postgres_fdw: Allow partitions specified in LIMIT TO to be imported.

Commit f49bcd4ef3 disallowed postgres_fdw to import table partitions.
Because all data can be accessed through the partitioned table which
is the root of the partitioning hierarchy, importing only partitioned
table should allow access to all the data without creating extra objects.
This is a reasonable default when importing a whole schema. But there
may be the case where users want to explicitly import one of
a partitioned tables' partitions.

For that use case, this commit allows postgres_fdw to import tables or
foreign tables which are partitions of some other table only when they
are explicitly specified in LIMIT TO clause.  It doesn't change
the behavior that any partitions not specified in LIMIT TO are
automatically excluded in IMPORT FOREIGN SCHEMA command.

Author: Matthias van de Meent
Reviewed-by: Bernd Helmle, Amit Langote, Michael Paquier, Fujii Masao
Discussion: https://postgr.es/m/CAEze2Whwg4i=mzApMe+PXxCEfgoZmHGqdqQFW7J4bmj_5p6t1A@mail.gmail.com

1 files changed, 7 insertions, 4 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 16c2979f2d0..b6442070a35 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -5095,9 +5095,11 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 		 * should save a few cycles to not process excluded tables in the
 		 * first place.)
 		 *
-		 * Ignore table data for partitions and only include the definitions
-		 * of the root partitioned tables to allow access to the complete
-		 * remote data set locally in the schema imported.
+		 * Import table data for partitions only when they are explicitly
+		 * specified in LIMIT TO clause. Otherwise ignore them and only
+		 * include the definitions of the root partitioned tables to allow
+		 * access to the complete remote data set locally in the schema
+		 * imported.
 		 *
 		 * Note: because we run the connection with search_path restricted to
 		 * pg_catalog, the format_type() and pg_get_expr() outputs will always
@@ -5153,7 +5155,8 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
 		deparseStringLiteral(&buf, stmt->remote_schema);
 
 		/* Partitions are supported since Postgres 10 */
-		if (PQserverVersion(conn) >= 100000)
+		if (PQserverVersion(conn) >= 100000 &&
+			stmt->list_type != FDW_IMPORT_SCHEMA_LIMIT_TO)
 			appendStringInfoString(&buf, " AND NOT c.relispartition ");
 
 		/* Apply restrictions for LIMIT TO and EXCEPT */