diff options
| author | Tom Lane | 2015-05-25 18:12:51 +0000 |
|---|---|---|
| committer | Tom Lane | 2015-05-25 18:13:02 +0000 |
| commit | e70ec8230a2c0e7363bb7abf4d55dddbdec89fe1 (patch) | |
| tree | 7353130c7603197002f10bb4117565168009a0a7 | |
| parent | cdbdc4382743fcfabb3437ea7c4d103adaa01324 (diff) | |
Explain CHECK constraint handling in postgres_fdw's IMPORT FOREIGN SCHEMA.
The existing documentation could easily be misinterpreted, and it failed to
explain the inconsistent-evaluation hazard that deterred us from supporting
automatic importing of check constraints. Revise it.
Etsuro Fujita, further expanded by me
| -rw-r--r-- | doc/src/sgml/postgres-fdw.sgml | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 1079140de2..14b12e37dc 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -309,8 +309,8 @@ using <xref linkend="sql-importforeignschema">. This command creates foreign table definitions on the local server that match tables or views present on the remote server. If the remote tables to be imported - have columns of user-defined data types, the local server must have types - of the same names. + have columns of user-defined data types, the local server must have + compatible types of the same names. </para> <para> @@ -361,9 +361,16 @@ <para> Note that constraints other than <literal>NOT NULL</> will never be - imported from the remote tables, since <productname>PostgreSQL</> - does not support any other type of constraint on a foreign table. - Checking other types of constraints is always left to the remote server. + imported from the remote tables. Although <productname>PostgreSQL</> + does support <literal>CHECK</> constraints on foreign tables, there is no + provision for importing them automatically, because of the risk that a + constraint expression could evaluate differently on the local and remote + servers. Any such inconsistency in the behavior of a <literal>CHECK</> + constraint could lead to hard-to-detect errors in query optimization. + So if you wish to import <literal>CHECK</> constraints, you must do so + manually, and you should verify the semantics of each one carefully. + For more detail about the treatment of <literal>CHECK</> constraints on + foreign tables, see <xref linkend="sql-createforeigntable">. </para> </sect3> </sect2> |