pg共享内存

基本数据结构

• PGShmemHeader

typedef struct PGShmemHeader	/* standard header for all Postgres shmem */
{
  int32		magic;			/* magic # to identify Postgres segments */
#define PGShmemMagic  679834894
  pid_t		creatorPID;		/* PID of creating process (set but unread) */
  Size		totalsize;		/* total size of segment */
  Size		freeoffset;		/* offset to first free space */
  dsm_handle	dsm_control;	/* ID of dynamic shared memory control seg */
  void	   *index;			/* pointer to ShmemIndex table */
#ifndef WIN32					/* Windows doesn't have useful inode#s */
  dev_t		device;			/* device data directory is on */
  ino_t		inode;			/* inode number of data directory */
#endif
} PGShmemHeader;

• ShmemIndexEnt

/* this is a hash bucket in the shmem index table */
typedef struct
{
  char		key[SHMEM_INDEX_KEYSIZE];	/* string name */
  void	   *location;		/* location in shared mem */
  Size		size;			/* # bytes requested for the structure */
  Size		allocated_size; /* # bytes actually allocated */
} ShmemIndexEnt;

初始化

• 全局变量

static HTAB *ShmemIndex = NULL; /* primary index hashtable for shmem */

处理逻辑

对外接口