diff --git a/doc/src/sgml/filelist.sgml b/doc/src/sgml/filelist.sgml index 1043d0f7ab..cf21ef857e 100644 --- a/doc/src/sgml/filelist.sgml +++ b/doc/src/sgml/filelist.sgml @@ -170,6 +170,7 @@ + diff --git a/doc/src/sgml/glossary.sgml b/doc/src/sgml/glossary.sgml new file mode 100644 index 0000000000..7d981a9223 --- /dev/null +++ b/doc/src/sgml/glossary.sgml @@ -0,0 +1,1692 @@ + + 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 (process) + + + A set of background processes that routinely perform + vacuum + and analyze + operations. + + + For more information, see + . + + + + + + Backend (process) + + + Processes 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) + + + Individual processes within an instance, + which run system- or user-supplied code. + They provide infrastructure for several features in + PostgreSQL, such as + logical replication + and parallel queries. + Extensions can add + custom background worker processes, as well. + + + 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, instead of generating fewer 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. + + + + + + Catalog + + + The SQL standard uses this term to + indicate what is called a + Database in + PostgreSQL's terminology. + + + This should not be confused with the + 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 process that writes dirty pages to the file system and creates a special + checkpoint WAL record. 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. + + + + + + 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. + + + 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. + + + + + + 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 fixed + 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 + Heap or + Index object. + File Segments are + limited in size by a configuration value and if that size is exceeded, it + will be split into multiple physical files. + + + 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 Roles to access + specific objects within the Database. + + + For more information, see + . + + + + + + Heap + + + Contains the values of Row + attributes (i.e. the data). The Heap + is realized within Database files. + + + + + + Host + + + + + 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 act of storing information rather than just the method of accessing + the information. This term is used in Materialized + Views, meaning that the data derived from the + View is actually stored on disk separately from + the sources of that data. When using the term + Materialized to refer to + multi-step queries, it means that the data of a given step is stored + in memory, but that storage may spill over onto disk. + + + + + + Materialized View + + + A Relation that is defined in the same way that + 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 + + + In reference to a Table: + A Table that can be queried directly, + or via a partitioned table, which is a collection of + sub-tables, each capable of holding one defined + subset of information that does not overlap with any other + table in the collection. + + + + + In reference to a window function: + a partition is a definition that identifies which neighboring + Rows can be considered by the + function. + + + + + + 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 may seem + 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 + Users and Roles. + + + For more information, see + . + + + + + + Role + + + A collection of access privileges to the + Database. 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. + + + 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. + + + Many SQL Objects reside in the default + Schema public, but it is + expected that more 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 query a Database. + Normally, SELECTs 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 + . + + + + + + Serializable + + + Transactions defined as SERIALIZABLE are unable to + see changes made within other transactions. In effect, for the + initializing session the entire Database + appears to be frozen for the duration of the + Transaction. + + + + + + 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. + + + + + + Sequence + + + A Database object which + represents the mathematical concept of a numerical integral sequence. + It can be thought of as a Table + with exactly one Row and + one Column. The + value stored is known as the current value. A + Sequence has a defined + direction (usually increasing) and an interval step (usually 1). + Whenever the NEXTVAL pseudo-column of a + Sequence 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 + Sequence are never + reverted, even in the case of a + Rollback, which means + that the Sequence + will never generate the same number twice, which makes it useful for + generating + Primary Key values. + + + For more information, see + . + + + + + + Shared Memory + + + RAM which is used by the processes common to an + Instance. It mirrors parts of + Database files, provides an area for + WAL Records, and stores additional common + information. Note that Shared Memory belongs to + the complete Instance, not to a single + Database. + + + Shared Memory is organized into pages. If 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 + . + + + + + + Stats Collector + + + This process collects statistical information about the + Cluster's activities. + + + For more information, see + . + + + + + + System Catalog + + + A collection of Tables and + Views which describe the structure of all + SQL objects of the Database + and the Global SQL Objects of the + Cluster. The System + Catalog resides in the schema + pg_catalog. Main parts are mirrored as + Views in the Schema + information_schema. + + + 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 + PostgreSQL. + + + 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. + + + 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. + + + 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 found, in which case the + Tuple is often called a + row or record. + It may also be defined by the structure of a + Result Set. + + + + + + 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 + + + Changes to an unlogged Relation + 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 is said to be a User. + + + + + + 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 that 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 numerically-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. + + + + + diff --git a/doc/src/sgml/postgres.sgml b/doc/src/sgml/postgres.sgml index 1f7bd32878..ba3d626102 100644 --- a/doc/src/sgml/postgres.sgml +++ b/doc/src/sgml/postgres.sgml @@ -278,6 +278,7 @@ &docguide; &limits; &acronyms; + &glossary; &color;