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| author | Alvaro Herrera <alvherre@alvh.no-ip.org> | |
| Fri, 3 Apr 2020 16:23:20 +0000 (13:23 -0300) | ||
| committer | Alvaro Herrera <alvherre@alvh.no-ip.org> | |
| Fri, 3 Apr 2020 16:23:20 +0000 (13:23 -0300) |
More work is still needed, but this is a good start.
Co-authored-by: Corey Huinker <corey.huinker@gmail.com>
Co-authored-by: Jürgen Purtz <juergen@purtz.de>
Co-authored-by: Roger Harkavy <rogerharkavy@gmail.com>
Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/CADkLM=eP6HOeqDjn0FdXuGRusQu4oWH_LFsKjjafmhvWD=aSpQ@mail.gmail.com
Co-authored-by: Corey Huinker <corey.huinker@gmail.com>
Co-authored-by: Jürgen Purtz <juergen@purtz.de>
Co-authored-by: Roger Harkavy <rogerharkavy@gmail.com>
Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/CADkLM=eP6HOeqDjn0FdXuGRusQu4oWH_LFsKjjafmhvWD=aSpQ@mail.gmail.com
| doc/src/sgml/filelist.sgml | patch | blob | blame | history | |
| doc/src/sgml/glossary.sgml | [new file with mode: 0644] | patch | blob |
| doc/src/sgml/postgres.sgml | patch | blob | blame | history |
index 1043d0f7ab9efa9b4d7bad9017fb91f1f9b2f63c..cf21ef857e366d79441bf2587263f4d2fd081400 100644 (file)
<!ENTITY limits SYSTEM "limits.sgml">
<!ENTITY acronyms SYSTEM "acronyms.sgml">
+<!ENTITY glossary SYSTEM "glossary.sgml">
<!ENTITY color SYSTEM "color.sgml">
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+<appendix id="glossary">
+ <title>Glossary</title>
+ <para>
+ This is a list of terms and their meaning in the context of
+ <productname>PostgreSQL</productname> and relational database
+ systems in general.
+ </para>
+
+ <glosslist>
+ <glossentry id="glossary-aggregate">
+ <glossterm>Aggregate Function</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-function">function</glossterm> that
+ combines (<firstterm>aggregates</firstterm>) multiple input values,
+ for example by counting, averaging or adding,
+ yielding a single output value.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="functions-aggregate"/>.
+ </para>
+ <glossseealso otherterm="glossary-window-function" />
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-analyze">
+ <glossterm>Analyze (operation)</glossterm>
+ <glossdef>
+ <para>
+ The process of collecting statistics from data in
+ <glossterm linkend="glossary-table">tables</glossterm>
+ and other <glossterm linkend="glossary-relation">relations</glossterm>
+ to help the <glossterm linkend="glossary-planner">query planner</glossterm>
+ to make decisions about how to execute
+ <glossterm linkend="glossary-query">queries</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Analytic Function</glossterm>
+ <glosssee otherterm="glossary-window-function" />
+ </glossentry>
+
+ <glossentry id="glossary-atomic">
+ <glossterm>Atomic</glossterm>
+ <glossdef>
+ <para>
+ In reference to a <glossterm linkend="glossary-datum">datum</glossterm>:
+ the fact that its value that cannot be broken down into smaller
+ components.
+ </para>
+ </glossdef>
+ <glossdef>
+ <para>
+ In reference to a
+ <glossterm linkend="glossary-transaction">database transaction</glossterm>:
+ see <glossterm linkend="glossary-atomicity">atomicity</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-atomicity">
+ <glossterm>Atomicity</glossterm>
+ <glossdef>
+ <para>
+ The property of a <glossterm linkend="glossary-transaction">transaction</glossterm>
+ 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 <acronym>ACID</acronym> properties.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-attribute">
+ <glossterm>Attribute</glossterm>
+ <glossdef>
+ <para>
+ An element with a certain name and data type found within a
+ <glossterm linkend="glossary-tuple">tuple</glossterm> or
+ <glossterm linkend="glossary-table">table</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-autovacuum">
+ <glossterm>Autovacuum</glossterm>
+ <glossdef>
+ <para>
+ A set of background processes that routinely perform
+ <glossterm linkend="glossary-vacuum">vacuum</glossterm>
+ and <glossterm linkend="glossary-analyze">analyze</glossterm>
+ operations.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="autovacuum"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-backend">
+ <glossterm>Backend (process)</glossterm>
+ <glossdef>
+ <para>
+ Process of an <glossterm linkend="glossary-instance">instance</glossterm>
+ which act on behalf of <glossterm linkend="glossary-session">client sessions</glossterm>
+ and handle their requests.
+ </para>
+ <para>
+ (Don't confuse this term with the similar terms
+ <glossterm linkend="glossary-background-worker">Background Worker</glossterm> or
+ <glossterm linkend="glossary-background-writer">Background Writer</glossterm>).
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-background-worker">
+ <glossterm>Background Worker (process)</glossterm>
+ <glossdef>
+ <para>
+ Process within an <glossterm linkend="glossary-instance">instance</glossterm>,
+ which runs system- or user-supplied code.
+ Serves as infrastructure for several features in
+ <productname>PostgreSQL</productname>, such as
+ <glossterm linkend="glossary-replication">logical replication</glossterm>
+ and <glossterm linkend="glossary-parallel-query">parallel queries</glossterm>.
+ In addition, <glossterm linkend="glossary-extension">Extensions</glossterm> can add
+ custom background worker processes.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="bgworker"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-background-writer">
+ <glossterm>Background Writer (process)</glossterm>
+ <glossdef>
+ <para>
+ A process that continuously writes dirty pages from
+ <glossterm linkend="glossary-shared-memory">shared memory</glossterm> to
+ the file system. It wakes up periodically, but works only for a short
+ period in order to distribute its expensive <acronym>I/O</acronym>
+ activity over time to avoid generating larger
+ <acronym>I/O</acronym> peaks which could block other processes.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="runtime-config-resource-background-writer"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-cast">
+ <glossterm>Cast</glossterm>
+ <glossdef>
+ <para>
+ A conversion of a <glossterm linkend="glossary-datum">datum</glossterm>
+ from its current data type to another data type.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createcast"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-catalog">
+ <glossterm>Catalog</glossterm>
+ <glossdef>
+ <para>
+ The <acronym>SQL</acronym> standard uses this term to
+ indicate what is called a
+ <glossterm linkend="glossary-database">database</glossterm> in
+ <productname>PostgreSQL</productname>'s terminology.
+ </para>
+ <para>
+ (Don't confuse this term with
+ <glossterm linkend="glossary-system-catalog">system catalog</glossterm>).
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="manage-ag-overview"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-check-constraint">
+ <glossterm>Check Constraint</glossterm>
+ <glossdef>
+ <para>
+ A type of <glossterm linkend="glossary-constraint">constraint</glossterm>
+ defined on a <glossterm linkend="glossary-relation">relation</glossterm>
+ which restricts the values allowed in one or more
+ <glossterm linkend="glossary-attribute">attributes</glossterm>. 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.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="ddl-constraints"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-checkpointer">
+ <glossterm>Checkpointer (process)</glossterm>
+ <glossdef>
+ <para>
+ A specialized process responsible for executing checkpoints.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-checkpoint">
+ <glossterm>Checkpoint</glossterm>
+ <glossdef>
+ <para>
+ A point in the <glossterm linkend="glossary-wal">WAL</glossterm> sequence
+ at which it is guaranteed that the heap and index data files have been
+ updated with all information from
+ <glossterm linkend="glossary-shared-memory">shared memory</glossterm>
+ modified before that checkpoint;
+ a <firstterm>checkpoint record</firstterm> is written and flushed to WAL
+ to mark that point.
+ </para>
+ <para>
+ 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 <command>CHECKPOINT</command>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="wal-configuration"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Class (archaic)</glossterm>
+ <glosssee otherterm="glossary-relation" />
+ </glossentry>
+
+ <glossentry id="glossary-client">
+ <glossterm>Client (process)</glossterm>
+ <glossdef>
+ <para>
+ Any process, possibly remote, that establishes a
+ <glossterm linkend="glossary-session">session</glossterm>
+ by <glossterm linkend="glossary-connection">connecting</glossterm> to an
+ <glossterm linkend="glossary-instance">instance</glossterm>
+ to interact with a <glossterm linkend="glossary-database">database</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-cluster">
+ <glossterm>Cluster</glossterm>
+ <glossdef>
+ <para>
+ A group of <glossterm linkend="glossary-database">databases</glossterm> plus their
+ <glossterm linkend="glossary-global-sql-object">global SQL objects</glossterm>. The
+ <firstterm>cluster</firstterm> is managed by exactly one
+ <glossterm linkend="glossary-instance">instance</glossterm>. A newly created
+ Cluster will have three databases created automatically. They are
+ <literal>template0</literal>, <literal>template1</literal>, and
+ <literal>postgres</literal>. It is expected that an application will
+ create one or more additional database aside from these three.
+ </para>
+ <para>
+ (Don't confuse the <productname>PostgreSQL</productname>-specific term
+ <glossterm linkend="glossary-cluster">Cluster</glossterm> with the SQL
+ command <command>CLUSTER</command>).
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-column">
+ <glossterm>Column</glossterm>
+ <glossdef>
+ <para>
+ An <glossterm linkend="glossary-attribute">attribute</glossterm> found in
+ a <glossterm linkend="glossary-table">table</glossterm> or
+ <glossterm linkend="glossary-view">view</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-commit">
+ <glossterm>Commit</glossterm>
+ <glossdef>
+ <para>
+ The act of finalizing a
+ <glossterm linkend="glossary-transaction">transaction</glossterm> within
+ the <glossterm linkend="glossary-database">database</glossterm>, which
+ makes it visible to other transactions and assures its
+ <glossterm linkend="glossary-durability">durability</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-commit"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-concurrency">
+ <glossterm>Concurrency</glossterm>
+ <glossdef>
+ <para>
+ The concept that multiple independent operations happen within the
+ <glossterm linkend="glossary-database">database</glossterm> at the same time.
+ In <productname>PostgreSQL</productname>, concurrency is controlled by
+ the <glossterm linkend="glossary-mvcc">multiversion concurrency control</glossterm>
+ mechanism.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-connection">
+ <glossterm>Connection</glossterm>
+ <glossdef>
+ <para>
+ An established line of communication between a client process and a
+ <glossterm linkend="glossary-backend">backend</glossterm> process,
+ usually over a network, supporting a
+ <glossterm linkend="glossary-session">session</glossterm>. This term is
+ sometimes used as a synonym for session.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="runtime-config-connection"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-consistency">
+ <glossterm>Consistency</glossterm>
+ <glossdef>
+ <para>
+ The property that the data in the
+ <glossterm linkend="glossary-database">database</glossterm>
+ is always in compliance with
+ <glossterm linkend="glossary-constraint">integrity constraints</glossterm>.
+ 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
+ <glossterm linkend="glossary-rollback">rolled back</glossterm>.
+ This is one of the <acronym>ACID</acronym> properties.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-constraint">
+ <glossterm>Constraint</glossterm>
+ <glossdef>
+ <para>
+ A restriction on the values of data allowed within a
+ <glossterm linkend="glossary-table">Table</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="ddl-constraints"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Data Area</glossterm>
+ <glosssee otherterm="glossary-data-directory" />
+ </glossentry>
+
+ <glossentry id="glossary-data-directory">
+ <glossterm>Data Directory</glossterm>
+ <glossdef>
+ <para>
+ The base directory on the filesystem of a
+ <glossterm linkend="glossary-server">server</glossterm> that contains all
+ data files and subdirectories associated with a
+ <glossterm linkend="glossary-cluster">cluster</glossterm> with the
+ exception of <glossterm linkend="glossary-tablespace">tablespaces</glossterm>.
+ The environment variable <literal>PGDATA</literal> is commonly used to
+ refer to the
+ <glossterm linkend="glossary-data-directory">data directory</glossterm>.
+ </para>
+ <para>
+ An <glossterm linkend="glossary-instance">instance</glossterm>'s storage
+ space comprises the data directory plus any additional tablespaces.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="storage-file-layout"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-database">
+ <glossterm>Database</glossterm>
+ <glossdef>
+ <para>
+ A named collection of
+ <glossterm linkend="glossary-sql-object">SQL objects</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="manage-ag-overview"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Database Server</glossterm>
+ <glosssee otherterm="glossary-instance" />
+ </glossentry>
+
+ <glossentry id="glossary-datum">
+ <glossterm>Datum</glossterm>
+ <glossdef>
+ <para>
+ The internal representation of one value of a <acronym>SQL</acronym>
+ data type.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-delete">
+ <glossterm>Delete</glossterm>
+ <glossdef>
+ <para>
+ A <acronym>SQL</acronym> command which removes
+ <glossterm linkend="glossary-tuple">rows</glossterm> from a given
+ <glossterm linkend="glossary-table">table</glossterm>
+ or <glossterm linkend="glossary-relation">relation</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-delete"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-durability">
+ <glossterm>Durability</glossterm>
+ <glossdef>
+ <para>
+ The assurance that once a
+ <glossterm linkend="glossary-transaction">transaction</glossterm> has
+ been <glossterm linkend="glossary-commit">committed</glossterm>, the
+ changes remain even after a system failure or crash.
+ This is one of the <acronym>ACID</acronym> properties.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-extension">
+ <glossterm>Extension</glossterm>
+ <glossdef>
+ <para>
+ A software add-on package that can be installed on an
+ <glossterm linkend="glossary-instance">instance</glossterm> to
+ get extra features.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="extend-extensions" />.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-file-segment">
+ <glossterm>File Segment</glossterm>
+ <glossdef>
+ <para>
+ A physical file which stores data for a given
+ <glossterm linkend="glossary-relation">relation</glossterm>.
+ File segments are limited in size by a configuration value,
+ so if a relation exceeds that size, it is split into multiple segments.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="storage-file-layout"/>.
+ </para>
+ <para>
+ (Don't confuse this term with the similar term
+ <glossterm linkend="glossary-wal-file">WAL segment</glossterm>).
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-foreign-data-wrapper">
+ <glossterm>Foreign Data Wrapper</glossterm>
+ <glossdef>
+ <para>
+ A means of representing data that is not contained in the local
+ <glossterm linkend="glossary-database">database</glossterm> so that it appears as if were in local
+ <glossterm linkend="glossary-table">table(s)</glossterm>. With a Foreign Data Wrapper it is
+ possible to define a <glossterm linkend="glossary-foreign-server">foreign server</glossterm> and
+ <glossterm linkend="glossary-foreign-table">foreign table</glossterm>s.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createforeigndatawrapper"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-foreign-key">
+ <glossterm>Foreign Key</glossterm>
+ <glossdef>
+ <para>
+ A type of <glossterm linkend="glossary-constraint">constraint</glossterm>
+ defined on one or more <glossterm linkend="glossary-column">columns</glossterm>
+ in a <glossterm linkend="glossary-table">table</glossterm> which
+ requires the value(s) in those <glossterm linkend="glossary-column">columns</glossterm> to
+ identify zero or one <glossterm linkend="glossary-tuple">row</glossterm>
+ in another (or, infrequently, the same)
+ <glossterm linkend="glossary-table">table</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-foreign-server">
+ <glossterm>Foreign Server</glossterm>
+ <glossdef>
+ <para>
+ A named collection of
+ <glossterm linkend="glossary-foreign-table">foreign tables</glossterm> which
+ all use the same
+ <glossterm linkend="glossary-foreign-data-wrapper">foreign data wrapper</glossterm>
+ and have other configuration values in common.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createserver"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-foreign-table">
+ <glossterm>Foreign Table</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-relation">relation</glossterm> which appears to have
+ <glossterm linkend="glossary-tuple">rows</glossterm> and
+ <glossterm linkend="glossary-column">columns</glossterm> similar to a
+ regular <glossterm linkend="glossary-table">table</glossterm>, but will forward
+ requests for data through its
+ <glossterm linkend="glossary-foreign-data-wrapper">foreign data wrapper</glossterm>,
+ which will return <glossterm linkend="glossary-result-set">result sets</glossterm>
+ structured according to the definition of the
+ <glossterm linkend="glossary-foreign-table">foreign table</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createforeigntable"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-function">
+ <glossterm>Function</glossterm>
+ <glossdef>
+ <para>
+ Any defined transformation of data. Many functions are already defined
+ within <productname>PostgreSQL</productname> itself, but user-defined
+ ones can also be added.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createfunction"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-global-sql-object">
+ <glossterm>Global SQL Object</glossterm>
+ <glossdef>
+ <para>
+ <glossterm linkend="glossary-sql-object">SQL objects</glossterm> which do
+ not belong to a specific
+ <glossterm linkend="glossary-database">database</glossterm>.
+ </para>
+ <para>
+ These objects are
+ <glossterm linkend="glossary-role">roles</glossterm>,
+ <glossterm linkend="glossary-tablespace">tablespaces</glossterm>,
+ replication origins, and subscriptions for logical replication.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-grant">
+ <glossterm>Grant</glossterm>
+ <glossdef>
+ <para>
+ A <acronym>SQL</acronym> command that is used to allow
+ <glossterm linkend="glossary-user">users</glossterm> or
+ <glossterm linkend="glossary-role">role</glossterm> to access
+ specific objects within the <glossterm linkend="glossary-database">database</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-grant"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-heap">
+ <glossterm>Heap</glossterm>
+ <glossdef>
+ <para>
+ Contains the values of <glossterm linkend="glossary-tuple">row</glossterm>
+ attributes (i.e. the data) for a
+ <glossterm linkend="glossary-relation">relation</glossterm>.
+ The heap is realized within
+ <glossterm linkend="glossary-file-segment">segment files</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-host">
+ <glossterm>Host</glossterm>
+ <glossdef>
+ <para>
+ A computer that communicates with other hosts over a network.
+ This term can be used to refer to either a
+ <glossterm linkend="glossary-client">client</glossterm>
+ or a <glossterm linkend="glossary-server">server</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-index">
+ <glossterm>Index</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-relation">relation</glossterm> that contains
+ data derived from a <glossterm linkend="glossary-table">table</glossterm>
+ (or <glossterm linkend="glossary-relation">relation</glossterm> types
+ such as a <glossterm linkend="glossary-materialized-view">materialized view</glossterm>).
+ Its internal structure supports fast retrieval of and access to the original
+ data.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createindex"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-insert">
+ <glossterm>Insert</glossterm>
+ <glossdef>
+ <para>
+ A <acronym>SQL</acronym> command used to add new data into a
+ <glossterm linkend="glossary-table">table</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-insert"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-instance">
+ <glossterm>Instance</glossterm>
+ <glossdef>
+ <para>
+ An <glossterm>instance</glossterm> is a group of processes,
+ its supporting <glossterm linkend="glossary-data-directory">storage space</glossterm>,
+ plus their
+ common <glossterm linkend="glossary-shared-memory">shared memory</glossterm>,
+ running on a single <glossterm linkend="glossary-server">server</glossterm>.
+ The <glossterm linkend="glossary-instance">instance</glossterm>
+ handles all key features of a <acronym>DBMS</acronym>: read and write
+ access to files and shared memory, assurance of
+ the <acronym>ACID</acronym> paradigm, <acronym>MVCC</acronym>,
+ <glossterm linkend="glossary-connection">connections</glossterm> to client programs, backup,
+ recovery, replication, privileges, etc.
+ </para>
+ <para>
+ An <glossterm>instance</glossterm> manages exactly one
+ <glossterm linkend="glossary-cluster">cluster</glossterm>.
+ </para>
+ <para>
+ Many <glossterm>instances</glossterm> can run on the same server as
+ long as their <acronym>TCP/IP</acronym> ports do not conflict.
+ Different instances on a server may use the
+ same or different versions of <productname>PostgreSQL</productname>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-isolation">
+ <glossterm>Isolation</glossterm>
+ <glossdef>
+ <para>
+ The property that the effects of a transaction are not visible to
+ <glossterm linkend="glossary-concurrency">concurrent transactions</glossterm>
+ before it commits.
+ This is one of the <acronym>ACID</acronym> properties.
+ </para>
+ <para>
+ For more information, see <xref linkend="transaction-iso" />.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-join">
+ <glossterm>Join</glossterm>
+ <glossdef>
+ <para>
+ A <acronym>SQL</acronym> keyword used in <command>SELECT</command> statements for
+ combining data from multiple <glossterm linkend="glossary-relation">relations</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-key">
+ <glossterm>Key</glossterm>
+ <glossdef>
+ <para>
+ A means of identifying a <glossterm linkend="glossary-tuple">row</glossterm> within a
+ <glossterm linkend="glossary-table">table</glossterm> or
+ <glossterm linkend="glossary-relation">relation</glossterm> by
+ values contained within one or more
+ <glossterm linkend="glossary-attribute">attributes</glossterm>
+ in that table.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-lock">
+ <glossterm>Lock</glossterm>
+ <glossdef>
+ <para>
+ A mechanism that allows a process to limit or prevent simultaneous
+ access to a resource.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-log-file">
+ <glossterm>Log File</glossterm>
+ <glossdef>
+ <para>
+ Log files contain human-readable text lines about events.
+ Examples include login failures, long-running queries, etc.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="logfile-maintenance"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-logger">
+ <glossterm>Logger (process)</glossterm>
+ <glossdef>
+ <para>
+ If activated, the
+ <glossterm linkend="glossary-logger">Logger</glossterm> process
+ writes information about database events into the current
+ <glossterm linkend="glossary-log-file">log file</glossterm>.
+ When reaching certain time- or
+ volume-dependent criteria, a new log file is created.
+ Also called <firstterm>syslogger</firstterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="runtime-config-logging"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-log-record">
+ <glossterm>Log Record</glossterm>
+ <glossdef>
+ <para>
+ Archaic term for a <glossterm linkend="glossary-wal-record">WAL record</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-logged">
+ <glossterm>Logged</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-table">table</glossterm> is considered
+ <glossterm linkend="glossary-logged">logged</glossterm> if changes to it are sent to the
+ <glossterm linkend="glossary-wal">WAL</glossterm>. By default, all regular
+ tables are logged. A table can be specified as
+ <glossterm linkend="glossary-unlogged">unlogged</glossterm> either at
+ creation time or via the <command>ALTER TABLE</command> command.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Master (server)</glossterm>
+ <glosssee otherterm="glossary-primary-server" />
+ </glossentry>
+
+ <glossentry id="glossary-materialized">
+ <glossterm>Materialized</glossterm>
+ <glossdef>
+ <para>
+ The property that some information has been pre-computed and stored
+ for later use, rather than computing it on-the-fly.
+ </para>
+ <para>
+ This term is used in
+ <glossterm linkend="glossary-materialized-view">materialized view</glossterm>,
+ to mean that the data derived from the view's query is stored on
+ disk separately from the sources of that data.
+ </para>
+ <para>
+ 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.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-materialized-view">
+ <glossterm>Materialized View</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-relation">relation</glossterm> that is
+ defined in the same way that a a <glossterm linkend="glossary-view">view</glossterm>
+ is, but stores data in the same way that a
+ <glossterm linkend="glossary-table">table</glossterm> does. It cannot be
+ modified via <command>INSERT</command>, <command>UPDATE</command>, or
+ <command>DELETE</command> operations.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-creatematerializedview"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-mvcc">
+ <glossterm>Multi-version concurrency control (MVCC)</glossterm>
+ <glossdef>
+ <para>
+ A mechanism designed to allow several
+ <glossterm linkend="glossary-transaction">transactions</glossterm> to be
+ reading and writing the same rows without one process causing other
+ processes to stall.
+ In <productname>PostgreSQL</productname>, MVCC is implemented by
+ creating copies (<firstterm>versions</firstterm>) of
+ <glossterm linkend="glossary-tuple">tuples</glossterm> as they are
+ modified; after transactions that can see the old versions terminate,
+ those old versions need to be removed.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-null">
+ <glossterm>Null</glossterm>
+ <glossdef>
+ <para>
+ A concept of non-existence that is a central tenet of Relational
+ Database Theory. It represents the absence of value.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Optimizer</glossterm>
+ <glosssee otherterm="glossary-planner" />
+ </glossentry>
+
+ <glossentry id="glossary-parallel-query">
+ <glossterm>Parallel Query</glossterm>
+ <glossdef>
+ <para>
+ The ability to handle parts of executing a
+ <glossterm linkend="glossary-query">query</glossterm> to take advantage
+ of parallel processes on servers with multiple <acronym>CPU</acronym>s.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-partition">
+ <glossterm>Partition</glossterm>
+ <glossdef>
+ <para>
+ One of several disjoint (not overlapping) subsets of a larger set.
+ </para>
+ <para>
+ In reference to a
+ <glossterm linkend="glossary-partitioned-table">partitioned table</glossterm>:
+ One of the tables that each contain part of the data of the partitioned table,
+ which is said to be the <firstterm>parent</firstterm>.
+ 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.
+ </para>
+ </glossdef>
+ <glossdef>
+ <para>
+ In reference to a <glossterm linkend="glossary-window-function">window function</glossterm>:
+ a partition is a user-defined criteria that identifies which neighboring
+ <glossterm linkend="glossary-tuple">rows</glossterm> can be considered by the
+ function.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-partitioned-table">
+ <glossterm>Partitioned Table</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-relation">relation</glossterm> that is
+ in semantic terms the same as a <glossterm linkend="glossary-table">table</glossterm>,
+ but whose storage is distributed across several
+ <glossterm linkend="glossary-partition">partitions</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-postmaster">
+ <glossterm>Postmaster (process)</glossterm>
+ <glossdef>
+ <para>
+ The very first process of an <glossterm linkend="glossary-instance">instance</glossterm>.
+ It starts and manages the other auxiliary processes and creates
+ <glossterm linkend="glossary-backend">backend processes</glossterm>
+ on demand.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="server-start"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-primary-server">
+ <glossterm>Primary (server)</glossterm>
+ <glossdef>
+ <para>
+ When two or more <glossterm linkend="glossary-database">databases</glossterm>
+ are linked via <glossterm linkend="glossary-replication">replication</glossterm>,
+ the <glossterm linkend="glossary-server">server</glossterm>
+ that is considered the authoritative source of information is called
+ the <firstterm>primary</firstterm>,
+ also known as a <firstterm>master</firstterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-primary-key">
+ <glossterm>Primary Key</glossterm>
+ <glossdef>
+ <para>
+ A special case of a
+ <glossterm linkend="glossary-unique-constraint">unique constraint</glossterm>
+ defined on a
+ <glossterm linkend="glossary-table">table</glossterm> or other
+ <glossterm linkend="glossary-relation">relation</glossterm> that also
+ guarantees that all of the
+ <glossterm linkend="glossary-attribute">attributes</glossterm>
+ within the <glossterm linkend="glossary-primary-key">primary key</glossterm>
+ do not have <glossterm linkend="glossary-null">null</glossterm> 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.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-procedure">
+ <glossterm>Procedure</glossterm>
+ <glossdef>
+ <para>
+ A defined set of instructions for manipulating data within a
+ <glossterm linkend="glossary-database">database</glossterm>.
+ A <glossterm linkend="glossary-procedure">procedure</glossterm> can
+ be written in a variety of programming languages. They are
+ similar to <glossterm linkend="glossary-function">functions</glossterm>,
+ but are different in that they must be invoked via the <command>CALL</command>
+ command rather than the <command>SELECT</command> or <command>PERFORM</command>
+ commands, and they are allowed to make transactional statements such
+ as <command>COMMIT</command> and <command>ROLLBACK</command>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createprocedure"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-query">
+ <glossterm>Query</glossterm>
+ <glossdef>
+ <para>
+ A request sent by a client to a <glossterm linkend="glossary-backend">backend</glossterm>,
+ usually to return results or to modify data on the database.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-planner">
+ <glossterm>Query Planner</glossterm>
+ <glossdef>
+ <para>
+ The part of <productname>PostgreSQL</productname> that is devoted to
+ determining (<firstterm>planning</firstterm>) the most efficient way to
+ execute <glossterm linkend="glossary-query">queries</glossterm>.
+ Also known as <firstterm>query optimizer</firstterm>,
+ <firstterm>optimizer</firstterm>, or simply <firstterm>planner</firstterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Record</glossterm>
+ <glosssee otherterm="glossary-tuple" />
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Recycling</glossterm>
+ <glosssee otherterm="glossary-wal-file" />
+ </glossentry>
+
+ <glossentry id="glossary-referential-integrity">
+ <glossterm>Referential Integrity</glossterm>
+ <glossdef>
+ <para>
+ A means of restricting data in one <glossterm linkend="glossary-relation">relation</glossterm>
+ by a <glossterm linkend="glossary-foreign-key">foreign key</glossterm>
+ so that it must have matching data in another
+ <glossterm linkend="glossary-relation">relation</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-relation">
+ <glossterm>Relation</glossterm>
+ <glossdef>
+ <para>
+ The generic term for all objects in a
+ <glossterm linkend="glossary-database">database</glossterm>
+ that have a name and a list of
+ <glossterm linkend="glossary-attribute">attributes</glossterm>
+ defined in a specific order.
+ <glossterm linkend="glossary-table">Tables</glossterm>,
+ <glossterm linkend="glossary-view">views</glossterm>,
+ <glossterm linkend="glossary-foreign-table">foreign tables</glossterm>,
+ <glossterm linkend="glossary-materialized-view">materialized views</glossterm>, and
+ <glossterm linkend="glossary-index">indexes</glossterm> are all relations.
+ </para>
+ <para>
+ <firstterm>Class</firstterm> is an archaic synonym for
+ <firstterm>relation</firstterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-replica">
+ <glossterm>Replica</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-database">database</glossterm> that is paired
+ with a <glossterm linkend="glossary-primary-server">primary</glossterm>
+ 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 <glossterm linkend="glossary-primary-server">primary</glossterm>
+ becomes unavailable.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-replication">
+ <glossterm>Replication</glossterm>
+ <glossdef>
+ <para>
+ The act of reproducing data on one
+ <glossterm linkend="glossary-server">server</glossterm> onto another
+ server called a <glossterm linkend="glossary-replica">replica</glossterm>.
+ This can take the form of <firstterm>physical replication</firstterm>,
+ where all file changes from one server are copied verbatim,
+ or <firstterm>logical replication</firstterm> where a defined subset
+ of data changes are conveyed using a higher-level representation.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-result-set">
+ <glossterm>Result Set</glossterm>
+ <glossdef>
+ <para>
+ A data structure transmitted from a
+ <glossterm linkend="glossary-backend">backend process</glossterm> to
+ client program upon the completion of a <acronym>SQL</acronym>
+ command, usually a <command>SELECT</command> but it can be an
+ <command>INSERT</command>, <command>UPDATE</command>, or
+ <command>DELETE</command> command if the <literal>RETURNING</literal>
+ clause is specified. The data structure consists of zero or more
+ <glossterm linkend="glossary-tuple">rows</glossterm> with the same ordered set of
+ <glossterm linkend="glossary-attribute">attributes</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-revoke">
+ <glossterm>Revoke</glossterm>
+ <glossdef>
+ <para>
+ A command to prevent access to a named set of
+ <glossterm linkend="glossary-database">database</glossterm> objects for a
+ named list of <glossterm linkend="glossary-role">roles</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-revoke"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-role">
+ <glossterm>Role</glossterm>
+ <glossdef>
+ <para>
+ A collection of access privileges to the
+ <glossterm linkend="glossary-database">instance</glossterm>.
+ Roless are themselves a privilege that can be granted to other roles.
+ This is often done for convenience or to ensure completeness
+ when multiple <glossterm linkend="glossary-user">users</glossterm> need
+ the same privileges.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createrole"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-rollback">
+ <glossterm>Rollback</glossterm>
+ <glossdef>
+ <para>
+ A command to undo all of the operations performed since the beginning
+ of a <glossterm linkend="glossary-transaction">transaction</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-rollback"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Row</glossterm>
+ <glosssee otherterm="glossary-tuple" />
+ </glossentry>
+
+ <glossentry id="glossary-savepoint">
+ <glossterm>Savepoint</glossterm>
+ <glossdef>
+ <para>
+ A special mark inside the sequence of steps in a
+ <glossterm linkend="glossary-transaction">transaction</glossterm>.
+ Data modifications after this point in time may be reverted
+ to the time of the savepoint.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-savepoint"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-schema">
+ <glossterm>Schema</glossterm>
+ <glossdef>
+ <para>
+ A schema is a namespace for <glossterm linkend="glossary-sql-object">SQL objects</glossterm>,
+ which all reside in the same
+ <glossterm linkend="glossary-database">database</glossterm>. Each
+ SQL object must reside in exactly one schema.
+ </para>
+ <para>
+ 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.
+ </para>
+ <para>
+ All system-defined SQL objects reside in schema <literal>pg_catalog</literal>,
+ and commonly many user-defined SQL objects reside in the default schema
+ <literal>public</literal>,
+ but it is common and recommended that other schemas are created to hold
+ application-specific SQL objects.
+ </para>
+ </glossdef>
+ <glossdef>
+ <para>
+ More generically, the term <firstterm>Schema</firstterm> is used to mean
+ all data descriptions (<glossterm linkend="glossary-table">table</glossterm> definitions,
+ <glossterm linkend="glossary-constraint">constraints</glossterm>, comments, etc)
+ for a given <glossterm linkend="glossary-database">database</glossterm> or
+ subset thereof.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="ddl-schemas"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>Segment</glossterm>
+ <glosssee otherterm="glossary-file-segment" />
+ </glossentry>
+
+ <glossentry id="glossary-select">
+ <glossterm>Select</glossterm>
+ <glossdef>
+ <para>
+ The <acronym>SQL</acronym> command used to request data from a
+ <glossterm linkend="glossary-database">database</glossterm>.
+ Normally, <command>SELECT</command> commands are not expected to modify the
+ <glossterm linkend="glossary-database">database</glossterm> in any way,
+ but it is possible that
+ <glossterm linkend="glossary-function">functions</glossterm> invoked within
+ the query could have side effects that do modify data.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-select"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+<!-- XXX should define all other isolation levels (and improve this definition)
+ <glossentry id="glossary-serializable">
+ <glossterm>Serializable (isolation level)</glossterm>
+ <glossdef>
+ <para>
+ Transactions defined as <literal>SERIALIZABLE</literal> are unable to
+ see changes made within other transactions. In effect, for the
+ initializing session the entire <glossterm linkend="glossary-database">database</glossterm>
+ appears to be frozen for the duration of the
+ <glossterm linkend="glossary-transaction">Transaction</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+-->
+
+ <glossentry id="glossary-server">
+ <glossterm>Server</glossterm>
+ <glossdef>
+ <para>
+ A computer on which <productname>PostgreSQL</productname>
+ <glossterm linkend="glossary-instance">instances</glossterm> run.
+ The term <firstterm>server</firstterm> denotes real hardware, a
+ container, or a Virtual Machine.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-session">
+ <glossterm>Session</glossterm>
+ <glossdef>
+ <para>
+ A state that allows a client and a backend to interact,
+ communicating over a <glossterm linkend="glossary-connection">connection</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+<!-- XXX we should have a much more concise definition
+ <glossentry id="glossary-sequence">
+ <glossterm>Sequence</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-database">Database</glossterm> object which
+ represents the mathematical concept of a numerical integral sequence.
+ It can be thought of as a <glossterm linkend="glossary-table">Table</glossterm>
+ with exactly one <glossterm linkend="glossary-tuple">Row</glossterm> and
+ one <glossterm linkend="glossary-column">Column</glossterm>. The
+ value stored is known as the current value. A
+ <glossterm linkend="glossary-sequence">Sequence</glossterm> has a defined
+ direction (usually increasing) and an interval step (usually 1).
+ Whenever the <literal>NEXTVAL</literal> pseudo-column of a
+ <glossterm linkend="glossary-sequence">Sequence</glossterm> is accessed,
+ the current value is moved in the defined direction by the defined
+ interval step, that value is returned to the invoking query,
+ and the current value of the sequence is updated to reflect the new value.
+ The value can be updated multiple times in a single query,
+ the net effect being that each row selected will have a different value.
+ Values taken from a
+ <glossterm linkend="glossary-sequence">Sequence</glossterm> are never
+ reverted, even in the case of a
+ <glossterm linkend="glossary-rollback">Rollback</glossterm>, which means
+ that the <glossterm linkend="glossary-sequence">Sequence</glossterm>
+ will never generate the same number twice, which makes it useful for
+ generating
+ <glossterm linkend="glossary-primary-key">Primary Key</glossterm> values.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createsequence"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+-->
+
+ <glossentry id="glossary-shared-memory">
+ <glossterm>Shared Memory</glossterm>
+ <glossdef>
+ <para>
+ <acronym>RAM</acronym> which is used by the processes common to an
+ <glossterm linkend="glossary-instance">instance</glossterm>.
+ It mirrors parts of <glossterm linkend="glossary-database">database</glossterm>
+ files, provides a transient area for
+ <glossterm linkend="glossary-wal-record">WAL records</glossterm>,
+ and stores additional common information.
+ Note that shared memory belongs to the complete instance, not to a single
+ database.
+ </para>
+ <para>
+ The largest part of shared memory is known as <firstterm>shared buffers</firstterm>
+ 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.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="runtime-config-resource-memory"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-sql-object">
+ <glossterm>SQL Object</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-table">table</glossterm>,
+ <glossterm linkend="glossary-view">view</glossterm>,
+ <glossterm linkend="glossary-materialized-view">materialized view</glossterm>,
+ <glossterm linkend="glossary-index">index</glossterm>,
+ <glossterm linkend="glossary-constraint">constraint</glossterm>,
+<!-- XXX define sequence <glossterm linkend="glossary-sequence"> --> sequence,
+ <glossterm linkend="glossary-function">function</glossterm>,
+ <glossterm linkend="glossary-procedure">procedure</glossterm>,
+ <glossterm linkend="glossary-trigger">trigger</glossterm>,
+ data type, or operator. Every one of those SQL objects
+ belong to exactly one <glossterm linkend="glossary-schema">Schema</glossterm>.
+ </para>
+ <para>
+ There also exist SQL objects that do not belong to schemas; those include
+ <glossterm linkend="glossary-extension">extensions</glossterm>,
+ <glossterm linkend="glossary-cast">data type cases</glossterm>,
+ and
+ <glossterm linkend="glossary-foreign-data-wrapper">foreign data wrappers</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="manage-ag-overview"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-sql-standard">
+ <glossterm>SQL Standard</glossterm>
+ <glossdef>
+ <para>
+ A series of documents that define the <acronym>SQL</acronym> language.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-stats-collector">
+ <glossterm>Stats Collector</glossterm>
+ <glossdef>
+ <para>
+ This process collects statistical information about the
+ <glossterm linkend="glossary-cluster">Cluster</glossterm>'s activities.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="monitoring-stats"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-system-catalog">
+ <glossterm>System Catalog</glossterm>
+ <glossdef>
+ <para>
+ A collection of <glossterm linkend="glossary-table">tables</glossterm>
+ which describe the structure of all
+ <glossterm linkend="glossary-sql-object">SQL objects</glossterm>
+ of each <glossterm linkend="glossary-database">database</glossterm>
+ and the <glossterm linkend="glossary-global-sql-object">global SQL objects</glossterm>
+ of the <glossterm linkend="glossary-cluster">cluster</glossterm>.
+ The system catalog resides in the schema <literal>pg_catalog</literal>.
+ These tables contain data in internal representation and are
+ not typically considered useful for user examination;
+ a number of user-friendlier <glossterm linkend="glossary-view">views</glossterm>
+ also in schema <literal>pg_catalog</literal> offer more convenient access to
+ some of that information, while additional tables and views
+ exist in schema <literal>information_schema</literal> that expose some
+ of the same and additional information as mandated by the
+ <glossterm linkend="glossary-sql-standard">SQL standard</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="ddl-schemas"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-table">
+ <glossterm>Table</glossterm>
+ <glossdef>
+ <para>
+ A collection of <glossterm linkend="glossary-tuple">tuples</glossterm> having
+ a common data structure (the same number of
+ <glossterm linkend="glossary-attribute">attributes</glossterm>, in the same
+ order, having the same name and type per position).
+ A table is the most common form of
+ <glossterm linkend="glossary-relation">Relation</glossterm> in
+ <productname>PostgreSQL</productname>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createtable"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-tablespace">
+ <glossterm>Tablespace</glossterm>
+ <glossdef>
+ <para>
+ A named location on the server filesystem.
+ All <glossterm linkend="glossary-sql-object">SQL objects</glossterm>
+ which require storage beyond their definition in the
+ <glossterm linkend="glossary-system-catalog">system catalog</glossterm>
+ 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 <literal>pg_default</literal>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="manage-ag-tablespaces"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-temporary-table">
+ <glossterm>Temporary Table</glossterm>
+ <glossdef>
+ <para>
+ <glossterm linkend="glossary-table">Tables</glossterm> that exist either
+ for the lifetime of a
+ <glossterm linkend="glossary-session">session</glossterm> or a
+ <glossterm linkend="glossary-transaction">transaction</glossterm>, as
+ specified at the time of creation.
+ The data in them is not visible to other sessions, and is not
+ <glossterm linkend="glossary-logged">logged</glossterm>.
+ Temporary tables are often used to store intermediate data for a
+ multi-step operation.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createtable"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-transaction">
+ <glossterm>Transaction</glossterm>
+ <glossdef>
+ <para>
+ A combination of commands that must act as a single
+ <glossterm linkend="glossary-atomic">atomic</glossterm> command: they all
+ succeed or all fail as a single unit, and their effects are not visible to
+ other <glossterm linkend="glossary-session">sessions</glossterm> until
+ the transaction is complete, and possibly even later, depending on the
+ isolation level.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="transaction-iso"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-trigger">
+ <glossterm>Trigger</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-function">function</glossterm> which can
+ be defined to execute whenever a certain operation (<command>INSERT</command>,
+ <command>UPDATE</command>, <command>DELETE</command>,
+ <command>TRUNCATE</command>) is applied to a
+ <glossterm linkend="glossary-relation">relation</glossterm>.
+ A Trigger executes within the same
+ <glossterm linkend="glossary-transaction">transaction</glossterm> as the
+ statement which invoked it, and if the function fails, then the invoking
+ statement also fails.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createtrigger"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-tuple">
+ <glossterm>Tuple</glossterm>
+ <glossdef>
+ <para>
+ A collection of <glossterm linkend="glossary-attribute">attributes</glossterm>
+ in a fixed order.
+ That order may be defined by the <glossterm linkend="glossary-table">table</glossterm>
+ where the tuple is contained, in which case the tuple is often called a
+ <firstterm>row</firstterm>. It may also be defined by the structure of a
+ result set, in which case it is sometimes called a <firstterm>record</firstterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-unique-constraint">
+ <glossterm>Unique Constraint</glossterm>
+ <glossdef>
+ <para>
+ A type of <glossterm linkend="glossary-constraint">constraint</glossterm>
+ defined on a <glossterm linkend="glossary-relation">relation</glossterm>
+ 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.
+ </para>
+ <para>
+ Because <glossterm linkend="glossary-null">null values</glossterm> are
+ not considered equal to each other, multiple rows with null values are
+ allowed to exist without violating the unique constraint.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-unlogged">
+ <glossterm>Unlogged</glossterm>
+ <glossdef>
+ <para>
+ The property of certain <glossterm linkend="glossary-relation">relations</glossterm>
+ that the changes to them are not reflected in the
+ <glossterm linkend="glossary-wal">WAL</glossterm>.
+ This disables replication and crash recovery for these relations.
+ </para>
+ <para>
+ The primary use of unlogged tables is for storing
+ transient work data that must be shared across processes.
+ </para>
+ <para>
+ <glossterm linkend="glossary-temporary-table">Temporary tables</glossterm>
+ are always unlogged.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-update">
+ <glossterm>Update</glossterm>
+ <glossdef>
+ <para>
+ A <acronym>SQL</acronym> command used to modify
+ <glossterm linkend="glossary-tuple">rows</glossterm>
+ that may already exist in a specified <glossterm linkend="glossary-table">table</glossterm>.
+ It cannot create or remove rows.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-update"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-user">
+ <glossterm>User</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-role">role</glossterm> that has the
+ <literal>LOGIN</literal> privilege.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-user-mapping">
+ <glossterm>User mapping</glossterm>
+ <glossdef>
+ <para>
+ The translation of login credentials in the local
+ <glossterm linkend="glossary-database">database</glossterm> to credentials
+ in a remote data system defined by a
+ <glossterm linkend="glossary-foreign-data-wrapper">foreign data wrapper</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createusermapping"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-vacuum">
+ <glossterm>Vacuum</glossterm>
+ <glossdef>
+ <para>
+ The process of removing outdated <glossterm linkend="glossary-tuple">tuple
+ versions</glossterm> from tables, and other closely related
+ garbage-collection-like processing required by <productname>PostgreSQL</productname>'s
+ implementation of <glossterm linkend="glossary-mvcc">MVCC</glossterm>.
+ This can be initiated through the use of
+ the <command>VACUUM</command> command, but can also be handled automatically
+ via <glossterm linkend="glossary-autovacuum">autovacuum</glossterm> processes.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="routine-vacuuming"/> .
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-view">
+ <glossterm>View</glossterm>
+ <glossdef>
+ <para>
+ A <glossterm linkend="glossary-relation">relation</glossterm> that is defined by a
+ <command>SELECT</command> 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.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="sql-createview"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-wal-archiver">
+ <glossterm>WAL Archiver (process)</glossterm>
+ <glossdef>
+ <para>
+ A process that saves copies of <glossterm linkend="glossary-wal-file">WAL files</glossterm>
+ for the purposes of creating backups or keeping
+ <glossterm linkend="glossary-replica">replicas</glossterm> current.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="continuous-archiving"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-wal-file">
+ <glossterm>WAL File</glossterm>
+ <glossdef>
+ <para>
+ Also known as <firstterm>WAL segment</firstterm> or
+ <firstterm>WAL segment file</firstterm>.
+ Each of the sequentially-numbered files that provide storage space for
+ <glossterm linkend="glossary-wal">WAL</glossterm>.
+ 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.
+ </para>
+ <para>
+ Each WAL file can be released after a
+ <glossterm linkend="glossary-checkpoint">checkpoint</glossterm>
+ 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
+ <firstterm>recycling</firstterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="wal-internals"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>WAL</glossterm>
+ <glosssee otherterm="glossary-wal" />
+ </glossentry>
+
+ <glossentry id="glossary-wal-record">
+ <glossterm>WAL Record</glossterm>
+ <glossdef>
+ <para>
+ A low-level description of an individual data change.
+ It contains sufficient information for the data change to be
+ re-executed (<firstterm>replayed</firstterm>) in case a system failure
+ causes the change to be lost.
+ WAL records use a non-printable binary format.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="wal-internals"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry>
+ <glossterm>WAL Segment</glossterm>
+ <glosssee otherterm="glossary-wal-file" />
+ </glossentry>
+
+ <glossentry id="glossary-wal-writer">
+ <glossterm>WAL Writer (process)</glossterm>
+ <glossdef>
+ <para>
+ A process that writes <glossterm linkend="glossary-wal-record">WAL records</glossterm>
+ from <glossterm id="linkend-shared-memory">shared memory</glossterm> to
+ <glossterm id="linkend-wal-file">WAL files</glossterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="runtime-config-wal"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-window-function">
+ <glossterm>Window Function</glossterm>
+ <glossdef>
+ <para>
+ A type of <glossterm linkend="glossary-function">function</glossterm> whose
+ result is based on values found in
+ <glossterm linkend="glossary-tuple">rows</glossterm> of the same
+ <glossterm linkend="glossary-partition">partition</glossterm>.
+ All <glossterm linkend="glossary-aggregate">aggregate functions</glossterm>
+ 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 <firstterm>analytic functions</firstterm>.
+ </para>
+ <para>
+ For more information, see
+ <xref linkend="tutorial-window"/>.
+ </para>
+ </glossdef>
+ </glossentry>
+
+ <glossentry id="glossary-wal">
+ <glossterm>Write-Ahead Log</glossterm>
+ <glossdef>
+ <para>
+ The journal that keeps track of the changes in the
+ <glossterm linkend="glossary-instance">instance</glossterm> as user- and
+ system-invoked operations take place.
+ It comprises many individual
+ <glossterm linkend="glossary-wal-record">WAL records</glossterm> written
+ sequentially to <glossterm linkend="glossary-wal-file">WAL files</glossterm>.
+ </para>
+ </glossdef>
+ </glossentry>
+ </glosslist>
+</appendix>
index 1f7bd3287848292ee9326d5483b1291af7495621..ba3d6261029a476c8cc86f55cea64f07baf79636 100644 (file)
&docguide;
&limits;
&acronyms;
+ &glossary;
&color;
</part>