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Diffstat (limited to 'doc/src/sgml/postgres-fdw.sgml')
| -rw-r--r-- | doc/src/sgml/postgres-fdw.sgml | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/doc/src/sgml/postgres-fdw.sgml b/doc/src/sgml/postgres-fdw.sgml index 61cc2aafc24..4aa798ac2ee 100644 --- a/doc/src/sgml/postgres-fdw.sgml +++ b/doc/src/sgml/postgres-fdw.sgml @@ -319,6 +319,26 @@ </sect2> <sect2> + <title>Cross-Version Compatibility</title> + + <para> + <filename>postgres_fdw</> can be used with remote servers dating back + to <productname>PostgreSQL</> 8.3. Read-only capability is available + back to 8.1. A limitation however is that <filename>postgres_fdw</> + generally assumes that immutable built-in functions and operators are + safe to send to the remote server for execution, if they appear in a + <literal>WHERE</> clause for a foreign table. Thus, a built-in + function that was added since the remote server's release might be sent + to it for execution, resulting in <quote>function does not exist</> or + a similar error. This type of failure can be worked around by + rewriting the query, for example by embedding the foreign table + reference in a sub-<literal>SELECT</> with <literal>OFFSET 0</> as an + optimization fence, and placing the problematic function or operator + outside the sub-<literal>SELECT</>. + </para> + </sect2> + + <sect2> <title>Author</title> <para> Shigeru Hanada <email>shigeru.hanada@gmail.com</email> |