+
+ ACID
+
+ Atomicity,
+ Consistency,
+ Isolation, and
+ Durability.
+ This set of properties of database transactions is intended to
+ guarantee validity in concurrent operation and even in event of
+ errors, power failures, etc.
+
+
+
+
- Aggregate Function
+ Aggregate function
A function that
to make decisions about how to execute
queries.
+ (Don't confuse this term with the ANALYZE option
+ to the command.)
+
- Analytic Function
+ Analytic function
Process of an instance
- which act on behalf of client sessions
- and handle their requests.
+ which acts on behalf of a client session
+ and handles its requests.
(Don't confuse this term with the similar terms
- Background Worker (process)
+ Background worker (process)
Process within an instance,
- Background Writer (process)
+ Background writer (process)
- A process that continuously writes dirty pages from
+ A process that writes dirty
+ data 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
+
+ Bloat
+
+ Space in data pages which does not contain current row versions,
+ such as unused (free) space or outdated row versions.
+
+
+
+
Cast
- Check Constraint
+ Check constraint
A type of constraint
-
- Checkpointer (process)
-
- A specialized process responsible for executing checkpoints.
-
-
-
-
Checkpoint
+
+ Checkpointer (process)
+
+ A specialized process responsible for executing checkpoints.
+
+
+
+
Class (archaic)
-
- 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
A restriction on the values of data allowed within a
- Table.
+ table,
+ or in attributes of a
+
+ domain.
For more information, see
- Data Area
+ Data area
- Data Directory
+ Data directory
The base directory on the filesystem of a
server that contains all
- data files and subdirectories associated with a
- cluster">cluster with the
- exception of tablespaces.
+ data files and subdirectories associated with an
+ instance">instance (with the
+ exception of tablespaces).
The environment variable PGDATA is commonly used to
refer to the
data directory.
- Database Server
+ Database server
+
+ Data page
+
+ The basic structure used to store relation data.
+ All pages are of the same size.
+ Data pages are typically stored on disk, each in a specific file,
+ and can be read to shared buffers
+ where they can be modified, becoming
+ dirty. They become clean when written
+ to disk. New pages, which initially exist in memory only, are also
+ dirty until written.
+
+
+
+
Datum
- The internal representation of one value of a
SQL+ The internal representation of one value of a
n SQL data type.
Delete
- A
SQL command which removes
+ A
n SQL command which removes
rows from a given
table
or relation.
+
+ Epoch
+
+
+
Extension
- File Segment
+ File segment
A physical file which stores data for a given
relation.
- File segments are limited in size by a configuration value,
+ File segments are limited in size by a configuration value
+ (typically 1 gigabyte),
so if a relation exceeds that size, it is split into multiple segments.
- Foreign Data Wrapper
+ 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
+ table(s). With a foreign data wrapper it is
possible to define a foreign server and
- foreign tables.
+ foreign tables.
For more information, see
- Foreign Key
+ Foreign key
A type of constraint
- Foreign Server
+ Foreign server
A named collection of
- Foreign Table
+ Foreign table
A relation which appears to have
- unction">
- Function
+ ork">
+ Fork
- Any defined transformation of data. Many functions are already defined
- within
PostgreSQL itself, but user-defined
- ones can also be added.
+ Each of the separate segmented file sets in which a relation is stored.
+ The main fork is where the actual data resides.
+ There also exist two secondary forks for metadata:
+ the free space map
+ and the visibility map.
+ Unlogged relations
+ also have an init fork.
+
+
+
+
+
+ Free space map (fork)
+
+ A storage structure that keeps metadata about each data page of a table's
+ main fork. The free space map entry for each page stores the
+ amount of free space that's available for future tuples, and is structured
+ to be efficiently searched for available space for a new tuple of a given
+ size.
For more information, see
- ql-createfunction"/>.
+ torage-fsm"/>.
- global-sql-object">
- Global SQL Object
+ function">
+ Function
- SQL objects which do
- not belong to a specific
- database.
+ Any defined transformation of data. Many functions are already defined
+ within
PostgreSQL itself, but user-defined
+ ones can also be added.
- These objects are
- roles,
- tablespaces,
- replication origins, and subscriptions for logical replication.
+ For more information, see
+ .
Grant
- A
SQL command that is used to allow
+ A
n SQL command that is used to allow
users or
role to access
specific objects within the database.
Contains the values of row
attributes (i.e. the data) for a
relation.
- The heap is realized within
- segment files.
+ The heap is realized within one of more
+ file segments
+ in the relation's main fork.
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.
+ A computer that communicates with other computers over a network.
+ This is sometimes used as a synonym for
+ server.
+ It is also used to refer to a computer where
+ client processes run.
Insert
- A
SQL command used to add new data into a
+ A
n SQL command used to add new data into a
table.
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.
+ A set of databases and accompanying global SQL objects that are stored in
+ the same data directory
+ in a single server.
+ If running, one
+ postmaster process
+ manages a group of backend and auxiliary processes that communicate
+ using a common shared memory
+ area. Many instances can run on the same
+ server
+ as long as their
TCP ports do not conflict.
- An instance manages exactly one
- cluster.
+ The instance handles all key features of a
DBMS:
+ read and write access to files and shared memory,
+ assurance of the
ACID properties,
+ connections to client processes,
+ privilege verification, crash recovery, replication, etc.
- 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.
+ In
PostgreSQL, the term
+ cluster is also sometimes used to refer to an instance.
+ (Don't confuse this term with the SQL command CLUSTER.)
Join
- A
SQL keyword used in
SELECT statements for
+ A
n SQL keyword used in
SELECT statements for
combining data from multiple relations.
- Log File
+ Log file
Log files contain human-readable text lines about events.
-
- 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
+ Log record
Archaic term for a WAL record.
+
+ 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
+ .
+
+
+
+
Master (server)
- Materialized View
+ Materialized view
A relation that is
Null
- A concept of non-existence that is a central tenet of Relational
- Database Theory. It represents the absence of value.
+ A concept of non-existence that is a central tenet of relational
+ database theory. It represents the absence of a definite value.
- Parallel Query
+ Parallel query
The ability to handle parts of executing a
- Partitioned Table
+ Partitioned table
A relation that is
- Primary Key
+ Primary key
A special case of a
- Query Planner
+ Query planner
The part of
PostgreSQL that is devoted to
- Referential Integrity
+ Referential integrity
A means of restricting data in one relation
attributes
defined in a specific order.
Tables,
+ sequences,
views,
foreign tables,
- materialized views, and
+ materialized views,
+ composite types, and
indexes are all relations.
- Replica
+ Replica (server)
A database that is paired
- Result Set
+ Result set
A data structure transmitted from a
backend process to
- client program upon the completion of a
SQL+ a client upon the
command, usually a SELECT but it can be an
INSERT, UPDATE, or
DELETE command if the RETURNING
A collection of access privileges to the
instance.
- Roless are themselves a privilege that can be granted to other roles.
+ Roles 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.
Savepoint
- A special mark inside the sequence of steps in a
+ A special mark in the sequence of steps in a
transaction.
Data modifications after this point in time may be reverted
to the time of the savepoint.
Schema
- A schema is a namespace for SQL objects,
+ A schema is a namespace for
+ SQL objects,
which all reside in the same
- database. Each
- SQL object must reside in exactly one schema.
+ 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.
+ The names of SQL objects of the same type in the same schema are enforced
+ to be unique.
There is no restriction on reusing a name in multiple schemas.
- More generically, the term Schema is used to mean
+ More generically, the term schema is used to mean
all data descriptions (table definitions,
constraints, comments, etc)
for a given database or
A computer on which
PostgreSQL instances run.
The term server denotes real hardware, a
- container, or a Virtual Machine.
+ container, or a virtual machine.
+
+ This term is sometimes used to refer to an instance or to a host.
-
- Shared Memory
+ Shared memory
RAM which is used by the processes common to an
+
+ Standby (server)
+
+
+
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.
+ Any object that can be created with a CREATE
+ command. Most objects are specific to one database, and are commonly
+ known as local objects.
+ Roles,
+ tablespaces,
+ replication origins, subscriptions for logical replication, and
+ databases themselves are not local SQL objects since they exist
+ entirely outside of any specific database;
+ they are called global objects.
+
+ Most local objects belong to a specific
+ schema in their containing database.
+ There also exist local objects that do not belong to schemas; some examples are
+ extensions,
+ data type casts, and
+ foreign data wrappers.
For more information, see
- SQL Standard
+ SQL standard
A series of documents that define the
SQL language.
- Stats Collector
+ Stats collector
This process collects statistical information about the
- cluster">Cluster's activities.
+ instance">instance's activities.
For more information, see
- System Catalog
+ 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.
+ of the instance.
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
+ exist in schema information_schema
+ (see ) that expose some
of the same and additional information as mandated by the
SQL standard.
attributes, in the same
order, having the same name and type per position).
A table is the most common form of
- Relation in
+ relation in
- Temporary Table
+ Temporary table
Tables that exist either
+
+ TOAST
+
+ A mechanism by which large attributes of table rows are split and
+ stored in a secondary table, called the TOAST table.
+ Each relation with large attributes has its own TOAST table.
+
+ For more information, see
+ .
+
+
+
+
Transaction
+
+ Transaction ID
+
+ The numerical, unique, sequentially-assigned identifier that each
+ transaction receives when it first causes a database modification.
+ Frequently abbreviated as xid.
+ When stored on disk, xids are only 32-bits wide, so only
+ approximately four billion write transaction IDs can be generated;
+ to permit the system to run for longer than that,
+ epochs are used, also 32 bits wide.
+ When the counter reaches the maximum xid value, it starts over at
+ 3 (values under that are reserved) and the
+ epoch value is incremented by one.
+ In some contexts, the epoch and xid values are
+ considered together as a single 64-bit value.
+
+ For more information, see
+ .
+
+
+
+
Trigger
UPDATE, DELETE,
TRUNCATE) is applied to a
relation.
- A Trigger executes within the same
+ A trigger executes within the same
transaction as the
statement which invoked it, and if the function fails, then the invoking
statement also fails.
- Unique Constraint
+ Unique constraint
A type of constraint
Update
- A
SQL command used to modify
+ A
n SQL command used to modify
rows
that may already exist in a specified table.
It cannot create or remove rows.
Vacuum
- The process of removing outdated tuple
- versions from tables, and other closely related
- garbage-collection-like processing required by
PostgreSQL's
+ The process of removing outdated
+ tuple versions
+ from tables or materialized views, and other closely related
+ 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
+
+ Visibility map (fork)
+
+ A storage structure that keeps metadata about each data page
+ of a table's main fork. The visibility map entry for
+ each page stores two bits: the first one
+ (all-visible) indicates that all tuples
+ in the page are visible to all transactions. The second one
+ (all-frozen) indicate that all tuples
+ in the page are marked frozen.
+
+
+
+
+
+ WAL
+
+
+
- WAL Archiver (process)
+ WAL archiver (process)
A process that saves copies of WAL files
- WAL File
+ WAL file
Also known as WAL segment or
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
+ changes is replayed to restore the system to the state as it was
before the crash.
-
- WAL
-
-
-
- WAL Record
+ WAL record
A low-level description of an individual data change.
- WAL Segment
+ WAL segment
- WAL Writer (process)
+ WAL writer (process)
A process that writes WAL records
- from id="linkend-shared-memory">shared memory to
- id="linkend-wal-file">WAL files.
+ from linkend="glossary-shared-memory">shared memory to
+ linkend="glossary-wal-file">WAL files.
For more information, see
- Window Function
+ Window function
A type of function whose
- Write-Ahead Log
+ Write-ahead log
The journal that keeps track of the changes in the
projects / postgresql.git / commitdiff