diff options
Diffstat (limited to 'doc/src/sgml/ref')
| -rw-r--r-- | doc/src/sgml/ref/create_type.sgml | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/doc/src/sgml/ref/create_type.sgml b/doc/src/sgml/ref/create_type.sgml index e5d7992bbf5..f9e1297d0b0 100644 --- a/doc/src/sgml/ref/create_type.sgml +++ b/doc/src/sgml/ref/create_type.sgml @@ -329,15 +329,17 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> to <literal>VARIABLE</literal>. (Internally, this is represented by setting <literal>typlen</> to -1.) The internal representation of all variable-length types must start with a 4-byte integer giving the total - length of this value of the type. + length of this value of the type. (Note that the length field is often + encoded, as described in <xref linkend="storage-toast">; it's unwise + to access it directly.) </para> <para> The optional flag <literal>PASSEDBYVALUE</literal> indicates that values of this data type are passed by value, rather than by - reference. You cannot pass by value types whose internal - representation is larger than the size of the <type>Datum</> type - (4 bytes on most machines, 8 bytes on a few). + reference. Types passed by value must be fixed-length, and their internal + representation cannot be larger than the size of the <type>Datum</> type + (4 bytes on some machines, 8 bytes on others). </para> <para> @@ -368,6 +370,17 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> </para> <para> + All <replaceable class="parameter">storage</replaceable> values other + than <literal>plain</literal> imply that the functions of the data type + can handle values that have been <firstterm>toasted</>, as described + in <xref linkend="storage-toast"> and <xref linkend="xtypes-toast">. + The specific other value given merely determines the default TOAST + storage strategy for columns of a toastable data type; users can pick + other strategies for individual columns using <literal>ALTER TABLE + SET STORAGE</>. + </para> + + <para> The <replaceable class="parameter">like_type</replaceable> parameter provides an alternative method for specifying the basic representation properties of a data type: copy them from some existing type. The values of @@ -465,8 +478,8 @@ CREATE TYPE <replaceable class="parameter">name</replaceable> identical things, and you want to allow these things to be accessed directly by subscripting, in addition to whatever operations you plan to provide for the type as a whole. For example, type <type>point</> - is represented as just two floating-point numbers, each can be accessed using - <literal>point[0]</> and <literal>point[1]</>. + is represented as just two floating-point numbers, which can be accessed + using <literal>point[0]</> and <literal>point[1]</>. Note that this facility only works for fixed-length types whose internal form is exactly a sequence of identical fixed-length fields. A subscriptable |