探索PostgreSQL数据存储存储之数据页

// 创建测试表
perryn_demo=> create table email(id int,name varchar(255));
CREATE TABLE
// 查询的表的OID
perryn_demo=> select oid,relfilenode from pg_class where relname='email';
  oid  | relfilenode 
-------+-------------
 16386 |       16386
(1 row)

// 插入数据
perryn_demo=> insert into email SELECT generate_series(1,200000),repeat(chr(int4(random()*26)+65),200);
INSERT 0 190001

typedef struct PageHeaderData
{
	// 上一次做更改的xlog的lsn号
	PageXLogRecPtr pd_lsn;		
	// 如果设置了page checksum这里就存储了checksun
	uint16		pd_checksum;	
	// flag的设置
	uint16		pd_flags;		
	// 执行free space的偏移量
	LocationIndex pd_lower;		
	// 执行free space的结束位置的偏移量
	LocationIndex pd_upper;		
	// 执行special space的偏移量
	LocationIndex pd_special;	
	// page的版本号
	uint16		pd_pagesize_version;
	// 最旧的xid
	TransactionId pd_prune_xid; 
	// page header的指针数组
	ItemIdData	pd_linp[FLEXIBLE_ARRAY_MEMBER]; 
} PageHeaderData;

typedef PageHeaderData *PageHeader;


typedef struct ItemIdData
{
	// 物理page的偏移量
	unsigned	lp_off:15,		
	// line poiner的状态
				lp_flags:2,		
	// tuple的长度
				lp_len:15;		
} ItemIdData;

typedef ItemIdData *ItemId;

// 包含在tuple header中的信息
typedef struct HeapTupleFields
{
	// 插入事务ID
	TransactionId t_xmin;		
	// 删除事务ID
	TransactionId t_xmax;		

	union
	{
		// 插入或者删除的cmd id
		CommandId	t_cid;		
		TransactionId t_xvac;	/* old-style VACUUM FULL xact ID */
	}			t_field3;
} HeapTupleFields;

// 记录tuple的在位置信息
typedef struct ItemPointerData
{
	
	BlockIdData ip_blkid;
	OffsetNumber ip_posid;
}

typedef struct HeapTupleHeaderData HeapTupleHeaderData;


struct HeapTupleHeaderData
{
	// 每个元组的事务信息/记录的多少列信息
	union
	{
		// tuple事务信息存储在t_heap中
		HeapTupleFields t_heap;
		DatumTupleFields t_datum;
	}			t_choice;

	// 这个tuple的行记录所在的位置信息
	ItemPointerData t_ctid;		/* current TID of this or newer tuple (or a
								 * speculative insertion token) */


// t_infomask2和t_infomask 决定
#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK2 2
	uint16		t_infomask2;	

#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK 3
	uint16		t_infomask;		
// t_hoff 表示行数据所在的位置
#define FIELDNO_HEAPTUPLEHEADERDATA_HOFF 4
	uint8		t_hoff;			

	/* ^ - 23 bytes - ^ */

#define FIELDNO_HEAPTUPLEHEADERDATA_BITS 5
	bits8		t_bits[FLEXIBLE_ARRAY_MEMBER];	/* bitmap of NULLs */

	/* MORE DATA FOLLOWS AT END OF STRUCT */
};

typedef struct TupleDescData
{
	int			natts;			/* number of attributes in the tuple */
	Oid			tdtypeid;		/* composite type ID for tuple type */
	int32		tdtypmod;		/* typmod for tuple type */
	int			tdrefcount;		/* reference count, or -1 if not counting */
	TupleConstr *constr;		/* constraints, or NULL if none */
	/* attrs[N] is the description of Attribute Number N+1 */
	FormData_pg_attribute attrs[FLEXIBLE_ARRAY_MEMBER];
}			TupleDescData;
typedef struct TupleDescData *TupleDesc;