--- /dev/null
+
Glossary
+ This is a list of terms and their meaning in the context of
+
PostgreSQL and relational database
+ systems in general.
+
+
+
+
+ Aggregate Function
+
+ A function that
+ combines (aggregates) multiple input values,
+ for example by counting, averaging or adding,
+ yielding a single output value.
+
+ For more information, see
+ .
+
+
+
+
+
+
+ Analyze (operation)
+
+ The process of collecting statistics from data in
+ tables
+ and other relations
+ to help the query planner
+ to make decisions about how to execute
+ queries.
+
+
+
+
+
+ Analytic Function
+
+
+
+
+ Atomic
+
+ In reference to a datum:
+ the fact that its value that cannot be broken down into smaller
+ components.
+
+
+
+ In reference to a
+ database transaction:
+ see atomicity.
+
+
+
+
+
+ Atomicity
+
+ The property of a transaction
+ that either all its operations complete as a single unit or none do.
+ In addition, if a system failure occurs during the execution of a
+ transaction, no partial results are visible after recovery.
+ This is one of the
ACID properties.
+
+
+
+
+
+ Attribute
+
+ An element with a certain name and data type found within a
+ tuple or
+ table.
+
+
+
+
+
+ Autovacuum
+
+ A set of background processes that routinely perform
+ vacuum
+ and analyze
+ operations.
+
+ For more information, see
+ .
+
+
+
+
+
+ Backend (process)
+
+ Process of an instance
+ which act on behalf of client sessions
+ and handle their requests.
+
+ (Don't confuse this term with the similar terms
+ Background Worker or
+ Background Writer).
+
+
+
+
+
+ Background Worker (process)
+
+ Process within an instance,
+ which runs system- or user-supplied code.
+ Serves as infrastructure for several features in
+ logical replication
+ and parallel queries.
+ In addition, Extensions can add
+ custom background worker processes.
+
+ For more information, see
+ .
+
+
+
+
+
+ Background Writer (process)
+
+ A process that continuously writes dirty pages from
+ shared memory to
+ the file system. It wakes up periodically, but works only for a short
+ period in order to distribute its expensive
I/O+ activity over time to avoid generating larger
+
I/O peaks which could block other processes.
+
+ For more information, see
+ .
+
+
+
+
+
+ Cast
+
+ A conversion of a datum
+ from its current data type to another data type.
+
+ For more information, see
+ .
+
+
+
+
+
+ Catalog
+
+ The
SQL standard uses this term to
+ indicate what is called a
+ database in
+
PostgreSQL's terminology.
+
+ (Don't confuse this term with
+ system catalog).
+
+ For more information, see
+ .
+
+
+
+
+
+ Check Constraint
+
+ A type of constraint
+ defined on a relation
+ which restricts the values allowed in one or more
+ attributes. The
+ check constraint can make reference to any attribute of the same row in
+ the relation, but cannot reference other rows of the same relation or
+ other relations.
+
+ For more information, see
+ .
+
+
+
+
+
+ Checkpointer (process)
+
+ A specialized process responsible for executing checkpoints.
+
+
+
+
+
+ Checkpoint
+
+ A point in the WAL sequence
+ at which it is guaranteed that the heap and index data files have been
+ updated with all information from
+ shared memory
+ modified before that checkpoint;
+ a checkpoint record is written and flushed to WAL
+ to mark that point.
+
+ A checkpoint is also the act of carrying out all the actions that
+ are necessary to reach a checkpoint as defined above.
+ This process is initiated when predefined conditions are met,
+ such as a specified amount of time has passed, or a certain volume
+ of records has been written; or it can be invoked by the user
+ with the command CHECKPOINT.
+
+ For more information, see
+ .
+
+
+
+
+
+ Class (archaic)
+
+
+
+
+ Client (process)
+
+ Any process, possibly remote, that establishes a
+ session
+ by connecting to an
+ instance
+ to interact with a database.
+
+
+
+
+
+ Cluster
+
+ A group of databases plus their
+ global SQL objects. The
+ cluster is managed by exactly one
+ instance. A newly created
+ Cluster will have three databases created automatically. They are
+ template0, template1, and
+ postgres. It is expected that an application will
+ create one or more additional database aside from these three.
+
+ (Don't confuse the
PostgreSQL-specific term
+ Cluster with the SQL
+ command CLUSTER).
+
+
+
+
+
+ Column
+
+ An attribute found in
+ a table or
+ view.
+
+
+
+
+
+ Commit
+
+ The act of finalizing a
+ transaction within
+ the database, which
+ makes it visible to other transactions and assures its
+ durability.
+
+ For more information, see
+ .
+
+
+
+
+
+ Concurrency
+
+ The concept that multiple independent operations happen within the
+ database at the same time.
+ In
PostgreSQL, concurrency is controlled by
+ the multiversion concurrency control
+ mechanism.
+
+
+
+
+
+ Connection
+
+ An established line of communication between a client process and a
+ backend process,
+ usually over a network, supporting a
+ session. This term is
+ sometimes used as a synonym for session.
+
+ For more information, see
+ .
+
+
+
+
+
+ Consistency
+
+ The property that the data in the
+ database
+ is always in compliance with
+ integrity constraints.
+ Transactions may be allowed to violate some of the constraints
+ transiently before it commits, but if such violations are not resolved
+ by the time it commits, such transaction is automatically
+ rolled back.
+ This is one of the
ACID properties.
+
+
+
+
+
+ Constraint
+
+ A restriction on the values of data allowed within a
+ Table.
+
+ For more information, see
+ .
+
+
+
+
+
+ Data Area
+
+
+
+
+ Data Directory
+
+ The base directory on the filesystem of a
+ server that contains all
+ data files and subdirectories associated with a
+ cluster with the
+ exception of tablespaces.
+ The environment variable PGDATA is commonly used to
+ refer to the
+ data directory.
+
+ An instance's storage
+ space comprises the data directory plus any additional tablespaces.
+
+ For more information, see
+ .
+
+
+
+
+
+ Database
+
+ A named collection of
+ SQL objects.
+
+ For more information, see
+ .
+
+
+
+
+
+ Database Server
+
+
+
+
+ Datum
+
+ The internal representation of one value of a
SQL+ data type.
+
+
+
+
+
+ Delete
+
+ A
SQL command which removes
+ rows from a given
+ table
+ or relation.
+
+ For more information, see
+ .
+
+
+
+
+
+ Durability
+
+ The assurance that once a
+ transaction has
+ been committed, the
+ changes remain even after a system failure or crash.
+ This is one of the
ACID properties.
+
+
+
+
+
+ Extension
+
+ A software add-on package that can be installed on an
+ instance to
+ get extra features.
+
+ For more information, see
+ .
+
+
+
+
+
+ File Segment
+
+ A physical file which stores data for a given
+ relation.
+ File segments are limited in size by a configuration value,
+ so if a relation exceeds that size, it is split into multiple segments.
+
+ For more information, see
+ .
+
+ (Don't confuse this term with the similar term
+ WAL segment).
+
+
+
+
+
+ Foreign Data Wrapper
+
+ A means of representing data that is not contained in the local
+ database so that it appears as if were in local
+ table(s). With a Foreign Data Wrapper it is
+ possible to define a foreign server and
+ foreign tables.
+
+ For more information, see
+ .
+
+
+
+
+
+ Foreign Key
+
+ A type of constraint
+ defined on one or more columns
+ in a table which
+ requires the value(s) in those columns to
+ identify zero or one row
+ in another (or, infrequently, the same)
+ table.
+
+
+
+
+
+ Foreign Server
+
+ A named collection of
+ foreign tables which
+ all use the same
+ foreign data wrapper
+ and have other configuration values in common.
+
+ For more information, see
+ .
+
+
+
+
+
+ Foreign Table
+
+ A relation which appears to have
+ rows and
+ columns similar to a
+ regular table, but will forward
+ requests for data through its
+ foreign data wrapper,
+ which will return result sets
+ structured according to the definition of the
+ foreign table.
+
+ For more information, see
+ .
+
+
+
+
+
+ Function
+
+ Any defined transformation of data. Many functions are already defined
+ within
PostgreSQL itself, but user-defined
+ ones can also be added.
+
+ For more information, see
+ .
+
+
+
+
+
+ Global SQL Object
+
+ SQL objects which do
+ not belong to a specific
+ database.
+
+ These objects are
+ roles,
+ tablespaces,
+ replication origins, and subscriptions for logical replication.
+
+
+
+
+
+ Grant
+
+ A
SQL command that is used to allow
+ users or
+ role to access
+ specific objects within the database.
+
+ For more information, see
+ .
+
+
+
+
+
+ Heap
+
+ Contains the values of row
+ attributes (i.e. the data) for a
+ relation.
+ The heap is realized within
+ segment files.
+
+
+
+
+
+ Host
+
+ A computer that communicates with other hosts over a network.
+ This term can be used to refer to either a
+ client
+ or a server.
+
+
+
+
+
+ Index
+
+ A relation that contains
+ data derived from a table
+ (or relation types
+ such as a materialized view).
+ Its internal structure supports fast retrieval of and access to the original
+ data.
+
+ For more information, see
+ .
+
+
+
+
+
+ Insert
+
+ A
SQL command used to add new data into a
+ table.
+
+ For more information, see
+ .
+
+
+
+
+
+ Instance
+
+ An instance is a group of processes,
+ its supporting storage space,
+ plus their
+ common shared memory,
+ running on a single server.
+ The instance
+ handles all key features of a
DBMS: read and write
+ access to files and shared memory, assurance of
+ the
ACID paradigm,
MVCC,
+ connections to client programs, backup,
+ recovery, replication, privileges, etc.
+
+ An instance manages exactly one
+ cluster.
+
+ Many instances can run on the same server as
+ long as their
TCP/IP ports do not conflict.
+ Different instances on a server may use the
+ same or different versions of
PostgreSQL.
+
+
+
+
+
+ Isolation
+
+ The property that the effects of a transaction are not visible to
+ concurrent transactions
+ before it commits.
+ This is one of the
ACID properties.
+
+ For more information, see .
+
+
+
+
+
+ Join
+
+ A
SQL keyword used in
SELECT statements for
+ combining data from multiple relations.
+
+
+
+
+
+ Key
+
+ A means of identifying a row within a
+ table or
+ relation by
+ values contained within one or more
+ attributes
+ in that table.
+
+
+
+
+
+ Lock
+
+ A mechanism that allows a process to limit or prevent simultaneous
+ access to a resource.
+
+
+
+
+
+ Log File
+
+ Log files contain human-readable text lines about events.
+ Examples include login failures, long-running queries, etc.
+
+ For more information, see
+ .
+
+
+
+
+
+ Logger (process)
+
+ If activated, the
+ Logger process
+ writes information about database events into the current
+ log file.
+ When reaching certain time- or
+ volume-dependent criteria, a new log file is created.
+ Also called syslogger.
+
+ For more information, see
+ .
+
+
+
+
+
+ Log Record
+
+ Archaic term for a WAL record.
+
+
+
+
+
+ Logged
+
+ A table is considered
+ logged if changes to it are sent to the
+ WAL. By default, all regular
+ tables are logged. A table can be specified as
+ unlogged either at
+ creation time or via the ALTER TABLE command.
+
+
+
+
+
+ Master (server)
+
+
+
+
+ Materialized
+
+ The property that some information has been pre-computed and stored
+ for later use, rather than computing it on-the-fly.
+
+ This term is used in
+ materialized view,
+ to mean that the data derived from the view's query is stored on
+ disk separately from the sources of that data.
+
+ This term is also used to refer to some multi-step queries to mean that
+ the data resulting from executing a given step is stored in memory
+ (with the possibility of spilling to disk), so that it can be read multiple
+ times by another step.
+
+
+
+
+
+ Materialized View
+
+ A relation that is
+ defined in the same way that a a view
+ is, but stores data in the same way that a
+ table does. It cannot be
+ modified via INSERT, UPDATE, or
+ DELETE operations.
+
+ For more information, see
+ .
+
+
+
+
+
+ Multi-version concurrency control (MVCC)
+
+ A mechanism designed to allow several
+ transactions to be
+ reading and writing the same rows without one process causing other
+ processes to stall.
+ In
PostgreSQL, MVCC is implemented by
+ creating copies (versions) of
+ tuples as they are
+ modified; after transactions that can see the old versions terminate,
+ those old versions need to be removed.
+
+
+
+
+
+ Null
+
+ A concept of non-existence that is a central tenet of Relational
+ Database Theory. It represents the absence of value.
+
+
+
+
+
+ Optimizer
+
+
+
+
+ Parallel Query
+
+ The ability to handle parts of executing a
+ query to take advantage
+ of parallel processes on servers with multiple
CPUs.
+
+
+
+
+
+ Partition
+
+ One of several disjoint (not overlapping) subsets of a larger set.
+
+ In reference to a
+ partitioned table:
+ One of the tables that each contain part of the data of the partitioned table,
+ which is said to be the parent.
+ The partition is itself a table, so it can also be queried directly;
+ at the same time, a partition can sometimes be a partitioned table,
+ allowing hierarchies to be created.
+
+
+
+ In reference to a window function:
+ a partition is a user-defined criteria that identifies which neighboring
+ rows can be considered by the
+ function.
+
+
+
+
+
+ Partitioned Table
+
+ A relation that is
+ in semantic terms the same as a table,
+ but whose storage is distributed across several
+ partitions.
+
+
+
+
+
+ Postmaster (process)
+
+ The very first process of an instance.
+ It starts and manages the other auxiliary processes and creates
+ backend processes
+ on demand.
+
+ For more information, see
+ .
+
+
+
+
+
+ Primary (server)
+
+ When two or more databases
+ are linked via replication,
+ the server
+ that is considered the authoritative source of information is called
+ the primary,
+ also known as a master.
+
+
+
+
+
+ Primary Key
+
+ A special case of a
+ unique constraint
+ defined on a
+ table or other
+ relation that also
+ guarantees that all of the
+ attributes
+ within the primary key
+ do not have null values.
+ As the name implies, there can be only one
+ primary key per table, though it is possible to have multiple unique
+ constraints that also have no null-capable attributes.
+
+
+
+
+
+ Procedure
+
+ A defined set of instructions for manipulating data within a
+ database.
+ A procedure can
+ be written in a variety of programming languages. They are
+ similar to functions,
+ but are different in that they must be invoked via the CALL
+ command rather than the SELECT or PERFORM
+ commands, and they are allowed to make transactional statements such
+ as COMMIT and ROLLBACK.
+
+ For more information, see
+ .
+
+
+
+
+
+ Query
+
+ A request sent by a client to a backend,
+ usually to return results or to modify data on the database.
+
+
+
+
+
+ Query Planner
+
+ The part of
PostgreSQL that is devoted to
+ determining (planning) the most efficient way to
+ execute queries.
+ Also known as query optimizer,
+ optimizer, or simply planner.
+
+
+
+
+
+ Record
+
+
+
+
+ Recycling
+
+
+
+
+ Referential Integrity
+
+ A means of restricting data in one relation
+ by a foreign key
+ so that it must have matching data in another
+ relation.
+
+
+
+
+
+ Relation
+
+ The generic term for all objects in a
+ database
+ that have a name and a list of
+ attributes
+ defined in a specific order.
+ Tables,
+ views,
+ foreign tables,
+ materialized views, and
+ indexes are all relations.
+
+ Class is an archaic synonym for
+ relation.
+
+
+
+
+
+ Replica
+
+ A database that is paired
+ with a primary
+ database and is maintaining a copy of some or all of the primary database's
+ data. The foremost reasons for doing this are to allow for greater access
+ to that data, and to maintain availability of the data in the event that
+ the primary
+ becomes unavailable.
+
+
+
+
+
+ Replication
+
+ The act of reproducing data on one
+ server onto another
+ server called a replica.
+ This can take the form of physical replication,
+ where all file changes from one server are copied verbatim,
+ or logical replication where a defined subset
+ of data changes are conveyed using a higher-level representation.
+
+
+
+
+
+ Result Set
+
+ A data structure transmitted from a
+ backend process to
+ client program upon the completion of a
SQL+ command, usually a SELECT but it can be an
+ INSERT, UPDATE, or
+ DELETE command if the RETURNING
+ clause is specified. The data structure consists of zero or more
+ rows with the same ordered set of
+ attributes.
+
+
+
+
+
+ Revoke
+
+ A command to prevent access to a named set of
+ database objects for a
+ named list of roles.
+
+ For more information, see
+ .
+
+
+
+
+
+ Role
+
+ A collection of access privileges to the
+ instance.
+ Roless are themselves a privilege that can be granted to other roles.
+ This is often done for convenience or to ensure completeness
+ when multiple users need
+ the same privileges.
+
+ For more information, see
+ .
+
+
+
+
+
+ Rollback
+
+ A command to undo all of the operations performed since the beginning
+ of a transaction.
+
+ For more information, see
+ .
+
+
+
+
+
+ Row
+
+
+
+
+ Savepoint
+
+ A special mark inside the sequence of steps in a
+ transaction.
+ Data modifications after this point in time may be reverted
+ to the time of the savepoint.
+
+ For more information, see
+ .
+
+
+
+
+
+ Schema
+
+ A schema is a namespace for SQL objects,
+ which all reside in the same
+ database. Each
+ SQL object must reside in exactly one schema.
+
+ The names of SQL objects of the same type in the same schema are enforced unique.
+ There is no restriction on reusing a name in multiple schemas.
+
+ All system-defined SQL objects reside in schema pg_catalog,
+ and commonly many user-defined SQL objects reside in the default schema
+ public,
+ but it is common and recommended that other schemas are created to hold
+ application-specific SQL objects.
+
+
+
+ More generically, the term Schema is used to mean
+ all data descriptions (table definitions,
+ constraints, comments, etc)
+ for a given database or
+ subset thereof.
+
+ For more information, see
+ .
+
+
+
+
+
+ Segment
+
+
+
+
+ Select
+
+ The
SQL command used to request data from a
+ database.
+ Normally, SELECT commands are not expected to modify the
+ database in any way,
+ but it is possible that
+ functions invoked within
+ the query could have side effects that do modify data.
+
+ For more information, see
+ .
+
+
+
+
+
+
+
+ Server
+
+ A computer on which
PostgreSQL+ instances run.
+ The term server denotes real hardware, a
+ container, or a Virtual Machine.
+
+
+
+
+
+ Session
+
+ A state that allows a client and a backend to interact,
+ communicating over a connection.
+
+
+
+
+
+
+
+ Shared Memory
+
+
RAM which is used by the processes common to an
+ instance.
+ It mirrors parts of database
+ files, provides a transient area for
+ WAL records,
+ and stores additional common information.
+ Note that shared memory belongs to the complete instance, not to a single
+ database.
+
+ The largest part of shared memory is known as shared buffers
+ and is used to mirror part of data files, organized into pages.
+ When a page is modified, it is called a dirty page until it is
+ written back to the file system.
+
+ For more information, see
+ .
+
+
+
+
+
+ SQL Object
+
+ A table,
+ view,
+ materialized view,
+ index,
+ constraint,
+ sequence,
+ function,
+ procedure,
+ trigger,
+ data type, or operator. Every one of those SQL objects
+ belong to exactly one Schema.
+
+ There also exist SQL objects that do not belong to schemas; those include
+ extensions,
+ data type cases,
+ and
+ foreign data wrappers.
+
+ For more information, see
+ .
+
+
+
+
+
+ SQL Standard
+
+ A series of documents that define the
SQL language.
+
+
+
+
+
+ Stats Collector
+
+ This process collects statistical information about the
+ Cluster's activities.
+
+ For more information, see
+ .
+
+
+
+
+
+ System Catalog
+
+ A collection of tables
+ which describe the structure of all
+ SQL objects
+ of each database
+ and the global SQL objects
+ of the cluster.
+ The system catalog resides in the schema pg_catalog.
+ These tables contain data in internal representation and are
+ not typically considered useful for user examination;
+ a number of user-friendlier views
+ also in schema pg_catalog offer more convenient access to
+ some of that information, while additional tables and views
+ exist in schema information_schema that expose some
+ of the same and additional information as mandated by the
+ SQL standard.
+
+ For more information, see
+ .
+
+
+
+
+
+ Table
+
+ A collection of tuples having
+ a common data structure (the same number of
+ attributes, in the same
+ order, having the same name and type per position).
+ A table is the most common form of
+ Relation in
+
+ For more information, see
+ .
+
+
+
+
+
+ Tablespace
+
+ A named location on the server filesystem.
+ All SQL objects
+ which require storage beyond their definition in the
+ system catalog
+ must belong to a single tablespace.
+ Initially, an instance contains a single usable tablespace which is
+ used as the default one for all SQL objects, called pg_default.
+
+ For more information, see
+ .
+
+
+
+
+
+ Temporary Table
+
+ Tables that exist either
+ for the lifetime of a
+ session or a
+ transaction, as
+ specified at the time of creation.
+ The data in them is not visible to other sessions, and is not
+ logged.
+ Temporary tables are often used to store intermediate data for a
+ multi-step operation.
+
+ For more information, see
+ .
+
+
+
+
+
+ Transaction
+
+ A combination of commands that must act as a single
+ atomic command: they all
+ succeed or all fail as a single unit, and their effects are not visible to
+ other sessions until
+ the transaction is complete, and possibly even later, depending on the
+ isolation level.
+
+ For more information, see
+ .
+
+
+
+
+
+ Trigger
+
+ A function which can
+ be defined to execute whenever a certain operation (INSERT,
+ UPDATE, DELETE,
+ TRUNCATE) is applied to a
+ relation.
+ A Trigger executes within the same
+ transaction as the
+ statement which invoked it, and if the function fails, then the invoking
+ statement also fails.
+
+ For more information, see
+ .
+
+
+
+
+
+ Tuple
+
+ A collection of attributes
+ in a fixed order.
+ That order may be defined by the table
+ where the tuple is contained, in which case the tuple is often called a
+ row. It may also be defined by the structure of a
+ result set, in which case it is sometimes called a record.
+
+
+
+
+
+ Unique Constraint
+
+ A type of constraint
+ defined on a relation
+ which restricts the values allowed in one or a combination of columns
+ so that each value or combination of values can only appear once in the
+ relation — that is, no other row in the relation contains values
+ that are equal to those.
+
+ Because null values are
+ not considered equal to each other, multiple rows with null values are
+ allowed to exist without violating the unique constraint.
+
+
+
+
+
+ Unlogged
+
+ The property of certain relations
+ that the changes to them are not reflected in the
+ WAL.
+ This disables replication and crash recovery for these relations.
+
+ The primary use of unlogged tables is for storing
+ transient work data that must be shared across processes.
+
+ Temporary tables
+ are always unlogged.
+
+
+
+
+
+ Update
+
+ A
SQL command used to modify
+ rows
+ that may already exist in a specified table.
+ It cannot create or remove rows.
+
+ For more information, see
+ .
+
+
+
+
+
+ User
+
+ A role that has the
+ LOGIN privilege.
+
+
+
+
+
+ User mapping
+
+ The translation of login credentials in the local
+ database to credentials
+ in a remote data system defined by a
+ foreign data wrapper.
+
+ For more information, see
+ .
+
+
+
+
+
+ Vacuum
+
+ The process of removing outdated tuple
+ versions from tables, and other closely related
+ garbage-collection-like processing required by
PostgreSQL's
+ implementation of MVCC.
+ This can be initiated through the use of
+ the VACUUM command, but can also be handled automatically
+ via autovacuum processes.
+
+ For more information, see
+ .
+
+
+
+
+
+ View
+
+ A relation that is defined by a
+ SELECT statement, but has no storage of its own.
+ Any time a query references a view, the definition of the view is
+ substituted into the query as if the user had typed it as a subquery
+ instead of the name of the view.
+
+ For more information, see
+ .
+
+
+
+
+
+ WAL Archiver (process)
+
+ A process that saves copies of WAL files
+ for the purposes of creating backups or keeping
+ replicas current.
+
+ For more information, see
+ .
+
+
+
+
+
+ WAL File
+
+ Also known as WAL segment or
+ WAL segment file.
+ Each of the sequentially-numbered files that provide storage space for
+ WAL.
+ The files are all of the same predefined size
+ and are written in sequential order, interspersing changes
+ as they occur in multiple simultaneous sessions.
+ If the system crashes, the files are read in order, and each of the
+ changes are replayed to restore the system to the state as it was
+ before the crash.
+
+ Each WAL file can be released after a
+ checkpoint
+ writes all the changes in it to the corresponding data files.
+ Releasing the file can be done either by deleting it, or by changing its
+ name so that it will be used in the future, which is called
+ recycling.
+
+ For more information, see
+ .
+
+
+
+
+
+ WAL
+
+
+
+
+ WAL Record
+
+ A low-level description of an individual data change.
+ It contains sufficient information for the data change to be
+ re-executed (replayed) in case a system failure
+ causes the change to be lost.
+ WAL records use a non-printable binary format.
+
+ For more information, see
+ .
+
+
+
+
+
+ WAL Segment
+
+
+
+
+ WAL Writer (process)
+
+ A process that writes WAL records
+ from shared memory to
+ WAL files.
+
+ For more information, see
+ .
+
+
+
+
+
+ Window Function
+
+ A type of function whose
+ result is based on values found in
+ rows of the same
+ partition.
+ All aggregate functions
+ can be used as window functions, but window functions can also be
+ used to, for example, give ranks to each of the rows in the partition.
+ Also known as analytic functions.
+
+ For more information, see
+ .
+
+
+
+
+
+ Write-Ahead Log
+
+ The journal that keeps track of the changes in the
+ instance as user- and
+ system-invoked operations take place.
+ It comprises many individual
+ WAL records written
+ sequentially to WAL files.
+
+
+
+
+
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