typedef SlruCtlData *SlruCtl;

/*

* Shared-memorystate

*/

typedef struct SlruSharedData

{

LWLockId ControlLock;

/* Number of buffers managed by this SLRU structure */

int num_slots;

/*

* Arrays holding info for each bufferslot. Page number is undefined

* when status is EMPTY, as is page_lru_count.

*/

char **page_buffer;

SlruPageStatus*page_status;

bool *page_dirty;

int *page_number;

int *page_lru_count;

LWLockId *buffer_locks;

/*----------

* We mark a page "most recentlyused" by setting

* page_lru_count[slotno]= ++cur_lru_count;

* The oldest page is therefore the one withthe highest value of

* cur_lru_count- page_lru_count[slotno]

* The counts will eventually wrap around, butthis calculation still

* works as long as no page's age exceedsINT_MAX counts.

*----------

*/

int cur_lru_count;

/*

* latest_page_number is the page number of thecurrent end of the log;

* this is not critical data, since we use itonly to avoid swapping out

* the latest page.

*/

int latest_page_number;

} SlruSharedData;

typedef SlruSharedData *SlruShared;

下面看看初始化完"CLOG Ctl"相关结构后在内存中的结构图

初始化完clog的内 存结构图

为了精简上图，把创建shmem的哈希表索引"ShmemIndex"时创建的HCTL结构删掉了，这个结构的作用是记录创建可扩展哈希表的相关信息。增加了左边灰色底的部分，描述共享内存/shmem里各变量物理布局概览，由下往上，由低地址到高地址。其中的"CLOG Ctl"即clog的相关结构图下面分别给出，要不上面的图太大太复杂了。

CLOG相关结构图