大家好，我是考100分的小小码 ，祝大家学习进步，加薪顺利呀。今天说一说PostgreSQL源码学习（1）Page页,希望您对编程的造诣更进一步.
The Internals of PostgreSQL中对于存储的描述http://www.interdb.jp/pg/pgsql01.html#_1.2.
每个表或索引都作为一个page数组存储于物理数据文件中（page大小默认为8k，编译时可以指定），单个的表数据文件中包含多个page页（默认单个表文件最大1G，超过1G后会新建同名+“.1”后缀的数据文件，依次累加，同样在编译时可以指定单个文件的最大值）。page页的结构如下图所示。
而对于page页中存储的行数据Tuple，其结构为下图所示。
相关数据结构
// src/include/storage/bufpage.h
typedef struct PageHeaderData
{
/* XXX LSN is member of *any* block, not only page-organized ones */
PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog
* record for last change to this page */
uint16 pd_checksum; /* checksum */
uint16 pd_flags; /* flag bits, see below */
LocationIndex pd_lower; /* offset to start of free space */
LocationIndex pd_upper; /* offset to end of free space */
LocationIndex pd_special; /* offset to start of special space */
uint16 pd_pagesize_version;
TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */
ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]; /* line pointer array */
} PageHeaderData;
代码100分
代码100分// src/include/storage/itemid.h
typedef struct ItemIdData
{
unsigned lp_off:15, /* offset to tuple (from start of page) */
lp_flags:2, /* state of line pointer, see below */
lp_len:15; /* byte length of tuple */
} ItemIdData;
/*
* lp_flags has these possible states. An UNUSED line pointer is available
* for immediate re-use, the other states are not.
*/
#define LP_UNUSED 0 /* unused (should always have lp_len=0) */
#define LP_NORMAL 1 /* used (should always have lp_len>0) */
#define LP_REDIRECT 2 /* HOT redirect (should have lp_len=0) */
#define LP_DEAD 3 /* dead, may or may not have storage */
// src/include/access/htup_details.h
struct HeapTupleHeaderData
{
union
{
HeapTupleFields t_heap;
DatumTupleFields t_datum;
} t_choice;
ItemPointerData t_ctid; /* current TID of this or newer tuple (or a
* speculative insertion token) */
/* Fields below here must match MinimalTupleData! */
#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK2 2
uint16 t_infomask2; /* number of attributes + various flags */
#define FIELDNO_HEAPTUPLEHEADERDATA_INFOMASK 3
uint16 t_infomask; /* various flag bits, see below */
#define FIELDNO_HEAPTUPLEHEADERDATA_HOFF 4
uint8 t_hoff; /* sizeof header incl. bitmap, padding */
/* ^ - 23 bytes - ^ */
#define FIELDNO_HEAPTUPLEHEADERDATA_BITS 5
bits8 t_bits[FLEXIBLE_ARRAY_MEMBER]; /* bitmap of NULLs */
/* MORE DATA FOLLOWS AT END OF STRUCT */
};
代码100分// src/include/access/htup.h
typedef struct HeapTupleData
{
uint32 t_len; /* length of *t_data */
ItemPointerData t_self; /* SelfItemPointer */
Oid t_tableOid; /* table the tuple came from */
#define FIELDNO_HEAPTUPLEDATA_DATA 3
HeapTupleHeader t_data; /* -> tuple header and data */
} HeapTupleData;
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