324 DB2 UDB ESE V8 Performance Guide for High Performance OLTP and BI
memory) to be made available for backup, which may not be viable in some
environments.
4.7.3 Best practices
We recommend the following best practices to achieve superior restore
performance; these are very similar to the recommendations made for the backup
command.
1. Increase the restore buffer size
The
BUFFER buffer-size parameter specifies the size in 4 KB pages to be used
in restoring the backup image (the default value is 1024).
The restore buffer size should be an integer multiple of the backup buffer size
specified during the backup operation.
To determine the buffer size used in creating the backup image, issue the
following command:
db2ckbkp -h <filename of backup image>
Example 4-1 shows the sample output of such a command.
Example 4-1 Determining backup buffer size
db2ckbkp -h SAMPLE2.0.krodger.NODE0000.CATN0000.19990818122909.001
=====================
MEDIA HEADER REACHED:
=====================
Server Database Name --SAMPLE2
Server Database Alias --SAMPLE2
Client Database Alias --SAMPLE2
Timestamp --19990818122909
Database Partition Number --0
Instance --krodger
Sequence Number --1
Release ID --900
Database Seed --65E0B395
DB Comment ’s Codepage (Volume)--0
Note: The util_heap_sz database configuration parameter specifies the
maximum database shared memory available for use by the backup, restore
and load utilities. An insufficient
util_heap_sz specification may prevent
concurrent execution of these utilities.
Note: If an incorrect buffer size is specified, the buffers allocated will be the
smallest acceptable size.
Chapter 4. Command and utility considerations 325
DB Comment (Volume)--
DB Comment ’s Codepage (System)--0
DB Comment (System)--
Authentication Value --255
Backup Mode --0
Backup Type --0
Backup Gran.--0
Status Flags --11
System Cats inc --1
Catalog Database Partition No.--0
DB Codeset --ISO8859-1
DB Territory --
Backup Buffer Size --4194304
Number of Sessions --1
Platform --0
The proper image file name would be:
SAMPLE2.0.krodger.NODE0000.CATN0000.19990818122909.001
[1 ]Buffers processed:####
Image Verification Complete -successful.
2. Increase the number of buffers.
Incrementally increase the number of restore buffers until no performance
improvements are observed (this is a trial and error exercise).
3. Increase the value of the
PARALLELISM parameter.
This parameter defines the number of buffer manipulators (BM) that will be
used to write to the database/table space during the restore operation. The
default is 1.
Each BM is assigned to a specific table space. When it finishes restoring this
table space, it requests another. Each BM incurs both memory and CPU
overhead.
During restore, it is reasonable to assume that pages can be written to table
space containers faster than they can be read from the backup images
sources. As long as this assumption is true, then a parallelism value that is
less than the number of sources may cause the backup image I/O to halt
temporarily (a parallelism value that is greater than the number of backup
image sources offers diminishing returns at some small cost). Choose a
parallelism value equal to the number of backup image sources.
4. No throttling
The default is no throttling.

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