postgressql——ReadBuffer_common函数（7）

PostgreSQL中ReadBuffer_common函数

数据结构

BufferDesc
共享缓冲区的共享描述符(状态)数据

typedef struct BufferDesc
{//buffer tagBufferTag   tag;            /* ID of page contained in buffer *///buffer索引编号(0开始)int         buf_id;         /* buffer's index number (from 0) *//* state of the tag, containing flags, refcount and usagecount *///tag状态,包括flags/refcount和usagecountpg_atomic_uint32 state;//pin-count等待进程IDint         wait_backend_pid;   /* backend PID of pin-count waiter *///空闲链表链中下一个空闲的bufferint         freeNext;       /* link in freelist chain *///缓冲区内容锁LWLock      content_lock;   /* to lock access to buffer contents */
} BufferDesc;

BufferTag
Buffer tag标记了buffer存储的是磁盘中哪个block

typedef struct buftag
{//物理relation标识符RelFileNode rnode;          /* physical relation identifier */ForkNu