Glossary

block

a group of observations in a data set. By using blocks, thread-enabled applications can read, write, and process the observations faster than if they are delivered as individual observations.

compound WHERE expression

a WHERE expression that contains more than one operator, as in WHERE X=1 and Y>3. See also WHERE expression.

controller

a computer component that manages the interaction between the computer and a peripheral device such as a disk or a RAID. For example, a controller manages data I/O between a CPU and a disk drive. A computer can contain many controllers. A single CPU can command more than one controller, and a single controller can command multiple disks.

CPU-bound application

an application whose performance is constrained by the speed at which computations can be performed on the data. Multiple CPUs and threading technology can alleviate this problem.

data partition

a physical file that contains data and which is part of a collection of physical files that comprise the data component of a SAS Scalable Performance Data Engine data set. See also partition.

I/O-bound application

an application whose performance is constrained by the speed at which data can be delivered for processing. Multiple CPUs, partitioned I/O, threading technology, RAID (redundant array of independent disks) technology, or a combination of these can alleviate this problem.

light-weight process thread

a single-threaded subprocess that is created and controlled independently, usually with operating system calls. Multiple light-weight process threads can be active at one time on symmetric multiprocessing (SMP) hardware or in thread-enabled operating systems.

parallel I/O

a method of input and output that takes advantage of multiple CPUs and multiple controllers, with multiple disks per controller to read or write data in independent threads.

parallel processing

a method of processing that divides a large job into multiple smaller jobs that can be executed simultaneously on multiple CPUs. See also threading.

partition

part or all of a logical file that spans devices or directories. In the SPD Engine, a partition is one physical file. Data files, index files, and metadata files can all be partitioned, resulting in data partitions, index partitions, and metadata partitions, respectively. Partitioning a file can improve performance for very large data sets. See also data partition.

primary path

the location in which SPD Engine metadata files are stored. The other SPD Engine component files (data files and index files) are stored in separate storage paths in order to take advantage of the performance boost of multiple CPUs.

RAID

See redundant array of independent disks.

redundancy

a characteristic of computing systems in which multiple interchangeable components are provided in order to minimize the effects of failures, errors, or both. For example, if data is stored redundantly (in a RAID, for example), then if one disk is lost, the data is still available on another disk. See also redundant array of independent disks.

redundant array of independent disks (RAID)

a type of interleaved storage system that comprises multiple disks to store large amounts of data inexpensively. RAIDs can have several levels. For example, a level-0 RAID combines two or more hard drives into one logical disk drive. Various RAID levels provide different amounts of redundancy and storage capability. Also, because the same data is stored in different places, I/O operations can overlap, which can result in improved performance. See also redundancy.

SAS Scalable Performance Data Engine (SPD Engine)

a SAS engine that organizes data into a streamlined file format, enabling rapid delivery of data to applications. See also parallel I/O, parallel processing.

sasroot

a representation of the name for the directory or folder in which SAS is installed at a site or a computer.

scalability

the ability of a software application to function well and with minimal loss of performance, despite changing computing environments, and despite changes in the volume of computations, users, or data. Scalable software is able to take full advantage of increases in computing capability such as those that are provided by the use of SMP hardware and threaded processing. See also scalable software.

scalable software

software that responds to increased computing capability on SMP hardware in the expected way. For example, if the number of CPUs is increased, the time to solution for a CPU-bound problem decreases by a proportionate amount. And if the throughput of the I/O system is increased, the time to solution for an I/O-bound problem decreases by a proportionate amount.

server scalability

the ability of a server to take advantage of SMP hardware and threaded processing in order to process multiple client requests simultaneously. That is, the increase in computing capacity that SMP hardware provides increases proportionately the number of transactions that can be processed per unit of time. See also symmetric multiprocessing.

SMP

See symmetric multiprocessing.

sort indicator

an attribute of a data file that indicates whether a data set is sorted, how it was sorted, and whether the sort was validated. Specifically, the sort indicator attribute indicates the following information: 1) the BY variable(s) that were used in the sort; 2) the character set that was used for the character variables; 3) the collating sequence of character variables that was used; 4) whether the sort information has been validated. This attribute is stored in the data file descriptor information. Any SAS procedure that requires data to be sorted as a part of its process uses the sort indicator.

spawn

to start a process or a process thread such as a light-weight process thread (LWPT). See also thread.

SPD Engine

See SAS Scalable Performance Data Engine.

SPD Engine data file

the data component of an SPD Engine data set. In contrast to SAS data files, SPD Engine data files contain only data; they do not contain metadata. The SPD Engine does not support data views. See also SPD Engine data set.

SPD Engine data set

a data set created by the SPD Engine that has up to four component files: one for data, one for metadata, and two for any indexes. The minimum number of component files is two: data and metadata. Data is separated from the metadata for SPD Engine file organization.

symmetric multiprocessing (SMP)

a type of hardware and software architecture that can improve the speed of I/O and processing. An SMP machine has multiple CPUs and a thread-enabled operating system. An SMP machine is usually configured with multiple controllers and with multiple disk drives per controller.

thread

the smallest unit of processing that can be scheduled by an operating system.

thread-enabled operating system

an operating system that can coordinate symmetric access by multiple CPUs to a shared main memory space. This coordinated access enables threads from the same process to share data very efficiently.

thread-enabled procedure

a SAS procedure that supports threaded I/O or threaded processing.

threaded I/O

I/O that is performed by multiple threads in order to increase its speed. In order for threaded I/O to improve performance significantly, the application that is performing the I/O must be capable of processing the data rapidly as well. See also I/O-bound application, thread.

threaded processing

processing that is performed in multiple threads in order to improve the speed of CPU-bound applications. See also CPU-bound application, symmetric multiprocessing.

threading

a high-performance technology for either data processing or data I/O in which a task is divided into threads that are executed concurrently on multiple cores on one or more CPUs.

time to solution

the elapsed time that is required for completing a task. Time-to- solution measurements are used to compare the performance of software applications in different computing environments. In other words, they can be used to measure scalability. See also scalability.

WHERE expression

is a syntax string within a WHERE clause that defines the criteria for selecting observations. For example, in a membership database, the expression "WHERE member_type=Senior" returns all senior members. See also compound WHERE expression.