Allow postgres_fdw to ship extension funcs/operators for remote execution.

The user can whitelist specified extension(s) in the foreign server's
options, whereupon we will treat immutable functions and operators of those
extensions as candidates to be sent for remote execution.

Whitelisting an extension in this way basically promises that the extension
exists on the remote server and behaves compatibly with the local instance.
We have no way to prove that formally, so we have to rely on the user to
get it right.  But this seems like something that people can usually get
right in practice.

We might in future allow functions and operators to be whitelisted
individually, but extension granularity is a very convenient special case,
so it got done first.

The patch as-committed lacks any regression tests, which is unfortunate,
but introducing dependencies on other extensions for testing purposes
would break "make installcheck" scenarios, which is worse.  I have some
ideas about klugy ways around that, but it seems like material for a
separate patch.  For the moment, leave the problem open.

Paul Ramsey, hacked up a bit more by me

1 files changed, 42 insertions, 1 deletions

diff --git a/contrib/postgres_fdw/postgres_fdw.h b/contrib/postgres_fdw/postgres_fdw.h
index 8956cd2cf1c..f243de8d623 100644
--- a/contrib/postgres_fdw/postgres_fdw.h
+++ b/contrib/postgres_fdw/postgres_fdw.h
@@ -20,6 +20,41 @@
 
 #include "libpq-fe.h"
 
+/*
+ * FDW-specific planner information kept in RelOptInfo.fdw_private for a
+ * foreign table.  This information is collected by postgresGetForeignRelSize.
+ */
+typedef struct PgFdwRelationInfo
+{
+	/* baserestrictinfo clauses, broken down into safe and unsafe subsets. */
+	List	   *remote_conds;
+	List	   *local_conds;
+
+	/* Bitmap of attr numbers we need to fetch from the remote server. */
+	Bitmapset  *attrs_used;
+
+	/* Cost and selectivity of local_conds. */
+	QualCost	local_conds_cost;
+	Selectivity local_conds_sel;
+
+	/* Estimated size and cost for a scan with baserestrictinfo quals. */
+	double		rows;
+	int			width;
+	Cost		startup_cost;
+	Cost		total_cost;
+
+	/* Options extracted from catalogs. */
+	bool		use_remote_estimate;
+	Cost		fdw_startup_cost;
+	Cost		fdw_tuple_cost;
+	List	   *shippable_extensions;	/* OIDs of whitelisted extensions */
+
+	/* Cached catalog information. */
+	ForeignTable *table;
+	ForeignServer *server;
+	UserMapping *user;			/* only set in use_remote_estimate mode */
+} PgFdwRelationInfo;
+
 /* in postgres_fdw.c */
 extern int	set_transmission_modes(void);
 extern void reset_transmission_modes(int nestlevel);
@@ -37,6 +72,8 @@ extern void pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
 extern int ExtractConnectionOptions(List *defelems,
 						 const char **keywords,
 						 const char **values);
+extern List *ExtractExtensionList(const char *extensionsString,
+					 bool warnOnMissing);
 
 /* in deparse.c */
 extern void classifyConditions(PlannerInfo *root,
@@ -76,6 +113,10 @@ extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
 extern void deparseStringLiteral(StringInfo buf, const char *val);
 extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
 extern void appendOrderByClause(StringInfo buf, PlannerInfo *root,
-								RelOptInfo *baserel, List *pathkeys);
+					RelOptInfo *baserel, List *pathkeys);
+
+/* in shippable.c */
+extern bool is_builtin(Oid objectId);
+extern bool is_shippable(Oid objectId, Oid classId, PgFdwRelationInfo *fpinfo);
 
 #endif   /* POSTGRES_FDW_H */