wiretiger存储引擎源码解读----checkpoint相关数据结构

上图中是为了表现几个数据结构之间的关系，有简化

__wt_ckpt

在src/include/meta.h文件中定义的，是元数据信息相关的结构体
源码中是这个注释的：
Encapsulation of checkpoint information, shared by the metadata, the btree engine, and the block manager.
丰封装了checkpoint信息，共享于元数据、btree引擎、和block manager

struct __wt_ckpt {
   
	char	*name;				/* Name or NULL;  WiredTigerCheckpoint.127594 */

	WT_ITEM  addr;				/* Checkpoint cookie string */
	WT_ITEM  raw;				/* Checkpoint cookie raw */

	int64_t	 order;				/* Checkpoint order */

	uintmax_t sec;				/* Timestamp */

	uint64_t ckpt_size;			/* Checkpoint size */

	uint64_t write_gen;			/* Write generation */

	void	*bpriv;				/* Block manager private */

/* AUTOMATIC FLAG VALUE GENERATION START */
#define	WT_CKPT_ADD	0x1u			/* Checkpoint to be added */
#define	WT_CKPT_DELETE	0x2u			/* Checkpoint to be deleted */
#define	WT_CKPT_FAKE	0x4u			/* Checkpoint is a fake */
#define	WT_CKPT_UPDATE	0x8u			/* Checkpoint requires update */
/* AUTOMATIC FLAG VALUE GENERATION STOP */
	uint32_t flags;
};

__wt_block_ckpt

在src/include/block.h文件中定义的，
源码中是这么注释的：

• Checkpoint cookie: carries a version number as I don’t want to rev the schema
• file version should the default block manager checkpoint format change.
• Version #1 checkpoint cookie format:
• [1] [root addr] [alloc addr] [avail addr] [discard addr]
• [file size] [checkpoint size] [write generation]
  */

struct __wt_block_ckpt {
   
	uint8_t	 version;			/* Version */

	wt_off_t root_offset;			/* The root */
	uint32_t root_checksum, root_size;

	WT_EXTLIST alloc;			/* Extents allocated */
	WT_EXTLIST avail;			/* Extents available */
	WT_EXTLIST discard;			/* Extents discarded */

	wt_off_t   file_size;			/* Checkpoint file size */
	uint64_t   ckpt_size;			/* Checkpoint byte count */

	WT_EXTLIST ckpt_avail;			/* Checkpoint free'd extents */

	/*
	 * Checkpoint archive: the block manager may potentially free a lot of
	 * memory from the allocation and discard extent lists when checkpoint
	 * completes.  Put it off until the checkpoint resolves, that lets the
	 * upper btree layer continue eviction sooner.
	 */
	WT_EXTLIST ckpt_alloc;			/* Checkpoint archive */
	WT_EXTLIST ckpt_discard;		/* Checkpoint archive */
};

__wt_block

在src/include/block.h文件中定义的，
Block manager handle, references a single file.
每一个数据文件对应一个WT_BLOCK

struct __wt_block {
   
	const char *name;		/* Name */ //文件名  数据文件的文件名， xxxx.wt
	uint64_t name_hash;		/* Hash of name */

	/* A list of block manager handles, sharing a file descriptor. */
	uint32_t ref;			/* References */
	TAILQ_ENTRY(__wt_block) q;	/* Linked list of handles */
	TAILQ_ENTRY(__wt_block) hashq;	/* Hashed list of handles */

	WT_FH	*fh;			/* Backing file handle */
	wt_off_t size;			/* File size */  文件大小
	wt_off_t extend_size;		/* File extended size */  当前ckpt的extend_size，也就是文件的有效大小
	wt_off_t extend_len;		/* File extend chunk size */

	/* Configuration information, set when the file is opened. */
	uint32_t allocfirst;		/* Allocation is first-fit */
	uint32_t allocsize;		/* Allocation size */
	size_t	 os_cache;		/* System buffer cache flush max */
	size_t	 os_cache_max;
	size_t	 os_cache_dirty;	/* System buffer cache write max */
	size_t	 os_cache_dirty_max;

	u_int	 block_header;		/* Header length */

	/*
	 * There is only a single checkpoint in a file that can be written.  The
	 * information could logically live in the WT_BM structure, but then we
	 * would be re-creating it every time we opened a new checkpoint and I'd
	 * rather not do that.  So, it's stored here, only accessed by one WT_BM
	 * handle.
	 */
	WT_SPINLOCK	live_lock;	/* Live checkpoint lock */
	WT_BLOCK_CKPT	live;		/* Live checkpoint */  //目前正在使用的ckpt
#ifdef HAVE_DIAGNOSTIC
	bool		live_open;	/* Live system is open */
#endif
					/* Live checkpoint status */
	enum {
    WT_CKPT_NONE=0, WT_CKPT_INPROGRESS,
	    WT_CKPT_PANIC_ON_FAILURE, WT_CKPT_SALVAGE } ckpt_state; //checkpoint的状态

				/* Compaction support */
	int	 compact_pct_tenths;	/* Percent to compact */
	uint64_t compact_pages_reviewed;/* Pages reviewed */
	uint64_t compact_pages_skipped;	/* Pages skipped */
	uint64_t compact_pages_written;	/* Pages rewritten */

				/* Salvage support */
	wt_off_t	slvg_off;	/* Salvage file offset */

				/* Verification support */
	bool	   verify;		/* If performing verification */
	bool	   verify_layout