插入数据主要的实现在bufpage.c中，主要的函数是PageAddItemExtended。查看调用栈：

#0  PageAddItemExtended (page=0x7fddcac3cd00 "", item=0x141f540 "34701", 
    size=32, offsetNumber=0, flags=2) at bufpage.c:199
#1  0x00000000004d9e70 in RelationPutHeapTuple (relation=0x7fddda866178, 
    buffer=158, tuple=0x141f528, token=false) at hio.c:53
#2  0x00000000004c76d2 in heap_insert (relation=0x7fddda866178, tup=0x141f528, 
    cid=0, options=0, bistate=0x0) at heapam.c:1913
#3  0x00000000004d3ead in heapam_tuple_insert (relation=0x7fddda866178, 
    slot=0x141f3c8, cid=0, options=0, bistate=0x0) at heapam_handler.c:257
#4  0x00000000006dae8a in table_tuple_insert (rel=0x7fddda866178, 
    slot=0x141f3c8, cid=0, options=0, bistate=0x0)
    at ../../../src/include/access/tableam.h:1140
#5  0x00000000006dbf87 in ExecInsert (mtstate=0x141e8d0, slot=0x141f3c8, 
    planSlot=0x141f3c8, estate=0x141e540, canSetTag=true)
    at nodeModifyTable.c:586
#6  0x00000000006de2fa in ExecModifyTable (pstate=0x141e8d0)
    at nodeModifyTable.c:2215
#7  0x00000000006b2af7 in ExecProcNodeFirst (node=0x141e8d0)
    at execProcnode.c:445
#8  0x00000000006a8cd7 in ExecProcNode (node=0x141e8d0)
    at ../../../src/include/executor/executor.h:239
#9  0x00000000006ab053 in ExecutePlan (estate=0x141e540, planstate=0x141e8d0, 
    use_parallel_mode=false, operation=CMD_INSERT, sendTuples=false, 
    numberTuples=0, direction=ForwardScanDirection, dest=0x1419ff8, 
---Type <return> to continue, or q <return> to quit---
    execute_once=true) at execMain.c:1646
#10 0x00000000006a91b4 in standard_ExecutorRun (queryDesc=0x141d910, 
    direction=ForwardScanDirection, count=0, execute_once=true)
    at execMain.c:364
#11 0x00000000006a9059 in ExecutorRun (queryDesc=0x141d910, 
    direction=ForwardScanDirection, count=0, execute_once=true)
    at execMain.c:308
#12 0x000000000088016a in ProcessQuery (plan=0x1419f18, 
    sourceText=0x13606f0 "insert into test values(123,"abc");", params=0x0, 
    queryEnv=0x0, dest=0x1419ff8, completionTag=0x7ffd63e18570 "")
    at pquery.c:161
#13 0x00000000008818b1 in PortalRunMulti (portal=0x13c6490, isTopLevel=true, 
    setHoldSnapshot=false, dest=0x1419ff8, altdest=0x1419ff8, 
    completionTag=0x7ffd63e18570 "") at pquery.c:1283
#14 0x0000000000880eeb in PortalRun (portal=0x13c6490, 
    count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x1419ff8, 
    altdest=0x1419ff8, completionTag=0x7ffd63e18570 "") at pquery.c:796
#15 0x000000000087b27f in exec_simple_query (
    query_string=0x13606f0 "insert into test values(123,"abc");")
    at postgres.c:1215
#16 0x000000000087f2ff in PostgresMain (argc=1, argv=0x138a5c8, 
    dbname=0x138a490 "postgres", username=0x138a478 "nail") at postgres.c:4247
#17 0x00000000007e6a8e in BackendRun (port=0x1382470) at postmaster.c:4437
#18 0x00000000007e628d in BackendStartup (port=0x1382470) at postmaster.c:4128
#19 0x00000000007e292d in ServerLoop () at postmaster.c:1704
#20 0x00000000007e21ed in PostmasterMain (argc=3, argv=0x135b1b0)
    at postmaster.c:1377
#21 0x000000000070f75d in main (argc=3, argv=0x135b1b0) at main.c:228

代码100分

相关数据结构

代码流程涉及的PageHeader结构体已在之前了解过。PostgreSQL源码学习（1）Page页

代码100分OffsetNumber
PageAddItemExtended(Page page,
					Item item,
					Size size,
					OffsetNumber offsetNumber,
					int flags);

PageAddItemExtended函数

// src/backend/storage/page/bufpage.c

/* 获取最后一个item（行指针）的偏移量的下一个位置 */
limit = OffsetNumberNext(PageGetMaxOffsetNumber(page));

/* 是否由参数指定了偏移量 */
if (OffsetNumberIsValid(offsetNumber))
{
	if ((flags & PAI_OVERWRITE) != 0)
		/* 如果设置了PAI_OVERWRITE，必须检查确保参数指定的offsetNumber
		    指向未使用的item，或指向的位置在最后一个item之后 */
	else
		/* 否则会将item插入到指定位置，如果位置已占，会进行移动以腾出空间 */
}
else
{
	/* 没有参数指定偏移量的话，就寻找一个未使用并且已释放的slot，
	    若没有已释放的slot，就指定偏移量为limit，将数据存入free space中 */
}

if ((flags & PAI_IS_HEAP) != 0 && offsetNumber > MaxHeapTuplesPerPage)
	/* 如果指定了PAI_IS_HEAP，那么存储的位置不能超过此限制 */;

/* 计算新的或复用pd_lower和pd_upper（略） */

if (needshuffle)
	/* 使用memmove对现有的行指针进行移动 */
	memmove(itemId + 1, itemId,
				(limit - offsetNumber) * sizeof(ItemIdData));

/* 设置新数据的行指针（ItemData） */
ItemIdSetNormal(itemId, upper, size);

/* 使用memcpy拷贝数据到page页中的指定位置 */
memcpy((char *) page + upper, item, size);

/* 调整page header的信息（略) */

/* 返回新数据的偏移量 */
return offsetNumber;