iX V6.5 (30391-90011)

Chapter 3 85

Deﬁning a Database

$CONTROL

Description

The default parameters are

LIST, ROOT, TABLE,

and

NOJUMBO

.Ifno$CONTROL command

is used, the results are the same as if the following $CONTROL command is used:

$CONTROL LIST,ERRORS=100,LINES=60,ROOT,BLOCKMAX=512,TABLE

The parameters can be placed in any order but must be separated by commas.

To specify a jumbo data set, the JUMBO option must be included in the schema before

deﬁning any jumbo data sets. Then any data set whose capacity is greater than 4 GB

automatically becomes a Jumbo data set. If the JUMBO option is not speciﬁed, an error is

generated for the data sets exceeding the 4 GB limit. Use the NOJUMBO option to turn off

the jumbo feature.

DBSTORE does not store jumbo data sets; instead use

TurboSTORE/iX 7x24 True-Online Backup using ONLINE=START or ONLINE=END option.

NOTE

Use only third-party utilities and diagnostic tools that are enhanced to

handle Jumbo data sets.

Selecting the Block Size

The data set records are transferred from the disk to memory in 4096-byte pages in

TurboIMAGE/XL blocks. The block format is described in chapter 10. When you specify a

maximum block size with the $CONTROL command, you should consider:

• Efﬁcient disk space utilization.

• Localizing the block's bit map to the actual data entries within a 4096-byte page.

The Schema Processor determines the number of data records that ﬁt in a block. Note that

DBSCHEMA chooses a block size (less than or equal to the maximum block size) that makes

the best use of disk space, and which can be substantially less than the maximum block

size speciﬁed by $CONTROL BLOCKMAX (or the default of 512 halfwords). If the record size is

greater than 512 halfwords, BLOCKMAX must be set greater than or equal to the record size.

A certain amount of tuning may be necessary to determine the best block size. In general,

the default block size of 512 halfwords yields reasonable performance on TurboIMAGE/XL

and should be changed only when needed.