Specifies an optional number of extra buffers to be allocated
for navigating an index file.
Valid in: |
configuration file, SAS invocation, OPTIONS
statement, SAS System Options window
|
Category: |
Files: SAS Files
|
PROC OPTIONS GROUP= |
SASFILES
|
Default: |
0
|
IBUFNO=n | nK | nM | nG | nT |hexX | MIN |
MAX
|
- n | nK | nM |
nG
| nT
-
specifies the number of extra index buffers to be allocated
in multiples of 1 (bytes); 1,024 (kilobytes); 1,048,576 (megabytes); 1,073,741,824
(gigabytes); or 1,099,511,627,776 (terabytes). For example, a value of 8 specifies eight buffers, and a value of 3k specifies 3,072
buffers.
Restriction: |
Maximum value is 10,000. |
- hexX
-
specifies the number of extra index buffers as a hexadecimal
value. You must specify the value beginning with a number (0-9), followed
by an X. For example, the value 2dx specifies
45 buffers.
- MIN
-
sets the number of extra index buffers to 0. This is the
default.
- MAX
-
sets the maximum number of extra index buffers to 10,000.
An index is an optional SAS file that you can create for
a SAS data file in order to provide direct access to specific observations.
The index file consists of entries that are organized into hierarchical levels,
such as a tree structure, and connected by pointers. When an index is used
to process a request, such as for WHERE processing, SAS does a binary search
on the index file and positions the index to the first entry that contains
a qualified value. SAS uses the value's identifier to directly access the
observation that contains the value. SAS requires memory for buffers when
an index is actually used. The buffers are not required unless SAS uses the
index, but they must be allocated in preparation for the index that is being
used.
SAS automatically allocates a minimal number of buffers in order to
navigate the index file. Typically, you do not need to specify extra buffers.
However, using IBUFNO= to specify extra buffers could improve execution time
by limiting the number of input/output operations that are required for a
particular index file. However, the improvement in execution time comes at
the expense of increased memory consumption.
Note: Whereas too few buffers allocated to the index file decrease
performance, over allocation of index buffers creates performance
problems as well. Experimentation is the best way to determine the optimal
number of index buffers. For example, experiment with ibufno=3, then ibufno=4, and so on,
until you find the least number of buffers that produces satisfactory performance
results. ![[cautionend]](../../../../common/63294/HTML/default/images/cautend.gif)
|
"Understanding SAS Indexes" in
SAS Language Reference: Concepts. |
|
System Option:
|
Copyright © 2011 by SAS Institute Inc., Cary, NC, USA. All rights reserved.