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Effect of DB2_USE_FAST_PREALLOCATION on a Db2 restore

Question & Answer


Question

What is the effect of using DB2_USE_FAST_PREALLOCATION ON when doing a Db2 restore with the IBM Spectrum Protect API

Answer

Db2 running on AIX, Solaris, or Linux hosts can use the Db2 performance setting DB2_USE_FAST_PREALLOCATION ON when using a VeritasVxFS, JFS2, GPFS™, or ext4 (Linux only) file system. The default setting is ON for VeritasVxFS, JFS2, and GPFS.  Setting the value to OFF would stop the use of this option.

DB2_USE_FAST_PREALLOCATION allows for a much quicker allocation of space when Db2 creates or alters large table spaces. This can be advantageous for restores, as a restore of a large table space to an AIX, Solaris, or Linux host with the setting of ON is able to immediately stream data for the restore without any delays for creation of the DB2 containers.

The documentation for DB2_USE_FAST_PREALLOCATION indicates that this fast pre-allocation comes at the cost of a small amount of extra time spent when the data is written. Thus, the overall time for the restore may not be reduced and can adversely affect the restore in some cases.  Refer to "Diagnosing The Problem" section in the documentation at the link:

https://www.ibm.com/support/pages/how-troubleshoot-and-fix-slow-db2-restore-aix-jfs2-file-system

The documentation for the DB2_USE_FAST_PREALLOCATION is available at the link:


http://www.ibm.com/support/knowledgecenter/SSEPGG_10.5.0/com.ibm.db2.luw.admin.regvars.doc/doc/r0005665.html

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Document Information

Modified date:
14 December 2023

UID

swg21996340

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