column.
  (b) The CHAR(14) column contains timstamp values in the format yyyyddmmHHMMSS.

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.

• 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.

Incremental updates

• 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.
   

• 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.

Monitoring

• The table size shown for each table in the accelerator view of the IBM Db2 Analytics Accelerator Studio is too large.
• The value for the monitoring counter Q8STTMUD are to high, e.g. 0.18E+20.

  Recommendation
  The high value can be ignored. It will be corrected during the next statistics collection.

• The values for monitoring metrics Q8STCQL, Q8STCQLS, and Q8STQUEW may be displayed incorrectly.

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 and 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.

• 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.

• Before using SYSPROC.ACCEL_ALTER_TABLES with partitioned tables that are replicated, issue a SYSPROC.ACCEL_LOAD_TABLES to avoid lost rows on the accelerator.
• DSNX881I messages are not written to Db2 V12 SYSLOGs. The problem was introduced with PH00574.

  Recommendation
  Apply APAR PH10672.

Issues specific to IBM Db2 Analytics Accelerator on IBM Z

• IDAA on Z query performance below customer expectation in large memory configuration.

  Recommendation
  Contact IBM to get support with memory configuration and reload recommendation.

• 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).

  Recommendation
  You can ignore the wrong status message.

• 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.

Issues specific to IBM Db2 Analytics Accelerator Studio

• After clicking on "Apply" in Datastudio to start a software update operation, no pop up window is displayed to indicate that the software update has been started.

  Recommendation
  If this window does not come up shortly after clicking the button, click the button again.