Glossary
P
package
A control structure produced during
program preparation that is used to execute SQL statements.
packet
In data communication, a sequence of
binary digits, including data and control signals, that is transmitted and
switched as a composite whole.
page
A block of storage within a table or index
whose size is 4096 bytes (4 K).
parallel I/O
Refers to the process of reading from or
writing to two or more I/O devices at the same time to reduce response time.
parallelism
The ability to perform multiple database
operations at the same time (in parallel). See inter-partition parallelism,
intra-partition parallelism, and parallel I/O.
parallel session
In SNA, two or more concurrently active
sessions between the same two logical units (LUs). Each session can have
different session parameters. Contrast with session.
parameterized data type
A data type that can be defined with a
specific length, scale, or precision. These are the string and decimal data
types.
parameter marker
A question mark (?) that appears in a
statement string of a dynamic SQL statement. The question mark can appear
where a host variable could appear if the statement string was a static SQL
statement.
parent key
A primary key or unique key that is used
in a referential constraint. The values of a parent key determine the valid
values of the foreign key in the constraint.
parent row
A row that has at least one dependent row.
parent table
A table that is a parent in at least one
referential constraint.
partition compatible join
A join where all of the rows that are
joined reside in the same database partition.
partitioned database
A database with two or more database partitions. Data in user tables can
be located in one or more database partitions. When a table is on multiple
partitions, some of its rows are stored in one partition and others are stored
in other partitions. See database partition.
partitioning function
A function that takes a partitioning key
value of a row as input and produces a partition number as output.
partitioning key
(1) An ordered set of one or more columns in a
given table. For each row in the table, the values in the partitioning key
columns are used to determine on which database partition the row belongs.
(2) In replication, an ordered set of one or
more columns in a given table. For each row in the source table, the values in
the partitioning key columns are used to determine in which target table the
row belongs.
partitioning map
A vector of partition numbers that maps a
partitioning map index to database partitions in the nodegroup.
partitioning map index
A number assigned to a hash partition or
range partition.
partner logical unit (LU)
In SNA, the remote participant in a
session.
peer-to-peer communication
Communication between two SNA logical
units (LUs) that is not managed by a host; commonly used when referring to LU
6.2 nodes.
performance metrics
A collection of all performance variables
belonging to the same database object.
Performance Monitor
A tool that lets database administrators
use a graphical interface to monitor the performance of a DB2 system for
tuning purposes. The tasks provided by this tool can be accessed from the
Control Center.
performance snapshot
Performance data for a set of database
objects that is retrieved from the database manager at a point in time.
performance variable
A statistic derived from performance data
obtained from the database manager. The expression for this variable can be
user-defined.
performance variable profile
A flat file that contains definitions of
performance variables. This file can be edited, copied, and shared. Different
profiles can be used by the same Snapshot Monitor so that different
calculations can be performed.
phantom row
A table row that can be read by
application processes that are executing with any isolation level except
repeatable read. When an application process issues the same query multiple
times within a single unit of work, additional rows can appear between queries
because of the data being inserted and committed by application processes that
are running concurrently.
physical unit
The component that manages and monitors
the resources (such as attached links and adjacent link stations) associated
with a node, as requested by an SSCP through an SSCP-PU session. An SSCP
activates a session with the PU in order to indirectly manage, through PU,
resources of the node such as attached links. This term applies to types 2.0,
4, and 5 nodes only. See also control point.
point-in-time table
A type of target table whose content
matches all or part of a source table, with an added system column that
identifies the approximate time when the particular row was inserted or
updated at the source system.
point of consistency
A point in time when all the recoverable
data a program accesses is consistent. The point of consistency occurs when
updates, inserts, and deletions are either committed to the physical database
or rolled back. Synonym for commit point and sync point. See also rollback.
precision
In numeric data types, the total number of
binary or decimal digits excluding the sign.
precompile
To process programs containing SQL
statements before they are compiled. SQL statements are replaced with
statements that will be recognized by the host language compiler. The output
from a precompile includes source code that can be submitted to the compiler
and used in the bind process.
predicate
An element of a search condition that
expresses or implies a comparison operation.
prefetch
To read data ahead of, and in anticipation
of, its use.
prepare
To convert an SQL statement from text form
to an executable form, by submitting it to the SQL compiler.
primary key
A unique key that is part of the
definition of a table. A primary key is the default parent key of a
referential constraint definition.
primary log
A set of one or more log files used to
record changes to a database. Storage for these files is allocated in advance.
Contrast with secondary log.
privilege
The right to access a specific database
object in a specific way. These rights are controlled by users with SYSADM
(system administrator) authority or DBADM (database administrator) authority
or by creators of objects. Privileges include rights such as creating,
deleting, and selecting data from tables.
procedure
Synonym for stored procedure.
protocol.ini
A file that contains LAN configuration and
binding information for all the protocol and medium access control (MAC)
system modules.
PU
Physical unit.
public authority
The authority for an object granted to all
users.
PU type
In SNA, the classification of a physical
unit (PU) according to the type of node on which it resides.
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