diff options
Diffstat (limited to 'doc/src/sgml/gist.sgml')
| -rw-r--r-- | doc/src/sgml/gist.sgml | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/doc/src/sgml/gist.sgml b/doc/src/sgml/gist.sgml index e7d1ff9d83f..1291f8dd0c8 100644 --- a/doc/src/sgml/gist.sgml +++ b/doc/src/sgml/gist.sgml @@ -105,6 +105,7 @@ <literal>~=</> </entry> <entry> + <literal><-></> </entry> </row> <row> @@ -163,6 +164,7 @@ <literal>~=</> </entry> <entry> + <literal><-></> </entry> </row> <row> @@ -207,6 +209,12 @@ </table> <para> + Currently, ordering by the distance operator <literal><-></> + is supported only with <literal>point</> by the operator classes + of the geometric types. + </para> + + <para> For historical reasons, the <literal>inet_ops</> operator class is not the default class for types <type>inet</> and <type>cidr</>. To use it, mention the class name in <command>CREATE INDEX</>, @@ -780,6 +788,7 @@ my_distance(PG_FUNCTION_ARGS) data_type *query = PG_GETARG_DATA_TYPE_P(1); StrategyNumber strategy = (StrategyNumber) PG_GETARG_UINT16(2); /* Oid subtype = PG_GETARG_OID(3); */ + /* bool *recheck = (bool *) PG_GETARG_POINTER(4); */ data_type *key = DatumGetDataType(entry->key); double retval; @@ -792,14 +801,24 @@ my_distance(PG_FUNCTION_ARGS) </programlisting> The arguments to the <function>distance</> function are identical to - the arguments of the <function>consistent</> function, except that no - recheck flag is used. The distance to a leaf index entry must always - be determined exactly, since there is no way to re-order the tuples - once they are returned. Some approximation is allowed when determining - the distance to an internal tree node, so long as the result is never - greater than any child's actual distance. Thus, for example, distance - to a bounding box is usually sufficient in geometric applications. The - result value can be any finite <type>float8</> value. (Infinity and + the arguments of the <function>consistent</> function. + </para> + + <para> + Some approximation is allowed when determining the distance, as long as + the result is never greater than the entry's actual distance. Thus, for + example, distance to a bounding box is usually sufficient in geometric + applications. For an internal tree node, the distance returned must not + be greater than the distance to any of the child nodes. If the returned + distance is not accurate, the function must set *recheck to false. (This + is not necessary for internal tree nodes; for them, the calculation is + always assumed to be inaccurate). The executor will calculate the + accurate distance after fetching the tuple from the heap, and reorder + the tuples if necessary. + </para> + + <para> + The result value can be any finite <type>float8</> value. (Infinity and minus infinity are used internally to handle cases such as nulls, so it is not recommended that <function>distance</> functions return these values.) |