1 files changed, 252 insertions, 0 deletions
diff --git a/src/backend/utils/adt/partitionfuncs.c b/src/backend/utils/adt/partitionfuncs.c
new file mode 100644
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+++ b/src/backend/utils/adt/partitionfuncs.c
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+/*-------------------------------------------------------------------------
+ *
+ * partitionfuncs.c
+ *	  Functions for accessing partition-related metadata
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/adt/partitionfuncs.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "access/htup_details.h"
+#include "catalog/partition.h"
+#include "catalog/pg_class.h"
+#include "catalog/pg_inherits.h"
+#include "catalog/pg_type.h"
+#include "funcapi.h"
+#include "utils/fmgrprotos.h"
+#include "utils/lsyscache.h"
+#include "utils/syscache.h"
+
+/*
+ * Checks if a given relation can be part of a partition tree.  Returns
+ * false if the relation cannot be processed, in which case it is up to
+ * the caller to decide what to do, by either raising an error or doing
+ * something else.
+ */
+static bool
+check_rel_can_be_partition(Oid relid)
+{
+	char		relkind;
+	bool		relispartition;
+
+	/* Check if relation exists */
+	if (!SearchSysCacheExists1(RELOID, ObjectIdGetDatum(relid)))
+		return false;
+
+	relkind = get_rel_relkind(relid);
+	relispartition = get_rel_relispartition(relid);
+
+	/* Only allow relation types that can appear in partition trees. */
+	if (!relispartition &&
+		relkind != RELKIND_PARTITIONED_TABLE &&
+		relkind != RELKIND_PARTITIONED_INDEX)
+		return false;
+
+	return true;
+}
+
+/*
+ * pg_partition_tree
+ *
+ * Produce a view with one row per member of a partition tree, beginning
+ * from the top-most parent given by the caller.  This gives information
+ * about each partition, its immediate partitioned parent, if it is
+ * a leaf partition and its level in the hierarchy.
+ */
+Datum
+pg_partition_tree(PG_FUNCTION_ARGS)
+{
+#define PG_PARTITION_TREE_COLS	4
+	Oid			rootrelid = PG_GETARG_OID(0);
+	FuncCallContext *funcctx;
+	List	   *partitions;
+
+	/* stuff done only on the first call of the function */
+	if (SRF_IS_FIRSTCALL())
+	{
+		MemoryContext oldcxt;
+		TupleDesc	tupdesc;
+
+		/* create a function context for cross-call persistence */
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		if (!check_rel_can_be_partition(rootrelid))
+			SRF_RETURN_DONE(funcctx);
+
+		/* switch to memory context appropriate for multiple function calls */
+		oldcxt = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+		/*
+		 * Find all members of inheritance set.  We only need AccessShareLock
+		 * on the children for the partition information lookup.
+		 */
+		partitions = find_all_inheritors(rootrelid, AccessShareLock, NULL);
+
+		tupdesc = CreateTemplateTupleDesc(PG_PARTITION_TREE_COLS);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "relid",
+						   REGCLASSOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "parentid",
+						   REGCLASSOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "isleaf",
+						   BOOLOID, -1, 0);
+		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "level",
+						   INT4OID, -1, 0);
+
+		funcctx->tuple_desc = BlessTupleDesc(tupdesc);
+
+		/* The only state we need is the partition list */
+		funcctx->user_fctx = (void *) partitions;
+
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	/* stuff done on every call of the function */
+	funcctx = SRF_PERCALL_SETUP();
+	partitions = (List *) funcctx->user_fctx;
+
+	if (funcctx->call_cntr < list_length(partitions))
+	{
+		Datum		result;
+		Datum		values[PG_PARTITION_TREE_COLS];
+		bool		nulls[PG_PARTITION_TREE_COLS];
+		HeapTuple	tuple;
+		Oid			parentid = InvalidOid;
+		Oid			relid = list_nth_oid(partitions, funcctx->call_cntr);
+		char		relkind = get_rel_relkind(relid);
+		int			level = 0;
+		List	   *ancestors = get_partition_ancestors(relid);
+		ListCell   *lc;
+
+		/*
+		 * Form tuple with appropriate data.
+		 */
+		MemSet(nulls, 0, sizeof(nulls));
+		MemSet(values, 0, sizeof(values));
+
+		/* relid */
+		values[0] = ObjectIdGetDatum(relid);
+
+		/* parentid */
+		if (ancestors != NIL)
+			parentid = linitial_oid(ancestors);
+		if (OidIsValid(parentid))
+			values[1] = ObjectIdGetDatum(parentid);
+		else
+			nulls[1] = true;
+
+		/* isleaf */
+		values[2] = BoolGetDatum(relkind != RELKIND_PARTITIONED_TABLE &&
+								 relkind != RELKIND_PARTITIONED_INDEX);
+
+		/* level */
+		if (relid != rootrelid)
+		{
+			foreach(lc, ancestors)
+			{
+				level++;
+				if (lfirst_oid(lc) == rootrelid)
+					break;
+			}
+		}
+		values[3] = Int32GetDatum(level);
+
+		tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
+		result = HeapTupleGetDatum(tuple);
+		SRF_RETURN_NEXT(funcctx, result);
+	}
+
+	/* done when there are no more elements left */
+	SRF_RETURN_DONE(funcctx);
+}
+
+/*
+ * pg_partition_root
+ *
+ * Returns the top-most parent of the partition tree to which a given
+ * relation belongs, or NULL if it's not (or cannot be) part of any
+ * partition tree.
+ */
+Datum
+pg_partition_root(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+	Oid			rootrelid;
+	List	   *ancestors;
+
+	if (!check_rel_can_be_partition(relid))
+		PG_RETURN_NULL();
+
+	/* fetch the list of ancestors */
+	ancestors = get_partition_ancestors(relid);
+
+	/*
+	 * If the input relation is already the top-most parent, just return
+	 * itself.
+	 */
+	if (ancestors == NIL)
+		PG_RETURN_OID(relid);
+
+	rootrelid = llast_oid(ancestors);
+	list_free(ancestors);
+
+	/*
+	 * "rootrelid" must contain a valid OID, given that the input relation is
+	 * a valid partition tree member as checked above.
+	 */
+	Assert(OidIsValid(rootrelid));
+	PG_RETURN_OID(rootrelid);
+}
+
+/*
+ * pg_partition_ancestors
+ *
+ * Produces a view with one row per ancestor of the given partition,
+ * including the input relation itself.
+ */
+Datum
+pg_partition_ancestors(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+	FuncCallContext *funcctx;
+	List	   *ancestors;
+
+	if (SRF_IS_FIRSTCALL())
+	{
+		MemoryContext oldcxt;
+
+		funcctx = SRF_FIRSTCALL_INIT();
+
+		if (!check_rel_can_be_partition(relid))
+			SRF_RETURN_DONE(funcctx);
+
+		oldcxt = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
+
+		ancestors = get_partition_ancestors(relid);
+		ancestors = lcons_oid(relid, ancestors);
+
+		/* The only state we need is the ancestors list */
+		funcctx->user_fctx = (void *) ancestors;
+
+		MemoryContextSwitchTo(oldcxt);
+	}
+
+	funcctx = SRF_PERCALL_SETUP();
+	ancestors = (List *) funcctx->user_fctx;
+
+	if (funcctx->call_cntr < list_length(ancestors))
+	{
+		Oid			relid = list_nth_oid(ancestors, funcctx->call_cntr);
+
+		SRF_RETURN_NEXT(funcctx, ObjectIdGetDatum(relid));
+	}
+
+	SRF_RETURN_DONE(funcctx);
+}