Restructure index access method API to hide most of it at the C level.

This patch reduces pg_am to just two columns, a name and a handler
function.  All the data formerly obtained from pg_am is now provided
in a C struct returned by the handler function.  This is similar to
the designs we've adopted for FDWs and tablesample methods.  There
are multiple advantages.  For one, the index AM's support functions
are now simple C functions, making them faster to call and much less
error-prone, since the C compiler can now check function signatures.
For another, this will make it far more practical to define index access
methods in installable extensions.

A disadvantage is that SQL-level code can no longer see attributes
of index AMs; in particular, some of the crosschecks in the opr_sanity
regression test are no longer possible from SQL.  We've addressed that
by adding a facility for the index AM to perform such checks instead.
(Much more could be done in that line, but for now we're content if the
amvalidate functions more or less replace what opr_sanity used to do.)
We might also want to expose some sort of reporting functionality, but
this patch doesn't do that.

Alexander Korotkov, reviewed by Petr Jelínek, and rather heavily
editorialized on by me.

1 files changed, 145 insertions, 0 deletions

diff --git a/src/backend/access/gin/ginvalidate.c b/src/backend/access/gin/ginvalidate.c
new file mode 100644
index 00000000000..e934fe824b5
--- /dev/null
+++ b/src/backend/access/gin/ginvalidate.c
@@ -0,0 +1,145 @@
+/*-------------------------------------------------------------------------
+ *
+ * ginvalidate.c
+ *	  Opclass validator for GIN.
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *			src/backend/access/gin/ginvalidate.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/gin_private.h"
+#include "access/htup_details.h"
+#include "catalog/pg_amop.h"
+#include "catalog/pg_amproc.h"
+#include "catalog/pg_opclass.h"
+#include "utils/catcache.h"
+#include "utils/syscache.h"
+
+
+/*
+ * Validator for a GIN opclass.
+ */
+bool
+ginvalidate(Oid opclassoid)
+{
+	HeapTuple	classtup;
+	Form_pg_opclass classform;
+	Oid			opfamilyoid;
+	Oid			opcintype;
+	int			numclassops;
+	int32		classfuncbits;
+	CatCList   *proclist,
+			   *oprlist;
+	int			i;
+
+	/* Fetch opclass information */
+	classtup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opclassoid));
+	if (!HeapTupleIsValid(classtup))
+		elog(ERROR, "cache lookup failed for operator class %u", opclassoid);
+	classform = (Form_pg_opclass) GETSTRUCT(classtup);
+
+	opfamilyoid = classform->opcfamily;
+	opcintype = classform->opcintype;
+
+	ReleaseSysCache(classtup);
+
+	/* Fetch all operators and support functions of the opfamily */
+	oprlist = SearchSysCacheList1(AMOPSTRATEGY, ObjectIdGetDatum(opfamilyoid));
+	proclist = SearchSysCacheList1(AMPROCNUM, ObjectIdGetDatum(opfamilyoid));
+
+	/* We'll track the ops and functions belonging to the named opclass */
+	numclassops = 0;
+	classfuncbits = 0;
+
+	/* Check support functions */
+	for (i = 0; i < proclist->n_members; i++)
+	{
+		HeapTuple	proctup = &proclist->members[i]->tuple;
+		Form_pg_amproc procform = (Form_pg_amproc) GETSTRUCT(proctup);
+
+		/* Check that only allowed procedure numbers exist */
+		if (procform->amprocnum < 1 ||
+			procform->amprocnum > GINNProcs)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("gin opfamily %u contains invalid support number %d for procedure %u",
+							opfamilyoid,
+							procform->amprocnum, procform->amproc)));
+
+		/* Remember functions that are specifically for the named opclass */
+		if (procform->amproclefttype == opcintype &&
+			procform->amprocrighttype == opcintype)
+			classfuncbits |= (1 << procform->amprocnum);
+	}
+
+	/* Check operators */
+	for (i = 0; i < oprlist->n_members; i++)
+	{
+		HeapTuple	oprtup = &oprlist->members[i]->tuple;
+		Form_pg_amop oprform = (Form_pg_amop) GETSTRUCT(oprtup);
+
+		/* TODO: Check that only allowed strategy numbers exist */
+		if (oprform->amopstrategy < 1)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("gin opfamily %u contains invalid strategy number %d for operator %u",
+							opfamilyoid,
+							oprform->amopstrategy, oprform->amopopr)));
+
+		/* gin doesn't support ORDER BY operators */
+		if (oprform->amoppurpose != AMOP_SEARCH ||
+			OidIsValid(oprform->amopsortfamily))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("gin opfamily %u contains invalid ORDER BY specification for operator %u",
+							opfamilyoid, oprform->amopopr)));
+
+		/* Count operators that are specifically for the named opclass */
+		if (oprform->amoplefttype == opcintype &&
+			oprform->amoprighttype == opcintype)
+			numclassops++;
+	}
+
+	/* Check that the named opclass is complete */
+
+	/* XXX needs work: we need to detect applicability of ANYARRAY operators */
+#ifdef NOT_USED
+	if (numclassops == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("gin opclass %u is missing operator(s)",
+						opclassoid)));
+#endif
+
+	for (i = 1; i <= GINNProcs; i++)
+	{
+		if ((classfuncbits & (1 << i)) != 0)
+			continue;			/* got it */
+		if (i == GIN_COMPARE_PARTIAL_PROC)
+			continue;			/* optional method */
+		if (i == GIN_CONSISTENT_PROC || i == GIN_TRICONSISTENT_PROC)
+			continue;			/* don't need to have both, see check below
+								 * loop */
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+			 errmsg("gin opclass %u is missing required support function %d",
+					opclassoid, i)));
+	}
+	if ((classfuncbits & (1 << GIN_CONSISTENT_PROC)) == 0 &&
+		(classfuncbits & (1 << GIN_TRICONSISTENT_PROC)) == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("gin opclass %u is missing required support function",
+						opclassoid)));
+
+	ReleaseCatCacheList(proclist);
+	ReleaseCatCacheList(oprlist);
+
+	return true;
+}