| System CatalogsNameThe System Catalogs -- The System catalogs are where a relational database management system stores schema metadata,
such as information about tables and columns, and internal bookkeeping information.
Overview Table 1 lists the System catalogs.
More detailed documentation of each catalog follows below.
Most system catalogs are copied from the template database during
database creation and are thereafter database-specific. A few
catalogs are physically shared across all databases in a cluster;
these are marked in the descriptions of the individual catalogs.
Table 1. The System Catalogs edb_package The catalog edb_package stores information about
packages.
Table 2. edb_package Columns Name | Type | References | Description |
---|
pkgname | name | | Name of the package | pkgnamespace | oid | pg_namespace.oid | The OID of the namespace that contains this relation | pkgowner | oid | pg_shadow.usesysid | Owner of the relation | pkgheadsrc | text | | The Package definition source | pkgbodysrc | text | | The Package body source | pkgproperties | char | | The properties of a package as a whole. This column is reserved for
future purposes and is currently always set to "P". | pkgacl | aclitem[] | | Access privileges; see the descriptions of GRANT and REVOKE for details. |
edb_pkgelements The catalog edb_pkgelements stores information about
the possible elements that can be contained in a package. The possible values
elements include functions, stored procedures and variables. There is one
row for each package element that is a member of a package.
Table 3. edb_pkgelements Columns Name | Type | References | Description |
---|
packageoid | oid | edb_package.oid | The OID of the package that contains this package element. | eltname | name | | The name of the package element. Possible package elements include
stored procedures, functions and variables. | visibility | char | | Access privileges for a package element. Possible values are
+ and - representing
public and private access
privileges. | etlclass | char | | The type of the package element. Possible values are
P,F and V
standing for stored procedures,
functions and variables. | etldatatype | oid | | OID of the data type of the package element.
In case of a variable, this OID is the OID of data type of the variable, whereas in
case of a function and/or stored procedure, this is the OID of the return type of
the function and stored procedure (this OID is always 1700, i.e. void for a stored
procedure). | nargs | int2 | | The number of arguments for this package element. This information
is only applicable if the package element is a stored procedure or
function. | argtypes | oidvector[] | | An array with the data types of the package element arguments.
This information is only applicable if the package element is a stored procedure or
function.
| allargtypes | oid[] | pg_type.oid | An array with the data types of the function and/or stored
procedure arguments.
This includes all arguments (including OUT and INOUT arguments);
however, if all the arguments are IN arguments, this field will be null. | argmodes | char[] | | An array with the modes of the function/stored procedure arguments,
encoded as i for IN arguments, o for OUT arguments,
b for INOUT arguments. If all the arguments are IN arguments,
this field will be null. | argnames | text[] | | An array with the names of the function/stored procedure arguments.
Arguments without a name are set to empty strings in the array.
If none of the arguments have a name, this field will be null. |
pg_aggregate The catalog pg_aggregate stores information about
aggregate functions. An aggregate function is a function that
operates on a set of values (typically one column from each row
that matches a query condition) and returns a single value computed
from all these values. Typical aggregate functions are
sum , count , and
max . Each entry in
pg_aggregate is an extension of an entry
in pg_proc. The pg_proc
entry carries the aggregate's name, input and output data types, and
other information that is similar to ordinary functions.
Table 4. pg_aggregate Columns Name | Type | References | Description |
---|
aggfnoid | regproc | pg_proc.oid | pg_proc OID of the aggregate function | aggtransfn | regproc | pg_proc.oid | Transition function | aggfinalfn | regproc | pg_proc.oid | Final function (zero if none) | aggtranstype | oid | pg_type.oid | The type of the aggregate function's internal transition (state) data | agginitval | text | | The initial value of the transition state. This is a text
field containing the initial value in its external string
representation. If the value is null, the transition state
value starts out null.
|
New aggregate functions are registered with the CREATE
AGGREGATE command.
pg_am The catalog pg_am stores information about index access
methods. There is one row for each index access method supported by
the system.
Table 5. pg_am Columns Name | Type | References | Description |
---|
amname | name | | Name of the access method | amowner | int4 | pg_shadow.usesysid | User ID of the owner (currently not used) | amstrategies | int2 | | Number of operator strategies for this access method | amsupport | int2 | | Number of support routines for this access method | amorderstrategy | int2 | | Zero if the index offers no sort order, otherwise the strategy
number of the strategy operator that describes the sort order | amcanunique | bool | | Does the access method support unique indexes? | amcanmulticol | bool | | Does the access method support multicolumn indexes? | amindexnulls | bool | | Does the access method support null index entries? | amconcurrent | bool | | Does the access method support concurrent updates? | amgettuple | regproc | pg_proc.oid | "Next valid tuple" function | aminsert | regproc | pg_proc.oid | "Insert this tuple" function | ambeginscan | regproc | pg_proc.oid | "Start new scan" function | amrescan | regproc | pg_proc.oid | "Restart this scan" function | amendscan | regproc | pg_proc.oid | "End this scan" function | ammarkpos | regproc | pg_proc.oid | "Mark current scan position" function | amrestrpos | regproc | pg_proc.oid | "Restore marked scan position" function | ambuild | regproc | pg_proc.oid | "Build new index" function | ambulkdelete | regproc | pg_proc.oid | Bulk-delete function | amvacuumcleanup | regproc | pg_proc.oid | Post-VACUUM cleanup function | amcostestimate | regproc | pg_proc.oid | Function to estimate cost of an index scan |
An index access method that supports multiple columns (has
amcanmulticol true) must
support indexing null values in columns after the first, because the planner
will assume the index can be used for queries on just the first
column(s). For example, consider an index on (a,b) and a query with
WHERE a = 4. The system will assume the index can be used to scan for
rows with a = 4, which is wrong if the index omits rows where b is null.
It is, however, OK to omit rows where the first indexed column is null.
(GiST currently does so.)
amindexnulls should be set true only if the
index access method indexes all rows, including arbitrary combinations of null values.
pg_amop The catalog pg_amop stores information about operators
associated with index access method operator classes. There is one
row for each operator that is a member of an operator class.
Table 6. pg_amop Columns Name | Type | References | Description |
---|
amopclaid | oid | pg_opclass.oid | The index operator class this entry is for | amopsubtype | oid | pg_type.oid | Subtype to distinguish multiple entries for one strategy;
zero for default | amopstrategy | int2 | | Operator strategy number | amopreqcheck | bool | | Index hit must be rechecked | amopopr | oid | pg_operator.oid | OID of the operator |
pg_amproc The catalog pg_amproc stores information about support
procedures
associated with index access method operator classes. There is one
row for each support procedure belonging to an operator class.
Table 7. pg_amproc Columns Name | Type | References | Description |
---|
amopclaid | oid | pg_opclass.oid | The index operator class this entry is for | amprocsubtype | oid | pg_type.oid | Subtype, if cross-type routine, else zero | amprocnum | int2 | | Support procedure number | amproc | regproc | pg_proc.oid | OID of the procedure |
pg_attrdef The catalog pg_attrdef stores column default values. The main information
about columns is stored in pg_attribute
(see below). Only columns that explicitly specify a default value
(when the table is created or the column is added) will have an
entry here.
Table 8. pg_attrdef Columns Name | Type | References | Description |
---|
adrelid | oid | pg_class.oid | The table this column belongs to | adnum | int2 | pg_attribute.attnum | The number of the column | adbin | text | | The internal representation of the column default value | adsrc | text | | A human-readable representation of the default value |
pg_attribute The catalog pg_attribute stores information about
table columns. There will be exactly one
pg_attribute row for every column in every
table in the database. (There will also be attribute entries for
indexes and other objects. See pg_class.)
The term attribute is equivalent to column and is used for
historical reasons.
Table 9. pg_attribute Columns Name | Type | References | Description |
---|
attrelid | oid | pg_class.oid | The table this column belongs to | attname | name | | The column name | atttypid | oid | pg_type.oid | The data type of this column | attstattarget | int4 | | attstattarget controls the level of detail
of statistics accumulated for this column by
ANALYZE.
A zero value indicates that no statistics should be collected.
A negative value says to use the system default statistics target.
The exact meaning of positive values is data type-dependent.
For scalar data types, attstattarget
is both the target number of "most common values"
to collect, and the target number of histogram bins to create.
| attlen | int2 | | A copy of pg_type.typlen of this column's
type
| attnum | int2 | | The number of the column. Ordinary columns are numbered from 1
up. System columns, such as oid,
have (arbitrary) negative numbers.
| attndims | int4 | | Number of dimensions, if the column is an array type; otherwise 0.
(Presently, the number of dimensions of an array is not enforced,
so any nonzero value effectively means "it's an array".)
| attcacheoff | int4 | | Always -1 in storage, but when loaded into a row descriptor
in memory this may be updated to cache the offset of the attribute
within the row.
| atttypmod | int4 | | atttypmod records type-specific data
supplied at table creation time (for example, the maximum
length of a varchar column). It is passed to
type-specific input functions and length coercion functions.
The value will generally be -1 for types that do not need atttypmod.
| attbyval | bool | | A copy of pg_type.typbyval of this column's type
| attstorage | char | | Normally a copy of pg_type.typstorage of this
column's type. For TOAST-able data types, this can be altered
after column creation to control storage policy.
| attalign | char | | A copy of pg_type.typalign of this column's type
| attnotnull | bool | | This represents a not-null constraint. It is possible to
change this column to enable or disable the constraint.
| atthasdef | bool | | This column has a default value, in which case there will be a
corresponding entry in the pg_attrdef
catalog that actually defines the value.
| attisdropped | bool | | This column has been dropped and is no longer valid. A dropped
column is still physically present in the table, but is
ignored by the parser and so cannot be accessed via SQL.
| attislocal | bool | | This column is defined locally in the relation. Note that a column may
be locally defined and inherited simultaneously.
| attinhcount | int4 | | The number of direct ancestors this column has. A column with a
nonzero number of ancestors cannot be dropped nor renamed.
|
pg_authid The catalog pg_authid contains information about
database authorization identifiers (roles). A role subsumes the concepts
of "users" and "groups". A user is essentially just a
role with the rolcanlogin flag set. Any role (with or
without rolcanlogin) may have other roles as members; see
pg_auth_members.
Since this catalog contains passwords, it must not be publicly readable.
pg_roles
is a publicly readable view on
pg_authid that blanks out the password field.
Chapter 31> contains detailed information about user and
privilege management.
Because user identities are cluster-wide,
pg_authid
is shared across all databases of a cluster: there is only one
copy of pg_authid per cluster, not
one per database.
Table 10. pg_authid Columns Name | Type | References | Description |
---|
rolname | name | | Role name | rolsuper | bool | | Role has superuser privileges | rolinherit | bool | | Role automatically inherits privileges of roles it is a
member of | rolcreaterole | bool | | Role may create more roles | rolcreatedb | bool | | Role may create databases | rolcatupdate | bool | | Role may update system catalogs directly. (Even a superuser may not do
this unless this column is true.)
| rolcanlogin | bool | | Role may log in, that is, this role can be given as the initial
session authorization identifier.
| rolconnlimit | int4 | | For roles that can log in, this sets maximum number of concurrent
connections this role can make. -1 means no limit.
| rolpassword | text | | Password (possibly encrypted); NULL if none | rolvaliduntil | timestamptz | | Password expiry time (only used for password authentication);
NULL if no expiration | rolconfig | text[] | | Session defaults for run-time configuration variables |
pg_auth_members The catalog pg_auth_members shows the membership
relations between roles. Any non-circular set of relationships is allowed.
Because user identities are cluster-wide,
pg_auth_members
is shared across all databases of a cluster: there is only one
copy of pg_auth_members per cluster, not
one per database.
Table 11. pg_auth_members Columns Name | Type | References | Description |
---|
roleid | oid | pg_authid.oid | ID of a role that has a member | member | oid | pg_authid.oid | ID of a role that is a member of roleid | grantor | oid | pg_authid.oid | ID of the role that granted this membership | admin_option | bool | | True if member may grant membership in
roleid to others |
pg_autovacuum The catalog pg_autovacuum stores optional
per-relation configuration parameters relevant to autovacuuming.
If there is an entry here for a particular relation, the given
parameters will be used for autovacuuming that table. If no entry
is present, the system-wide defaults will be used.
Table 12. pg_autovacuum Columns Name | Type | References | Description |
---|
vacrelid | oid | pg_class.oid | The table this entry is for | enabled | bool | | If false, this table is never autovacuumed | vac_base_thresh | integer | | Minimum number of modified tuples before vacuum | vac_scale_factor | float4 | | Multiplier for reltuples to add to
vac_base_thresh | anl_base_thresh | integer | | Minimum number of modified tuples before analyze | anl_scale_factor | float4 | | Multiplier for reltuples to add to
anl_base_thresh | vac_cost_delay | integer | | Custom vacuum_cost_delay parameter | vac_cost_limit | integer | | Custom vacuum_cost_limit parameter |
The autovacuum daemon will initiate a VACUUM operation
on a particular table when the number of updated or deleted tuples
exceeds vac_base_thresh plus
vac_scale_factor times the number of
live tuples currently estimated to be in the relation.
Similarly, it will initiate an ANALYZE operation
when the number of inserted, updated or deleted tuples
exceeds anl_base_thresh plus
anl_scale_factor times the number of
live tuples currently estimated to be in the relation.
Any of the numerical fields can contain -1 (or indeed
any negative value) to indicate that the system-wide default should
be used for this particular value. Observe that the
vac_cost_delay variable inherits its default value from the
autovacuum_vacuum_cost_delay configuration parameter,
or from vacuum_cost_delay if the former is set to a negative
value. The same applies to vac_cost_limit.
pg_cast The catalog pg_cast stores data type conversion paths,
both built-in paths and those defined with CREATE CAST.
Table 13. pg_cast Columns Name | Type | References | Description |
---|
castsource | oid | pg_type.oid | OID of the source data type | casttarget | oid | pg_type.oid | OID of the target data type | castfunc | oid | pg_proc.oid | The OID of the function to use to perform this cast. Zero is
stored if the data types are binary compatible (that is, no
run-time operation is needed to perform the cast).
| castcontext | char | | Indicates what contexts the cast may be invoked in.
e means only as an explicit cast (using
CAST or :: syntax).
a means implicitly in assignment
to a target column, as well as explicitly.
i means implicitly in expressions, as well as the
other cases.
|
The cast functions listed in pg_cast must
always take the cast source type as their first argument type, and
return the cast destination type as their result type. A cast
function can have up to three arguments. The second argument,
if present, must be type integer; it receives the type
modifier associated with the destination type, or -1
if there is none. The third argument,
if present, must be type boolean; it receives true
if the cast is an explicit cast, false otherwise.
It is legitimate to create a pg_cast entry
in which the source and target types are the same, if the associated
function takes more than one argument. Such entries represent
"length coercion functions" that coerce values of the type
to be legal for a particular type modifier value. Note however that
at present there is no support for associating non-default type
modifiers with user-created data types, and so this facility is only
of use for the small number of built-in types that have type modifier
syntax built into the grammar.
When a pg_cast entry has different source and
target types and a function that takes more than one argument, it
represents converting from one type to another and applying a length
coercion in a single step. When no such entry is available, coercion
to a type that uses a type modifier involves two steps, one to
convert between datatypes and a second to apply the modifier.
pg_class The catalog pg_class catalogs tables and most
everything else that has columns or is otherwise similar to a
table. This includes indexes (but see also
pg_index), sequences, views, composite types,
and some kinds of special relation; see relkind.
Below, when we mean all of these
kinds of objects we speak of "relations". Not all
columns are meaningful for all relation types.
Table 14. pg_class Columns Name | Type | References | Description |
---|
relname | name | | Name of the table, index, view, etc. | relnamespace | oid | pg_namespace.oid | The OID of the namespace that contains this relation
| reltype | oid | pg_type.oid | The OID of the data type that corresponds to this table's rowtype,
if any (zero for indexes, which have no pg_type entry)
| relowner | int4 | pg_shadow.usesysid | Owner of the relation | relam | oid | pg_am.oid | If this is an index, the access method used (B-tree, hash, etc.) | relfilenode | oid | | Name of the on-disk file of this relation; 0 if none | reltablespace | oid | pg_tablespace.oid | The tablespace in which this relation is stored. If zero,
the database's default tablespace is implied. (Not meaningful
if the relation has no on-disk file.)
| relpages | int4 | | Size of the on-disk representation of this table in pages (of size
BLCKSZ).
This is only an estimate used by the planner.
It is updated by VACUUM,
ANALYZE, and a few DDL commands
such as CREATE INDEX.
| reltuples | float4 | | Number of rows in the table.
This is only an estimate used by the planner.
It is updated by VACUUM,
ANALYZE, and a few DDL commands
such as CREATE INDEX.
| reltoastrelid | oid | pg_class.oid | OID of the TOAST table associated with this table, 0 if none.
The TOAST table stores large attributes "out of
line" in a secondary table.
| reltoastidxid | oid | pg_class.oid | For a TOAST table, the OID of its index. 0 if not a TOAST table.
| relhasindex | bool | | True if this is a table and it has (or recently had) any
indexes. This is set by CREATE INDEX, but
not cleared immediately by DROP INDEX.
VACUUM clears relhasindex if it finds the
table has no indexes.
| relisshared | bool | | True if this table is shared across all databases in the
cluster. Only certain system catalogs (such as
pg_database) are shared. | relkind | char | | r = ordinary table, i = index,
S = sequence, v = view, c =
composite type, s = special, t = TOAST
table
| relnatts | int2 | | Number of user columns in the relation (system columns not
counted). There must be this many corresponding entries in
pg_attribute. See also
pg_attribute.attnum.
| relchecks | int2 | | Number of check constraints on the table; see
pg_constraint catalog
| reltriggers | int2 | | Number of triggers on the table; see
pg_trigger catalog
| relukeys | int2 | | unused (not the number of unique keys) | relfkeys | int2 | | unused (not the number of foreign keys on the table) | relrefs | int2 | | unused | relhasoids | bool | | True if we generate an OID for each row of the relation.
| relhaspkey | bool | | True if the table has (or once had) a primary key.
| relhasrules | bool | | Table has rules; see
pg_rewrite catalog
| relhassubclass | bool | | At least one table inherits from this one | relacl | aclitem[] | | Access privileges; see the descriptions of
GRANT and REVOKE for
details.
|
pg_constraint The catalog pg_constraint stores check, primary key, unique, and foreign
key constraints on tables. (Column constraints are not treated
specially. Every column constraint is equivalent to some table
constraint.) Not-null constraints are represented in the
pg_attribute catalog.
Check constraints on domains are stored here, too.
Table 15. pg_constraint Columns Name | Type | References | Description |
---|
conname | name | | Constraint name (not necessarily unique!) | connamespace | oid | pg_namespace.oid | The OID of the namespace that contains this constraint
| contype | char | | c = check constraint,
f = foreign key constraint,
p = primary key constraint,
u = unique constraint
| condeferrable | bool | | Is the constraint deferrable? | condeferred | bool | | Is the constraint deferred by default? | conrelid | oid | pg_class.oid | The table this constraint is on; 0 if not a table constraint | contypid | oid | pg_type.oid | The domain this constraint is on; 0 if not a domain constraint | confrelid | oid | pg_class.oid | If a foreign key, the referenced table; else 0 | confupdtype | char | | Foreign key update action code | confdeltype | char | | Foreign key deletion action code | confmatchtype | char | | Foreign key match type | conkey | int2[] | pg_attribute.attnum | If a table constraint, list of columns which the constraint constrains | confkey | int2[] | pg_attribute.attnum | If a foreign key, list of the referenced columns | conbin | text | | If a check constraint, an internal representation of the expression | consrc | text | | If a check constraint, a human-readable representation of the expression |
Note: consrc is not updated when referenced objects
change; for example, it won't track renaming of columns. Rather than
relying on this field, it's best to use pg_get_constraintdef()
to extract the definition of a check constraint.
Note: pg_class.relchecks needs to agree with the
number of check-constraint entries found in this table for the
given relation.
pg_conversion The catalog pg_conversion stores encoding conversion information. See
CREATE CONVERSION for more information.
Table 16. pg_conversion Columns Name | Type | References | Description |
---|
conname | name | | Conversion name (unique within a namespace) | connamespace | oid | pg_namespace.oid | The OID of the namespace that contains this conversion
| conowner | int4 | pg_shadow.usesysid | Owner of the conversion | conforencoding | int4 | | Source encoding ID | contoencoding | int4 | | Destination encoding ID | conproc | regproc | pg_proc.oid | Conversion procedure | condefault | bool | | True if this is the default conversion |
pg_database The catalog pg_database stores information
about the available databases. Databases are created with the
CREATE DATABASE command. Consult
Chapter 32 for details about the meaning of some of the
parameters.
Unlike most system catalogs, pg_database
is shared across all databases of a cluster: there is only one
copy of pg_database per cluster, not
one per database.
Table 17. pg_database Columns Name | Type | References | Description |
---|
datname | name | | Database name | datdba | int4 | pg_shadow.usesysid | Owner of the database, usually the user who created it | encoding | int4 | | Character encoding for this database | datistemplate | bool | | If true then this database can be used in the
TEMPLATE clause of CREATE
DATABASE to create a new database as a clone of
this one.
| datallowconn | bool | | If false then no one can connect to this database. This is
used to protect the template0 database from being altered.
| datlastsysoid | oid | | Last system OID in the database; useful
particularly to pg_dump
| datvacuumxid | xid | | All rows inserted or deleted by transaction IDs before this one
have been marked as known committed or known aborted in this database.
This is used to determine when commit-log space can be recycled.
| datfrozenxid | xid | | All rows inserted by transaction IDs before this one have been
relabeled with a permanent ("frozen") transaction ID in this
database. This is useful to check whether a database must be vacuumed
soon to avoid transaction ID wrap-around problems.
| dattablespace | oid | pg_tablespace.oid | The default tablespace for the database.
Within this database, all tables for which
pg_class.reltablespace is zero
will be stored in this tablespace; in particular, all the non-shared
system catalogs will be there.
| datconfig | text[] | | Session defaults for run-time configuration variables | datacl | aclitem[] | | Access privileges |
pg_depend The catalog pg_depend records the dependency
relationships between database objects. This information allows
DROP commands to find which other objects must be dropped
by DROP CASCADE or prevent dropping in the DROP
RESTRICT case.
Table 18. pg_depend Columns Name | Type | References | Description |
---|
classid | oid | pg_class.oid | The OID of the system catalog the dependent object is in | objid | oid | any OID column | The OID of the specific dependent object | objsubid | int4 | | For a table column, this is the column number (the
objid and classid refer to the
table itself). For all other object types, this column is
zero.
| refclassid | oid | pg_class.oid | The OID of the system catalog the referenced object is in | refobjid | oid | any OID column | The OID of the specific referenced object | refobjsubid | int4 | | For a table column, this is the column number (the
refobjid and refclassid refer
to the table itself). For all other object types, this column
is zero.
| deptype | char | | A code defining the specific semantics of this dependency relationship; see text.
|
In all cases, a pg_depend entry indicates that the
referenced object may not be dropped without also dropping the dependent
object. However, there are several subflavors identified by
deptype:
- DEPENDENCY_NORMAL (n)
A normal relationship between separately-created objects. The
dependent object may be dropped without affecting the
referenced object. The referenced object may only be dropped
by specifying CASCADE, in which case the dependent
object is dropped, too. Example: a table column has a normal
dependency on its data type.
- DEPENDENCY_AUTO (a)
The dependent object can be dropped separately from the
referenced object, and should be automatically dropped
(regardless of RESTRICT or CASCADE
mode) if the referenced object is dropped. Example: a named
constraint on a table is made autodependent on the table, so
that it will go away if the table is dropped.
- DEPENDENCY_INTERNAL (i)
The dependent object was created as part of creation of the
referenced object, and is really just a part of its internal
implementation. A DROP of the dependent object
will be disallowed outright (we'll tell the user to issue a
DROP against the referenced object, instead). A
DROP of the referenced object will be propagated
through to drop the dependent object whether
CASCADE is specified or not. Example: a trigger
that's created to enforce a foreign-key constraint is made
internally dependent on the constraint's
pg_constraint entry.
- DEPENDENCY_PIN (p)
There is no dependent object; this type of entry is a signal
that the system itself depends on the referenced object, and so
that object must never be deleted. Entries of this type are
created only by initdb. The columns for the
dependent object contain zeroes.
Other dependency flavors may be needed in future.
pg_description The catalog pg_description can store an optional description or
comment for each database object. Descriptions can be manipulated
with the COMMENT command and viewed with
psql's \d commands.
Descriptions of many built-in system objects are provided in the initial
contents of pg_description.
Table 19. pg_description Columns Name | Type | References | Description |
---|
objoid | oid | any OID column | The OID of the object this description pertains to | classoid | oid | pg_class.oid | The OID of the system catalog this object appears in | objsubid | int4 | | For a comment on a table column, this is the column number (the
objoid and classoid refer to
the table itself). For all other object types, this column is
zero.
| description | text | | Arbitrary text that serves as the description of this object. |
pg_group The catalog pg_group defines groups and stores what users belong to what
groups. Groups are created with the CREATE
GROUP command. Consult Chapter 31 for information
about user privilege management.
Because user and group identities are cluster-wide,
pg_group
is shared across all databases of a cluster: there is only one
copy of pg_group per cluster, not
one per database.
Table 20. pg_group Columns Name | Type | References | Description |
---|
groname | name | | Name of the group | grosysid | int4 | | An arbitrary number to identify this group | grolist | int4[] | pg_shadow.usesysid | An array containing the IDs of the users in this group |
pg_index The catalog pg_index contains part of the information
about indexes. The rest is mostly in
pg_class.
Table 21. pg_index Columns Name | Type | References | Description |
---|
indexrelid | oid | pg_class.oid | The OID of the pg_class entry for this index | indrelid | oid | pg_class.oid | The OID of the pg_class entry for the table this index is for | indkey | int2vector | pg_attribute.attnum | This is an array of indnatts (up to
INDEX_MAX_KEYS) values that indicate which
table columns this index indexes. For example a value of
1 3 would mean that the first and the third table
columns make up the index key. A zero in this array indicates that the
corresponding index attribute is an expression over the table columns,
rather than a simple column reference.
| indclass | oidvector | pg_opclass.oid | For each column in the index key this contains the OID of
the operator class to use. See
pg_opclass for details.
| indnatts | int2 | | The number of columns in the index (duplicates
pg_class.relnatts) | indisunique | bool | | If true, this is a unique index. | indisprimary | bool | | If true, this index represents the primary key of the table.
(indisunique should always be true when this is true.) | indisclustered | bool | | If true, the table was last clustered on this index. | indexprs | text | | Expression trees (in nodeToString() representation)
for index attributes that are not simple column references. This is a
list with one element for each zero entry in indkey.
Null if all index attributes are simple references. | indpred | text | | Expression tree (in nodeToString() representation)
for partial index predicate. Null if not a partial index. |
pg_inherits The catalog pg_inherits records information about
table inheritance hierarchies.
Table 22. pg_inherits Columns Name | Type | References | Description |
---|
inhrelid | oid | pg_class.oid | The OID of the child table.
| inhparent | oid | pg_class.oid | The OID of the parent table.
| inhseqno | int4 | | If there is more than one parent for a child table (multiple
inheritance), this number tells the order in which the
inherited columns are to be arranged. The count starts at 1.
|
pg_language The catalog pg_language registers call interfaces or
languages in which you can write functions or stored procedures.
Table 23. pg_language Columns Name | Type | References | Description |
---|
lanname | name | | Name of the language (to be specified when creating a function) | lanispl | bool | | This is false for internal languages (such as
SQL) and true for user-defined languages.
Currently, pg_dump still uses this
to determine which languages need to be dumped, but this may be
replaced by a different mechanism sometime.
| lanpltrusted | bool | | This is a trusted language. See under CREATE
LANGUAGE what this means. If this is an internal
language (lanispl is false) then
this column is meaningless.
| lanplcallfoid | oid | pg_proc.oid | For noninternal languages this references the language
handler, which is a special function that is responsible for
executing all functions that are written in the particular
language.
| lanvalidator | oid | pg_proc.oid | This references a language validator function that is responsible
for checking the syntax and validity of new functions when they
are created. See under CREATE LANGUAGE for
further information about validators.
| lanacl | aclitem[] | | Access privileges |
pg_largeobject The catalog pg_largeobject holds the data making up
"large objects". A large object is identified by an
OID assigned when it is created. Each large object is broken into
segments or "pages" small enough to be conveniently stored as rows
in pg_largeobject.
The amount of data per page is defined to be LOBLKSIZE (which is currently
BLCKSZ/4, or typically 2 kB).
Table 24. pg_largeobject Columns Name | Type | References | Description |
---|
loid | oid | | Identifier of the large object that includes this page | pageno | int4 | | Page number of this page within its large object
(counting from zero) | data | bytea | | Actual data stored in the large object.
This will never be more than LOBLKSIZE bytes and may be less.
|
Each row of pg_largeobject holds data
for one page of a large object, beginning at
byte offset (pageno * LOBLKSIZE) within the object. The implementation
allows sparse storage: pages may be missing, and may be shorter than
LOBLKSIZE bytes even if they are not the last page of the object.
Missing regions within a large object read as zeroes.
pg_listener The catalog pg_listener supports the LISTEN
and NOTIFY commands. A listener creates an entry in
pg_listener for each notification name
it is listening for. A notifier scans pg_listener
and updates each matching entry to show that a notification has occurred.
The notifier also sends a signal (using the PID recorded in the table)
to awaken the listener from sleep.
Table 25. pg_listener Columns Name | Type | References | Description |
---|
relname | name | | Notify condition name. (The name need not match any actual
relation in the database; the name relname is historical.)
| listenerpid | int4 | | PID of the server process that created this entry. | notification | int4 | | Zero if no event is pending for this listener. If an event is
pending, the PID of the server process that sent the notification.
|
pg_namespace The catalog pg_namespace stores namespaces.
A namespace is the structure underlying SQL schemas: each namespace
can have a separate collection of relations, types, etc. without name
conflicts.
Table 26. pg_namespace Columns Name | Type | References | Description |
---|
nspname | name | | Name of the namespace | nspowner | int4 | pg_shadow.usesysid | Owner of the namespace | nspacl | aclitem[] | | Access privileges |
pg_opclass The catalog pg_opclass defines
index access method operator classes. Each operator class defines
semantics for index columns of a particular data type and a particular
index access method. Note that there can be multiple operator classes
for a given data type/access method combination, thus supporting multiple
behaviors.
Table 27. pg_opclass Columns Name | Type | References | Description |
---|
opcamid | oid | pg_am.oid | Index access method operator class is for | opcname | name | | Name of this operator class | opcnamespace | oid | pg_namespace.oid | Namespace of this operator class | opcowner | int4 | pg_shadow.usesysid | Operator class owner | opcintype | oid | pg_type.oid | Data type that the operator class indexes | opcdefault | bool | | True if this operator class is the default for opcintype | opckeytype | oid | pg_type.oid | Type of data stored in index, or zero if same as opcintype |
The majority of the information defining an operator class is actually
not in its pg_opclass row, but in the associated
rows in pg_amop and
pg_amproc. Those rows are considered to be
part of the operator class definition - this is not unlike the way
that a relation is defined by a single pg_class
row plus associated rows in pg_attribute and
other tables.
pg_operator The catalog pg_operator stores information about operators. See
CREATE OPERATOR
for
details on these operator parameters.
Table 28. pg_operator Columns Name | Type | References | Description |
---|
oprname | name | | Name of the operator | oprnamespace | oid | pg_namespace.oid | The OID of the namespace that contains this operator
| oprowner | int4 | pg_shadow.usesysid | Owner of the operator | oprkind | char | | b = infix ("both"), l = prefix
("left"), r = postfix ("right")
| oprcanhash | bool | | This operator supports hash joins | oprleft | oid | pg_type.oid | Type of the left operand | oprright | oid | pg_type.oid | Type of the right operand | oprresult | oid | pg_type.oid | Type of the result | oprcom | oid | pg_operator.oid | Commutator of this operator, if any | oprnegate | oid | pg_operator.oid | Negator of this operator, if any | oprlsortop | oid | pg_operator.oid | If this operator supports merge joins, the operator that sorts
the type of the left-hand operand (L<L)
| oprrsortop | oid | pg_operator.oid | If this operator supports merge joins, the operator that sorts
the type of the right-hand operand (R<R)
| oprltcmpop | oid | pg_operator.oid | If this operator supports merge joins, the less-than operator that
compares the left and right operand types (L<R)
| oprgtcmpop | oid | pg_operator.oid | If this operator supports merge joins, the greater-than operator that
compares the left and right operand types (L>R)
| oprcode | regproc | pg_proc.oid | Function that implements this operator | oprrest | regproc | pg_proc.oid | Restriction selectivity estimation function for this operator | oprjoin | regproc | pg_proc.oid | Join selectivity estimation function for this operator |
Unused column contain zeroes, for example oprleft is zero for a
prefix operator.
pg_pltemplate The catalog pg_pltemplate stores
"template" information for procedural languages.
A template for a language allows the language to be created in a
particular database by a simple CREATE LANGUAGE command,
with no need to specify implementation details.
Unlike most system catalogs, pg_pltemplate
is shared across all databases of a cluster: there is only one
copy of pg_pltemplate per cluster, not
one per database. This allows the information to be accessible in
each database as it is needed.
Table 29. pg_pltemplate Columns Name | Type | References | Description |
---|
tmplname | name | | Name of the language this template is for | tmpltrusted | boolean | | True if language is considered trusted | tmplhandler | text | | Name of call handler function | tmplvalidator | text | | Name of validator function, or NULL if none | tmpllibrary | text | | Path of shared library that implements language | tmplacl | aclitem[] | | Access privileges for template (not yet used) |
There are not currently any commands that manipulate procedural language
templates; to change the built-in information, a superuser must modify
the table using ordinary INSERT, DELETE, or UPDATE commands. It is
likely that a future release of EnterpriseDB
will offer commands to change the entries in a cleaner fashion.
When implemented, the tmplacl field will provide
access control for the template itself (i.e., the right to create a
language using it), not for the languages created from the template.
pg_proc The catalog pg_proc stores information about functions (or procedures).
The description of CREATE FUNCTION contains more information about the meaning of
some columns.
The table contains data for aggregate functions as well as plain functions.
If proisagg is true, there should be a matching
row in pg_aggregate.
Table 30. pg_proc Columns Name | Type | References | Description |
---|
proname | name | | Name of the function | pronamespace | oid | pg_namespace.oid | The OID of the namespace that contains this function
| proowner | oid | pg_authid.oid | Owner of the function | prolang | oid | pg_language.oid | Implementation language or call interface of this function | proisagg | bool | | Function is an aggregate function | prosecdef | bool | | Function is a security definer (i.e., a "setuid"
function) | proisstrict | bool | | Function returns null if any call argument is null. In that
case the function won't actually be called at all. Functions
that are not "strict" must be prepared to handle
null inputs.
| proretset | bool | | Function returns a set (i.e., multiple values of the specified
data type) | provolatile | char | | provolatile tells whether the function's
result depends only on its input arguments, or is affected by outside
factors.
It is i for "immutable" functions,
which always deliver the same result for the same inputs.
It is s for "stable" functions,
whose results (for fixed inputs) do not change within a scan.
It is v for "volatile" functions,
whose results may change at any time. (Use v also
for functions with side-effects, so that calls to them cannot get
optimized away.)
| pronargs | int2 | | Number of arguments | prorettype | oid | pg_type.oid | Data type of the return value | proargtypes | oidvector | pg_type.oid | An array with the data types of the function arguments. This includes
only input arguments (including INOUT arguments), and thus represents
the call signature of the function.
| proallargtypes | oid[] | pg_type.oid | An array with the data types of the function arguments. This includes
all arguments (including OUT and INOUT arguments); however, if all the
arguments are IN arguments, this field will be null.
Note that subscripting is 1-based, whereas for historical reasons
proargtypes is subscripted from 0.
| proargmodes | char[] | | An array with the modes of the function arguments, encoded as
i for IN arguments,
o for OUT arguments,
b for INOUT arguments.
If all the arguments are IN arguments, this field will be null.
Note that subscripts correspond to positions of
proallargtypes not proargtypes.
| proargnames | text[] | | An array with the names of the function arguments.
Arguments without a name are set to empty strings in the array.
If none of the arguments have a name, this field will be null.
Note that subscripts correspond to positions of
proallargtypes not proargtypes.
| prosrc | text | | This tells the function handler how to invoke the function. It
might be the actual source code of the function for interpreted
languages, a link symbol, a file name, or just about anything
else, depending on the implementation language/call convention.
| probin | bytea | | Additional information about how to invoke the function.
Again, the interpretation is language-specific.
| proacl | aclitem[] | | Access privileges; see
GRANT and
REVOKE
for details.
| proisfunc | boolean | | A boolean value indicating if current relation is a stored
procedure or function | prosig | text | | The signature for the stored procedure or function. This entry
is only populated for SPL stored procedures and
functions.
|
prosrc contains the function's C-language
name (link symbol) for compiled functions, both built-in and
dynamically loaded. For all other language types,
prosrc contains the function's source
text. probin is unused except for
dynamically-loaded C functions, for which it gives the name of the
shared library file containing the function.
pg_rewrite The catalog pg_rewrite stores rewrite rules for tables and views.
Table 31. pg_rewrite Columns Name | Type | References | Description |
---|
rulename | name | | Rule name | ev_class | oid | pg_class.oid | The table this rule is for | ev_attr | int2 | | The column this rule is for (currently, always zero to
indicate the whole table) | ev_type | char | | Event type that the rule is for: 1 = SELECT, 2 =
UPDATE, 3 = INSERT, 4 =
DELETE
| is_instead | bool | | True if the rule is an INSTEAD rule | ev_qual | text | | Expression tree (in the form of a
nodeToString() representation) for the
rule's qualifying condition
| ev_action | text | | Query tree (in the form of a
nodeToString() representation) for the
rule's action
|
Note: pg_class.relhasrules
must be true if a table has any rules in this catalog.
pg_shadow The catalog pg_shadow contains information about
database users. The name stems from the fact that this table
should not be readable by the public since it contains passwords.
pg_user
is a publicly readable view on
pg_shadow that blanks out the password field.
Chapter 31 contains detailed information about user and
privilege management.
Because user identities are cluster-wide,
pg_shadow
is shared across all databases of a cluster: there is only one
copy of pg_shadow per cluster, not
one per database.
Table 32. pg_shadow Columns Name | Type | References | Description |
---|
usename | name | | User name | usesysid | int4 | | User id (arbitrary number used to reference this user) | usecreatedb | bool | | User may create databases | usesuper | bool | | User is a superuser | usecatupd | bool | | User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
| passwd | text | | Password | valuntil | abstime | | Account expiry time (only used for password authentication) | useconfig | text[] | | Session defaults for run-time configuration variables |
pg_shdepend The catalog pg_shdepend records the
dependency relationships between database objects and shared objects,
such as roles. This information allows
EnterpriseDB to ensure that those objects are
unreferenced before attempting to delete them.
See also pg_depend,
which performs a similar function for dependencies involving objects
within a single database.
Unlike most system catalogs, pg_shdepend
is shared across all databases of a cluster: there is only one
copy of pg_shdepend per cluster, not
one per database.
Table 33. pg_shdepend Columns Name | Type | References | Description |
---|
dbid | oid | pg_database.oid | The OID of the database the dependent object is in,
or zero for a shared object | classid | oid | pg_class.oid | The OID of the system catalog the dependent object is in | objid | oid | any OID column | The OID of the specific dependent object | refclassid | oid | pg_class.oid | The OID of the system catalog the referenced object is in
(must be a shared catalog) | refobjid | oid | any OID column | The OID of the specific referenced object | deptype | char | | A code defining the specific semantics of this dependency relationship; see text.
|
In all cases, a pg_shdepend entry indicates that
the referenced object may not be dropped without also dropping the dependent
object. However, there are several subflavors identified by
deptype:
- SHARED_DEPENDENCY_OWNER (o)
The referenced object (which must be a role) is the owner of the
dependent object.
- SHARED_DEPENDENCY_ACL (a)
The referenced object (which must be a role) is mentioned in the
ACL (access control list, i.e., privileges list) of the
dependent object. (A SHARED_DEPENDENCY_ACL entry is
not made for the owner of the object, since the owner will have
a SHARED_DEPENDENCY_OWNER entry anyway.)
- SHARED_DEPENDENCY_PIN (p)
There is no dependent object; this type of entry is a signal
that the system itself depends on the referenced object, and so
that object must never be deleted. Entries of this type are
created only by initdb. The columns for the
dependent object contain zeroes.
Other dependency flavors may be needed in future. Note in particular
that the current definition only supports roles as referenced objects.
pg_statistic The catalog pg_statistic stores statistical data
about the contents of the database. Entries are created by
ANALYZE and subsequently used by the query planner.
There is one entry for each table column that has been analyzed.
Note that all the statistical data is inherently approximate,
even assuming that it is up-to-date.
pg_statistic also stores statistical data about
the values of index expressions. These are described as if they were
actual data columns; in particular, starelid
references the index. No entry is made for an ordinary non-expression
index column, however, since it would be redundant with the entry
for the underlying table column.
Since different kinds of statistics may be appropriate for different
kinds of data, pg_statistic is designed not
to assume very much about what sort of statistics it stores. Only
extremely general statistics (such as nullness) are given dedicated
columns in pg_statistic. Everything else
is stored in "slots", which are groups of associated columns
whose content is identified by a code number in one of the slot's columns.
For more information see
src/include/catalog/pg_statistic.h.
pg_statistic should not be readable by the
public, since even statistical information about a table's contents
may be considered sensitive. (Example: minimum and maximum values
of a salary column might be quite interesting.)
pg_stats
is a publicly readable view on
pg_statistic that only exposes information
about those tables that are readable by the current user.
Table 34. pg_statistic Columns Name | Type | References | Description |
---|
starelid | oid | pg_class.oid | The table or index that the described column belongs to | staattnum | int2 | pg_attribute.attnum | The number of the described column | stanullfrac | float4 | | The fraction of the column's entries that are null | stawidth | int4 | | The average stored width, in bytes, of nonnull entries | stadistinct | float4 | | The number of distinct nonnull data values in the column.
A value greater than zero is the actual number of distinct values.
A value less than zero is the negative of a fraction of the number
of rows in the table (for example, a column in which values appear about
twice on the average could be represented by stadistinct = -0.5).
A zero value means the number of distinct values is unknown.
| stakindN | int2 | | A code number indicating the kind of statistics stored in the
Nth "slot" of the
pg_statistic row.
| staopN | oid | pg_operator.oid | An operator used to derive the statistics stored in the
Nth "slot". For example, a
histogram slot would show the < operator
that defines the sort order of the data.
| stanumbersN | float4[] | | Numerical statistics of the appropriate kind for the
Nth "slot", or null if the slot
kind does not involve numerical values.
| stavaluesN | anyarray | | Column data values of the appropriate kind for the
Nth "slot", or null if the slot
kind does not store any data values. Each array's element
values are actually of the specific column's data type, so there
is no way to define these columns' type more specifically than
anyarray.
|
pg_synonym The catalog pg_synonym stores the public synonyms that have been defined for objects in the database.
Table 35. pg_synonym Columns Name | Type | References | Description |
---|
synname | name | | Synonym name | synowner | int4 | pg_shadow.usesysid | Owner of the synonym | synobjschema | name | | Namespace that contains synobjname | synobjname | name | | Name of the relation or other database object for which this synonym is defined | synacl | aclitem[] | | Access privileges
|
pg_tablespace The catalog pg_tablespace stores information
about the available tablespaces. Tables can be placed in particular
tablespaces to aid administration of disk layout.
Unlike most system catalogs, pg_tablespace
is shared across all databases of a cluster: there is only one
copy of pg_tablespace per cluster, not
one per database.
Table 36. pg_tablespace Columns Name | Type | References | Description |
---|
spcname | name | | Tablespace name | spcowner | int4 | pg_shadow.usesysid | Owner of the tablespace, usually the user who created it | spclocation | text | | Location (directory path) of the tablespace | spcacl | aclitem[] | | Access privileges |
pg_trigger The catalog pg_trigger stores triggers on tables. See under
CREATE TRIGGER for more information.
Table 37. pg_trigger Columns Name | Type | References | Description |
---|
tgrelid | oid | pg_class.oid | The table this trigger is on | tgname | name | | Trigger name (must be unique among triggers of same table) | tgfoid | oid | pg_proc.oid | The function to be called | tgtype | int2 | | Bit mask identifying trigger conditions | tgenabled | bool | | True if trigger is enabled (not presently checked everywhere
it should be, so disabling a trigger by setting this false does not
work reliably) | tgisconstraint | bool | | True if trigger implements a referential integrity constraint | tgconstrname | name | | Referential integrity constraint name | tgconstrrelid | oid | pg_class.oid | The table referenced by an referential integrity constraint | tgdeferrable | bool | | True if deferrable | tginitdeferred | bool | | True if initially deferred | tgnargs | int2 | | Number of argument strings passed to trigger function | tgattr | int2vector | | Currently unused | tgargs | bytea | | Argument strings to pass to trigger, each null-terminated |
Note: pg_class.reltriggers needs to match up with the
entries in this table.
pg_type The catalog pg_type stores information about data types. Base types
(scalar types) are created with CREATE TYPE.
A composite type is automatically created for each table in the database, to
represent the row structure of the table. It is also possible to create
composite types with CREATE TYPE AS and
domains with CREATE DOMAIN.
Table 38. pg_type Columns Name | Type | References | Description |
---|
typname | name | | Data type name | typnamespace | oid | pg_namespace.oid | The OID of the namespace that contains this type
| typowner | int4 | pg_shadow.usesysid | Owner of the type | typlen | int2 | | For a fixed-size type, typlen is the number
of bytes in the internal representation of the type. But for a
variable-length type, typlen is negative.
-1 indicates a "varlena" type (one that has a length word),
-2 indicates a null-terminated C string.
| typbyval | bool | | typbyval determines whether internal
routines pass a value of this type by value or by reference.
typbyval had better be false if
typlen is not 1, 2, or 4 (or 8 on machines
where Datum is 8 bytes).
Variable-length types are always passed by reference. Note that
typbyval can be false even if the
length would allow pass-by-value; this is currently true for
type float4, for example.
| typtype | char | | typtype is b for
a base type, c for a composite type (e.g., a
table's row type), d for a domain, or
p for a pseudo-type. See also
typrelid and
typbasetype.
| typisdefined | bool | | True if the type is defined, false if this is a placeholder
entry for a not-yet-defined type. When
typisdefined is false, nothing
except the type name, namespace, and OID can be relied on.
| typdelim | char | | Character that separates two values of this type when parsing
array input. Note that the delimiter is associated with the array
element data type, not the array data type. | typrelid | oid | pg_class.oid | If this is a composite type (see
typtype), then this column points to
the pg_class entry that defines the
corresponding table. (For a free-standing composite type, the
pg_class entry doesn't really represent
a table, but it is needed anyway for the type's
pg_attribute entries to link to.)
Zero for non-composite types.
| typelem | oid | pg_type.oid | If typelem is not 0 then it
identifies another row in pg_type.
The current type can then be subscripted like an array yielding
values of type typelem. A
"true" array type is variable length
(typlen = -1),
but some fixed-length (typlen > 0) types
also have nonzero typelem, for example
name and oidvector.
If a fixed-length type has a typelem then
its internal representation must be some number of values of the
typelem data type with no other data.
Variable-length array types have a header defined by the array
subroutines.
| typinput | regproc | pg_proc.oid | Input conversion function (text format) | typoutput | regproc | pg_proc.oid | Output conversion function (text format) | typreceive | regproc | pg_proc.oid | Input conversion function (binary format), or 0 if none | typsend | regproc | pg_proc.oid | Output conversion function (binary format), or 0 if none | typanalyze | regproc | pg_proc.oid | Custom ANALYZE function, or 0 to use the standard function | typalign | char | |
typalign is the alignment required
when storing a value of this type. It applies to storage on
disk as well as most representations of the value inside
EnterpriseDB.
When multiple values are stored consecutively, such
as in the representation of a complete row on disk, padding is
inserted before a datum of this type so that it begins on the
specified boundary. The alignment reference is the beginning
of the first datum in the sequence.
Possible values are:
c = char alignment, i.e., no alignment needed. s = short alignment (2 bytes on most machines). i = int alignment (4 bytes on most machines). d = double alignment (8 bytes on many machines, but by no means all).
Note: For types used in system tables, it is critical that the size
and alignment defined in pg_type
agree with the way that the compiler will lay out the column in
a structure representing a table row.
| typstorage | char | | typstorage tells for varlena
types (those with typlen = -1) if
the type is prepared for toasting and what the default strategy
for attributes of this type should be.
Possible values are
p: Value must always be stored plain. e: Value can be stored in a "secondary"
relation (if relation has one, see
pg_class.reltoastrelid).
m: Value can be stored compressed inline. x: Value can be stored compressed inline or stored in "secondary" storage.
Note that m columns can also be moved out to secondary
storage, but only as a last resort (e and x columns are
moved first).
| typnotnull | bool | | typnotnull represents a not-null
constraint on a type. Used for domains only.
| typbasetype | oid | pg_type.oid | If this is a domain (see typtype),
then typbasetype identifies
the type that this one is based on. Zero if not a domain.
| typtypmod | int4 | | Domains use typtypmod to record the typmod
to be applied to their base type (-1 if base type does not use a
typmod). -1 if this type is not a domain.
| typndims | int4 | | typndims is the number of array dimensions
for a domain that is an array (that is, typbasetype is an array type;
the domain's typelem will match the base type's typelem).
Zero for types other than array domains.
| typdefaultbin | text | | If typdefaultbin is not null, it is the nodeToString()
representation of a default expression for the type. This is
only used for domains.
| typdefault | text | | typdefault is null if the type has no associated
default value. If typdefaultbin is not null,
typdefault must contain a human-readable version of the
default expression represented by typdefaultbin. If
typdefaultbin is null and typdefault is
not, then typdefault is the external representation of
the type's default value, which may be fed to the type's input
converter to produce a constant.
|
System Views In addition to the system catalogs, EnterpriseDB
provides a number of built-in views. The system views provide convenient
access to some commonly used queries on the system catalogs. Some of these
views provide access to internal server state, as well.
Table 39 lists the system views described here.
More detailed documentation of each view follows below.
There are some additional views that provide access to the results of
the statistics collector; they are described in Table 37-1.
The information schema provides
an alternative set of views which overlap the functionality of the system
views. Since the information schema is SQL-standard whereas the views
described here are EnterpriseDB-specific,
it's usually better to use the information schema if it provides all
the information you need.
Except where noted, all the views described here are read-only.
pg_indexes The view pg_indexes provides access to
useful information about each index in the database.
Table 40. pg_indexes Columns Name | Type | References | Description |
---|
schemaname | name | pg_namespace.nspname | name of schema containing table and index | tablename | name | pg_class.relname | name of table the index is for | indexname | name | pg_class.relname | name of index | tablespace | name | pg_tablespace.spcname | name of tablespace containing index (NULL if default for database) | indexdef | text | | index definition (a reconstructed creation command) |
pg_locks The view pg_locks provides access to
information about the locks held by open transactions within the
database server. See MVCC for more discussion
of locking.
pg_locks contains one row per active lockable
object, requested lock mode, and relevant transaction. Thus, the same
lockable object may
appear many times, if multiple transactions are holding or waiting
for locks on it. However, an object that currently has no locks on it
will not appear at all. A lockable object is either a relation (e.g., a
table) or a transaction ID.
Note that this view includes only table-level
locks, not row-level ones. If a transaction is waiting for a
row-level lock, it will appear in the view as waiting for the
transaction ID of the current holder of that row lock.
Table 41. pg_locks Columns Name | Type | References | Description |
---|
relation | oid | pg_class.oid | OID of the locked relation, or NULL if the lockable object
is a transaction ID
| database | oid | pg_database.oid | OID of the database in which the locked relation exists, or
zero if the locked relation is a globally-shared table, or
NULL if the lockable object is a transaction ID
| transaction | xid | | ID of a transaction, or NULL if the lockable object is a relation
| pid | integer | | process ID of a server process holding or awaiting this
lock | mode | text | | name of the lock mode held or desired by this process (see Section 11.3.1) | granted | boolean | | true if lock is held, false if lock is awaited |
granted is true in a row representing a lock
held by the indicated session. False indicates that this session is
currently waiting to acquire this lock, which implies that some other
session is holding a conflicting lock mode on the same lockable object.
The waiting session will sleep until the other lock is released (or a
deadlock situation is detected). A single session can be waiting to acquire
at most one lock at a time.
Every transaction holds an exclusive lock on its transaction ID for its
entire duration. If one transaction finds it necessary to wait specifically
for another transaction, it does so by attempting to acquire share lock on
the other transaction ID. That will succeed only when the other transaction
terminates and releases its locks.
When the pg_locks view is accessed, the
internal lock manager data structures are momentarily locked, and
a copy is made for the view to display. This ensures that the
view produces a consistent set of results, while not blocking
normal lock manager operations longer than necessary. Nonetheless
there could be some impact on database performance if this view is
read often.
pg_locks provides a global view of all locks
in the database cluster, not only those relevant to the current database.
Although its relation column can be joined
against pg_class.oid to identify locked
relations, this will only work correctly for relations in the current
database (those for which the database column
is either the current database's OID or zero).
If you have enabled the statistics collector, the
pid column can be joined to the
procpid column of the
pg_stat_activity view to get more
information on the session holding or waiting to hold the lock.
pg_prepared_xacts The view pg_prepared_xacts displays
information about transactions that are currently prepared for two-phase
commit (see PREPARE TRANSACTION for details).
pg_prepared_xacts contains one row per prepared
transaction. An entry is removed when the transaction is committed or
rolled back.
Table 42. pg_prepared_xacts Columns Name | Type | References | Description |
---|
transaction | xid | | Numeric transaction identifier of the prepared transaction
| gid | text | | Global transaction identifier that was assigned to the transaction
| prepared | timestamp with time zone | | Time at which the transaction was prepared for commit
| owner | name | pg_authid.rolname | Name of the user that executed the transaction
| database | name | pg_database.datname | Name of the database in which the transaction was executed
|
When the pg_prepared_xacts view is accessed, the
internal transaction manager data structures are momentarily locked, and
a copy is made for the view to display. This ensures that the
view produces a consistent set of results, while not blocking
normal operations longer than necessary. Nonetheless
there could be some impact on database performance if this view is
read often.
pg_roles The view pg_roles provides access to
information about database roles. This is simply a publicly
readable view of
pg_authid
that blanks out the password field.
This view explicitly exposes the OID column of the underlying table,
since that is needed to do joins to other catalogs.
Table 43. pg_roles Columns Name | Type | References | Description |
---|
rolname | name | | Role name | rolsuper | bool | | Role has superuser privileges | rolinherit | bool | | Role automatically inherits privileges of roles it is a
member of | rolcreaterole | bool | | Role may create more roles | rolcreatedb | bool | | Role may create databases | rolcatupdate | bool | | Role may update system catalogs directly. (Even a superuser may not do
this unless this column is true.)
| rolcanlogin | bool | | Role may log in, that is, this role can be given as the initial
session authorization identifier.
| rolconnlimit | int4 | | For roles that can log in, this sets maximum number of concurrent
connections this role can make. -1 means no limit.
| rolpassword | text | | Not the password (always reads as ********) | rolvaliduntil | timestamptz | | Password expiry time (only used for password authentication);
NULL if no expiration | rolconfig | text[] | | Session defaults for run-time configuration variables | oid | oid | pg_authid.oid | ID of role |
pg_rules The view pg_rules provides access to
useful information about query rewrite rules.
Table 44. pg_rules Columns Name | Type | References | Description |
---|
schemaname | name | pg_namespace.nspname | name of schema containing table | tablename | name | pg_class.relname | name of table the rule is for | rulename | name | pg_rewrite.rulename | name of rule | definition | text | | rule definition (a reconstructed creation command) |
The pg_rules view excludes the ON SELECT rules of
views; those can be seen in pg_views.
pg_settings The view pg_settings provides access to
run-time parameters of the server. It is essentially an alternative
interface to the SHOW and SET commands.
It also provides access to some facts about each parameter that are
not directly available from SHOW, such as minimum and
maximum values.
Table 45. pg_settings Columns Name | Type | References | Description |
---|
name | text | | run-time configuration parameter name | setting | text | | current value of the parameter | category | text | | logical group of the parameter | short_desc | text | | a brief description of the parameter | extra_desc | text | | additional, more detailed, information about the parameter | context | text | | context required to set the parameter's value | vartype | text | | parameter type (bool, integer,
real, or string)
| source | text | | source of the current parameter value | min_val | text | | minimum allowed value of the parameter (NULL for nonnumeric
values) | max_val | text | | maximum allowed value of the parameter (NULL for nonnumeric
values) |
The pg_settings view cannot be inserted into or
deleted from, but it can be updated. An UPDATE applied
to a row of pg_settings is equivalent to executing
the SET command on that named
parameter. The change only affects the value used by the current
session. If an UPDATE is issued within a transaction
that is later aborted, the effects of the UPDATE command
disappear when the transaction is rolled back. Once the surrounding
transaction is committed, the effects will persist until the end of the
session, unless overridden by another UPDATE or
SET.
pg_stats The view pg_stats provides access to
the information stored in the pg_statistic
catalog. This view allows access only to rows of
pg_statistic that correspond to tables the
user has permission to read, and therefore it is safe to allow public
read access to this view.
pg_stats is also designed to present the
information in a more readable format than the underlying catalog
- at the cost that its schema must be extended whenever new slot types
are defined for pg_statistic.
Table 46. pg_stats Columns Name | Type | References | Description |
---|
schemaname | name | pg_namespace.nspname | name of schema containing table | tablename | name | pg_class.relname | name of table | attname | name | pg_attribute.attname | name of the column described by this row | null_frac | real | | fraction of column entries that are null | avg_width | integer | | average width in bytes of column's entries | n_distinct | real | | If greater than zero, the estimated number of distinct values
in the column. If less than zero, the negative of the number of
distinct values divided by the number of rows. (The negated form
is used when ANALYZE believes that the number of distinct
values
is likely to increase as the table grows; the positive form is used
when the column seems to have a fixed number of possible values.)
For example, -1 indicates a unique column in which the number of
distinct values is the same as the number of rows.
| most_common_vals | anyarray | | A list of the most common values in the column. (NULL if
no values seem to be more common than any others.) | most_common_freqs | real[] | | A list of the frequencies of the most common values,
i.e., number of occurrences of each divided by total number of rows.
(NULL when most_common_vals is.)
| histogram_bounds | anyarray | | A list of values that divide the column's values into
groups of approximately equal population. The values in
most_common_vals, if present, are omitted from this
histogram calculation. (This column is NULL if the column data type
does not have a < operator or if the
most_common_vals list accounts for the entire
population.)
| correlation | real | | Statistical correlation between physical row ordering and
logical ordering of the column values. This ranges from -1 to +1.
When the value is near -1 or +1, an index scan on the column will
be estimated to be cheaper than when it is near zero, due to reduction
of random access to the disk. (This column is NULL if the column data
type does not have a < operator.)
|
The maximum number of entries in the most_common_vals
and histogram_bounds arrays can be set on a
column-by-column basis using the ALTER TABLE SET STATISTICS
command, or globally by setting the
default_statistics_target runtime parameter.
pg_tables The view pg_tables provides access to
useful information about each table in the database.
Table 47. pg_tables Columns Name | Type | References | Description |
---|
schemaname | name | pg_namespace.nspname | name of schema containing table | tablename | name | pg_class.relname | name of table | tableowner | name | pg_shadow.usename | name of table's owner | tablespace | name | pg_tablespace.spcname | name of tablespace containing table (NULL if default for database) | hasindexes | boolean | pg_class.relhasindex | true if table has (or recently had) any indexes | hasrules | boolean | pg_class.relhasrules | true if table has rules | hastriggers | boolean | pg_class.reltriggers | true if table has triggers |
pg_user The view pg_user provides access to
information about database users. This is simply a publicly
readable view of
pg_shadow
that blanks out the password field.
Table 48. pg_user Columns Name | Type | References | Description |
---|
usename | name | | User name | usesysid | int4 | | User id (arbitrary number used to reference this user) | usecreatedb | bool | | User may create databases | usesuper | bool | | User is a superuser | usecatupd | bool | | User may update system catalogs. (Even a superuser may not do
this unless this column is true.)
| passwd | text | | Not the password (always reads as ********) | valuntil | abstime | | Account expiry time (only used for password authentication) | useconfig | text[] | | Session defaults for run-time configuration variables |
pg_views The view pg_views provides access to
useful information about each view in the database.
Table 49. pg_views Columns Name | Type | References | Description |
---|
schemaname | name | pg_namespace.nspname | name of schema containing view | viewname | name | pg_class.relname | name of view | viewowner | name | pg_shadow.usename | name of view's owner | definition | text | | view definition (a reconstructed SELECT query) |
| |
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