PostgreSQL源码学习更新数据#1，2

Z时代
2024-01-10
分类：综合

database

本节介绍heapam_tuple_update和table_tuple_update函数。

heapam_tuple_update函数

//src/backend/access/heap/heapam_handler.c
static TM_Result
heapam_tuple_update(Relation relation, ItemPointer otid, TupleTableSlot *slot,
					CommandId cid, Snapshot snapshot, Snapshot crosscheck,
					bool wait, TM_FailureData *tmfd,
					LockTupleMode *lockmode, bool *update_indexes)
{
	bool		shouldFree = true;
	HeapTuple	tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
	TM_Result	result;
	/* 设置tableoid */
	slot->tts_tableOid = RelationGetRelid(relation);
	tuple->t_tableOid = slot->tts_tableOid;
	result = heap_update(relation, otid, tuple, cid, crosscheck, wait,
						 tmfd, lockmode);
	/* 复制新tuple的tid到slot的tts_tid中 */
	ItemPointerCopy(&tuple->t_self, &slot->tts_tid);
	/* 判断新的元组是否需要索引节点（用了HOT就不需要）*/
	*update_indexes = result == TM_Ok && !HeapTupleIsHeapOnly(tuple);
	if (shouldFree)
		pfree(tuple);
	return result;
}

table_tuple_update函数

//src/include/access/tableam.h
static inline TM_Result
table_tuple_update(Relation rel, ItemPointer otid, TupleTableSlot *slot,
			   CommandId cid, Snapshot snapshot, Snapshot crosscheck,
			   bool wait, TM_FailureData *tmfd, LockTupleMode *lockmode,
			   bool *update_indexes)
{
	/* 默认的表存储引擎的话，rd_tableam赋值为heapam_methods，
	   其tuple_update指向的就是heapam_tuple_update函数 */
	return rel->rd_tableam->tuple_update(rel, otid, slot,
						 cid, snapshot, crosscheck,
						 wait, tmfd,
						 lockmode, update_indexes);
}