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 */