PostgreSQL 7.1.3 Documentation
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# 3.16. pg_type

Table 3-16. pg_type Columns

Name | Type | References | Description
--- | --- | --- | ---
typname | `name` |  | Data type name
typowner | `int4` | pg_shadow.usesysid | Owner (creator) of the type
typlen | `int2` |  | Length of the storage representation of the type, -1 if variable length
typprtlen | `int2` |  | unused

typbyval

`bool`

`typbyval` determines whether internal routines pass a value of this type by value or by reference. Only `char`, `short`, and `int` equivalent items can be passed by value, so if the type is not 1, 2, or 4 bytes long, Postgres does not have the option of passing by value and so `typbyval` had better be false. 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 basic type and `c` for a catalog type (i.e., a table). If `typtype` is `c`, `typrelid` is the OID of the type's entry in `pg_class`.
typisdefined | `bool` |  | ???
typdelim | `char` |  | Character that separates two values of this type when parsing array input
typrelid | `oid` | pg_class.oid | If this is a catalog type (see `typtype`), then this field points to the `pg_class` entry that defines the corresponding table. A table could theoretically be used as a composite data type, but this is not fully functional.

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 non-zero `typelem` does not guarantee this type to be a "real" array type; some ordinary fixed-length types can also be subscripted (e.g., `oidvector`). Variable-length types can not be turned into pseudo-arrays like that. Hence, the way to determine whether a type is a "true" array type is typelem != 0 and typlen < 0.

typinput | `regproc` |  | Input function
typoutput | `regproc` |  | Output function
typreceive | `regproc` |  | unused
typsend | `regproc` |  | unused

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 Postgres. 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 field in a struct representing a table row.

typstorage

`char`

`typstorage` tells for variable-length 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 in "secondary".

Note that 'm' fields can also be moved out to secondary storage, but only as a last resort ('e' and 'x' fields are moved first).

typdefault | `text` |  | ???

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