Function RelationBuildPartitionKey

src/backend/utils/cache/partcache.c:80–268

* RelationBuildPartitionKey * Build partition key data of relation, and attach to relcache * * Partitioning key data is a complex structure; to avoid complicated logic to * free individual elements whenever the relcache entry is flushed, we give it * its own memory context, a child of CacheMemoryContext, which can easily be * deleted on its own. To avoid leaking memory in that context in c

 * permanently.
 */
static void
RelationBuildPartitionKey(Relation relation)
{
	Form_pg_partitioned_table form;
	HeapTuple	tuple;
	bool		isnull;
	int			i;
	PartitionKey key;
	AttrNumber *attrs;
	oidvector  *opclass;
	oidvector  *collation;
	ListCell   *partexprs_item;
	Datum		datum;
	MemoryContext partkeycxt,
				oldcxt;
	int16		procnum;

	tuple = SearchSysCache1(PARTRELID,
							ObjectIdGetDatum(RelationGetRelid(relation)));

	if (!HeapTupleIsValid(tuple))
		elog(ERROR, "cache lookup failed for partition key of relation %u",
			 RelationGetRelid(relation));

	partkeycxt = AllocSetContextCreate(CurTransactionContext,
									   "partition key",
									   ALLOCSET_SMALL_SIZES);
	MemoryContextCopyAndSetIdentifier(partkeycxt,
									  RelationGetRelationName(relation));

	key = (PartitionKey) MemoryContextAllocZero(partkeycxt,
												sizeof(PartitionKeyData));

	/* Fixed-length attributes */
	form = (Form_pg_partitioned_table) GETSTRUCT(tuple);
	key->strategy = form->partstrat;
	key->partnatts = form->partnatts;

	/*
	 * We can rely on the first variable-length attribute being mapped to the
	 * relevant field of the catalog's C struct, because all previous
	 * attributes are non-nullable and fixed-length.
	 */
	attrs = form->partattrs.values;

	/* But use the hard way to retrieve further variable-length attributes */
	/* Operator class */
	datum = SysCacheGetAttr(PARTRELID, tuple,
							Anum_pg_partitioned_table_partclass, &isnull);
	Assert(!isnull);
	opclass = (oidvector *) DatumGetPointer(datum);

	/* Collation */
	datum = SysCacheGetAttr(PARTRELID, tuple,
							Anum_pg_partitioned_table_partcollation, &isnull);
	Assert(!isnull);
	collation = (oidvector *) DatumGetPointer(datum);