postgres_fdw: be more wary about shippability of reg* constants.

Don't consider a constant of regconfig or other reg* types to be
shippable unless it refers to a built-in object, or an object in
an extension that's been marked shippable.  Without this
restriction, we're too likely to send a constant that will fail
to parse on the remote server.

For the regconfig type only, consider OIDs up to 16383 to be
"built in", rather than the normal cutoff of 9999.  Otherwise
the initdb-created text search configurations will be considered
unshippable, which is unlikely to make anyone happy.

It's possible that this new restriction will de-optimize queries
that were working satisfactorily before.  Users can restore any
lost performance by making sure that objects that can be expected
to exist on the remote side are in shippable extensions.  However,
that's not a change that people are likely to be happy about having
to make after a minor-release update.  Between that consideration
and the lack of field complaints, let's just change this in HEAD.

Noted while fixing bug #17483, although this is not precisely
the problem that that report complained about.

Discussion: https://postgr.es/m/1423433.1652722406@sss.pgh.pa.us

1 files changed, 11 insertions, 1 deletions

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index a4f988fdb82..b7817c5a415 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -442,7 +442,8 @@ SELECT * FROM ft1 WHERE CASE c3 WHEN c6 THEN true ELSE c3 < 'bar' END;
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT * FROM ft1 WHERE CASE c3 COLLATE "C" WHEN c6 THEN true ELSE c3 < 'bar' END;
 
--- check schema-qualification of regconfig constant
+-- a regconfig constant referring to this text search configuration
+-- is initially unshippable
 CREATE TEXT SEARCH CONFIGURATION public.custom_search
   (COPY = pg_catalog.english);
 EXPLAIN (VERBOSE, COSTS OFF)
@@ -450,6 +451,15 @@ SELECT c1, to_tsvector('custom_search'::regconfig, c3) FROM ft1
 WHERE c1 = 642 AND length(to_tsvector('custom_search'::regconfig, c3)) > 0;
 SELECT c1, to_tsvector('custom_search'::regconfig, c3) FROM ft1
 WHERE c1 = 642 AND length(to_tsvector('custom_search'::regconfig, c3)) > 0;
+-- but if it's in a shippable extension, it can be shipped
+ALTER EXTENSION postgres_fdw ADD TEXT SEARCH CONFIGURATION public.custom_search;
+-- however, that doesn't flush the shippability cache, so do a quick reconnect
+\c -
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT c1, to_tsvector('custom_search'::regconfig, c3) FROM ft1
+WHERE c1 = 642 AND length(to_tsvector('custom_search'::regconfig, c3)) > 0;
+SELECT c1, to_tsvector('custom_search'::regconfig, c3) FROM ft1
+WHERE c1 = 642 AND length(to_tsvector('custom_search'::regconfig, c3)) > 0;
 
 -- ===================================================================
 -- JOIN queries