Free Database Archiving Webinar

Attend a free webinar on database archiving on November 28, 2007 at 10:30 am CST.

The webinar, which I will be co-hosting with Bill Baker, will tackle the issue of skyrocketing data volumes in conjunction with increasing governmental regulations that impact the duration of data retention. These dual trends (among several others) conspire to make it difficult to ensure that your organization is in compliance regarding its operational data. As required data retention periods increase it becomes imperative that organizations develop a solid practice for archiving and managing business data from their online operational databases.

Now you may have read about database archiving either in my blogs (Long-Term Data Retention Drives Database Archiving, Data Management Today blog) or elsewhere, but here is a chance to attend a free presentation on the topic to learn all about the trends, troubles, and nuances involved in successfully archiving database data.

I hope you can find the time to attend!

BACKUP and RESTORE SYSTEM [DB2 9 for z/OS]

I am posting today’s blog entry from Athens, Greece as I participate in the European IDUG conference. Good thing I know how to use the Blogger site because when I log in over here in Greece the text on their site is all converted into Greek - and as I'm sure comes as no surprise to anyone, I don't understand Greek!

Anyway, today's post will be about the improvements IBM has made to the BACKUP SYSTEM and RESTORE SYSTEM utilities in DB2 9 for z/OS. And this will be the final entry in this series on Version 9 features discussing utility improvements… it will not be the last in the series on V9 improvements though, just the last one on the utilities.

Also, please keep in mind that these blog posts are meant to deliver a flavor of the new functionality in DB2 9 for z/OS. They will not cover every nuance and detail of what V9 has to offer. With that said, let’s dive into the enhancements to the BACKUP and RESTORE SYSTEM utilities.

Overview

As most of you surely know, BACKUP SYSTEM and RESTORE SYSTEM were are relatively new utilities, added to DB2 as of Version 8. They use disk volume FlashCopy backups and copypool z/OS DFSMShsm V1R5 constructs to copy and restore large volumes of DB2 data. In DB2 V9 these utilities are enhanced to use new functions available with z/OS V1R8 DFSMShsm.

Recovery of Individual Database Objects

In V9, backups produced by BACKUP SYSTEM (aka system level backups) can be used to recover individual table spaces or index spaces. This is helpful because previously you had to recover the entire system, and that is not always what is necessary.

When you wish to recover a subset of a system level backup you will use the RECOVER utility instead of RESTORE SYSTEM. Before your RECOVER jobs can use system level backups you must first set the SYSTEM_LEVEL_BACKUPS DSNZPARM option to YES. This can be set from the DSNTIP6 install panel. If you specify YES then your system-level backups will be considered in object level recoveries (along with your other image copy backups).

If you wish to use your system level backups for individual database object recoveries then you need to make sure that you are copying your indexes (specifying COPY YES).

Why would you want to use your system level backups in this way? Well, doing so should enable you to reduce the frequency with which you are taking conventional image copies. If you take a daily system level backup, then the database objects that you were also backing up on a daily basis may not be required. Of course, you cannot completely forgo all individual image copies because the system level backup timing may not conform to the timing needed for each object based on application requirements, and of course, image copies will still be needed after running utilities like LOAD REPLACE and REORG LOG NO to resolve copy pending situations.

Tape Support for BACKUP SYSTEM

DB2 V9 also delivers the ability for the BACKUP SYSTEM utility to copy the data directly to tape. The new parameters allowing this capability are the DUMP and DUMPONLY options.

The output of the DUMP or DUMPONLY is directed to a DFSMShsm dump class, which specifies the unit type the data will be directed to. Although IBM implemented this change to enable tape support, an SMS dump class is not restricted to tape.

Keep in mind that directing data to tape will have an impact on the speed of your restore. Restoring from tape will not be as fast as restoring from a FlashCopy made to disk. Of course, having your data on tape can help in terms of storage management, disaster recovery and off-site data storage, and long-term data retention. So be aware of these trade-offs before creating system level backups on tape.

Additionally, recognizing that copying data to tape can be time-consuming IBM has added a new keyword, FORCE, to enable a new backup to be started even if a previous DUMP has not yet completed. Of course, FORCE should not be used all the time - - only be used when it is very critical that a new backup be started.

Incremental FlashCopy

And finally, support for incremental copying has been added to FlashCopy. So now you can take a system level backup and then subsequent incremental system level backups. An incremental FlashCopy will copy only the tracks that have changed on the source volume since the last copy was taken. But unlike a typical incremental image copy, the previous content on the volume(s) will be replaced by the new content. That means there is no merging of incrementals required; essentially, the merge is part of the incremental FlashCopy.

I won’t go into all of the gory details here but this new functionality can greatly minimize I/O activity for system level backups.

Summary

So, to sum things up, the ability to work with system level backups becomes easier in V9 because you can recover individual table spaces and indexes from a system level backup without having to restore the entire backup, you can make system level backups directly to tape, and we get the ability to do incremental system level backups. All in all, some nice new features for BACKUP SYSTEM and RESTORE SYSTEM, wouldn't you say?

Improvements to the REORG Utility [DB2 9 for z/OS]

As we continue to wind our way through the multiple improvements that DB2 V9 brings to the IBM utilities, it is time to address the enhancements made to the REORG utility.

Performance

First up, let’s talk about performance improvements. In DB2 9 for z/OS, the REORG utility can unload and reload partitions in parallel. This should result in a nice reduction in elapsed time when you are reorganizing partitioned table spaces. To enable this improvement you will need to code the NOSYSREC keyword or the UNLDDN keyword with a template. Note that NOSYSREC is always used for SHRLEVEL change.

Parallelism will not be enabled if any of the following conditions apply:

• DATAWKnn ddnames are specified in the JCL
• SORTDEVT keyword is not specified
• UTPRINT is allocated to anything other than SYSOUT
• The REBALANCE keyword is used.

Also consider that REORG SHRLEVEL CHANGE can use subtasks during the LOG phase to speed up the processing of log records. Subtasks will be used when unload and reload have been done by partition and there are log records to apply for the partition.

BUILD2 Phase Eliminated in Online REORG

As you probably know, an Online REORG uses shadow data sets. The reorganization is done to the shadows while the data remains available in the primary data sets. When the REORG is done, the shadow data sets are switched to be the primary data sets.

As most DBA know, reorganization by partition can create a long outage when non-partitioned indexes (NPIs) exist on the table. Why is this so? Well, prior to V9, during Online REORG, NPIs had to be updated with the new RIDs for the data of the partition being reorganized during the BUILD2 phase. And that is what typically caused the sometimes significant outage.

With DB2 V9, the BUILD2 phase is eliminated. Instead, the entire NPI will be reorganized and then switched in the SWITCH phase along with all of the other data sets. The only outage is during the SWITCH phase, which will be much, much shorter than the BUILD2 phase outage.

As a result of the elimination of the BUILD2 phase, DB2 will need additional temporary storage for the shadow data sets for each NPI. Additionally, the cost of the REORG will increase because building an entire NPI will consume more CPU than the previous method of updating RIDs in the BUILD2 phase. Finally, you will need to modify any REORG jobs against different partitions that ran in parallel because the entire NPI will be built and then switched.

What about running REORG SHRLEVEL REFERENCE by partition? Well, REORG SHRLEVEL REFERENCE by partition will also rebuild any associated NPIs using shadows. So the same type of concerns apply (more disk storage, additional CPU, no separate jobs in parallel).

Reorganization and LOBs

Finally, as I blogged about before in the posting on LOBS, prior to V9 you could not access LOB data during a REORG. And a REORG did not reclaim physical space from the LOB data set because LOBs were moved within the existing LOB table space. V9 fixes these problems. During a REORG (in V9), the original LOB table space is drained of writers. All LOBs are then extracted from the original data set and inserted into a shadow data set. When this operation is complete, all access to the LOB table space is stopped (the readers are drained) while the original data set is switched with the shadow data set. At this point, full access to the new data set is enabled, and an inline copy is taken to ensure recoverability of data.

Miscellaneous Utility Enhancements [DB2 9 for z/OS]

Today we will continue along with our coverage of new features and functionality oif DB2 9, specifically within the IBM DB2 utilities. Here we will discuss several miscellaneous changes introduced to the IBM DB2 utilities in version 9.

One of these small changes comes to us with the DSN1LOGP utility. The utility will now detect possible erroneous recovery information. For example, consider a situation where you specify a range of log records to print but the entire range is no longer recorded in the BSDS. This can happen if your archive logs have rolled off. Prior to DB2 V9 DSN1LOGP would have just merrily printed the records for you. But because this can be confusing and c ould lead you to recoverying improperly, V9 will detect this situation, produce a RC 4 and the DSN1224I error message Indicating logs could not be found.

Another nice new utility-related enhancement made to DB2 9 for z/OS is that the DB2 Utilities Panel within DB2I adds an option for you to specify the SDSNLOAD library. This is useful when there are more than one DB2 subsystems on an LPAR.

DSN1COPY has been enhanced, too. As of DB2 9 for z/OS, running DSN1COPY RESET to copy a compressed table space from a non-data sharing DB2 subsystem to another non-data sharing subsystem will copy the specified data and reset the PGLOGRBA of each page and the dictionary version. In V7 and V8 the dictionary version was not reset (instead, you had to REORG the copied table space with KEEPDICTIONARY=NO in the target subsystem). This was not an issue for data sharing because the LRSN is used instead of an RBA.

Keep an eye out for future editions of this blog where we will go over the V9 changes for REORG and the BACKUP and RESTORE SYSTEM utilities.

RECOVER Improvements [DB2 9 for z/OS]

Our examination of the new utility functionality in DB2 9 for z/OS continues today as we uncover what’s new with the IBM RECOVER utility.

Point-In-Time Consistency

The most significant enhancement centers on recovering to a point-in-time (PIT) with consistency. As any DBA who has ever been charged with recovering an operational database to a prior PIT knows, it can be challenging to accomplish. Of course, if you have a usable QUIESCE point then point in time recovery is easy. But that means you’d have to have planned ahead of time and taken a QUIESCE, which is not always possible with heavy 24x7 workloads.

Well, DB2 V9 offers some relief because the IBM RECOVER utility is enhanced to automatically identify uncommitted work at the PIT to which you are recovering. After detecting the uncommitted work DB2 will rollback any changes made to the database objects that are being recovered. This means that anything that is being recovered will be in a transactionally consistent state. Of course, you still have to make sure that all of the appropriate objects are participating in the recovery.

This works with for PIT recoveries executed with either the TOLOGPOINT or TORBA keywords only. To accomplish this two new phases are added after the LOGAPPLY phase: LOGSCR and LOGUNDO.

The LOGSCR phase runs for each DB2 member with an active unit of recovery (UR). If no UR was active then this phase will be skipped. During the LOGCSR phase, all active and incomplete URs are identified. This includes URs that were:

• INFLIGHT
• INABORT
• INDOUBT
• POSTPONED ABORT

If any URs were found, the LOGUNDO phase runs. This is where RECOVER backs out
the changes made on recovered objects by active URs. In a data sharing environment, this
will be done one member at a time.

Additional Information on the Progress of Your Recovery

Another improvement made to the IBM RECOVER utility in V9 is the ability to gather more information about the progress of the recovery. Any DBA who has been tasked with sitting around and monitoring recoveries what the DISPLAY command to show accurate, up-to-date, and appropriate information about the status of the recovery.

Well, DB2 V9 enhances the -DISPLAY UTILITY command to provide additional information during the LOGAPPLY phase. DISPLAY now will show the range of the log that needs to be applied, for the database objects that are being recovered. It will also show the progress up to the last commit, as well as the elapsed time since the start of the log apply phase of the recovery.

This information will assist the DBA in determining how long it will take for the recovery job to successfully complete.

Using an Earlier Image Copy

One final enhancement made to the RECOVER utility in V9 gives the DBA control to get DB2 to recover using an earlier image copy. This is accomplished by specifying a point in the log before which DB2 must select an image copy for the recovery.

This technique can be particularly helpful when the most recent image copy is damaged or somehow unusable. You can use an earlier copy by providing an RBA/LRSN value to the new RESTOREBEFORE parameter that is at a point on the log prior to when the unusable image copy was taken.