mariadb/include/buf0buf.h

/*   Innobase relational database engine; Copyright (C) 2001 Innobase Oy

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License 2
     as published by the Free Software Foundation in June 1991.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License 2
     along with this program (in file COPYING); if not, write to the Free
     Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */
/******************************************************
The database buffer pool high-level routines

(c) 1995 Innobase Oy

Created 11/5/1995 Heikki Tuuri
*******************************************************/

#ifndef buf0buf_h
#define buf0buf_h

#include "univ.i"
#include "fil0fil.h"
#include "mtr0types.h"
#include "buf0types.h"
#include "sync0rw.h"
#include "hash0hash.h"
#include "ut0byte.h"
#include "ut0rbt.h"
#include "os0proc.h"
#include "page0types.h"

/* Modes for buf_page_get_gen */
#define BUF_GET			10	/* get always */
#define	BUF_GET_IF_IN_POOL	11	/* get if in pool */
#define BUF_GET_NO_LATCH	14	/* get and bufferfix, but set no latch;
					we have separated this case, because
					it is error-prone programming not to
					set a latch, and it should be used
					with care */
#define BUF_GET_IF_IN_POOL_OR_WATCH	15
					/* Get the page only if it's in the
					buffer pool, if not then set a watch
					on the page. */
/* Modes for buf_page_get_known_nowait */
#define BUF_MAKE_YOUNG	51
#define BUF_KEEP_OLD	52
/* Magic value to use instead of checksums when they are disabled */
#define BUF_NO_CHECKSUM_MAGIC 0xDEADBEEFUL

extern buf_pool_t*	buf_pool;	/* The buffer pool of the database */
#ifdef UNIV_DEBUG
extern ibool		buf_debug_prints;/* If this is set TRUE, the program
					prints info whenever read or flush
					occurs */
#endif /* UNIV_DEBUG */
extern ulint srv_buf_pool_write_requests; /* variable to count write request
					  issued */

/* States of a control block (@see buf_page_struct).
The enumeration values must be 0..7. */
enum buf_page_state {
	BUF_BLOCK_ZIP_FREE = 0,		/* contains a free compressed page */
	BUF_BLOCK_ZIP_PAGE,		/* contains a clean compressed page */
	BUF_BLOCK_ZIP_DIRTY,		/* contains a compressed page that is
					in the buf_pool->flush_list */

	/* The constants for compressed-only pages must precede
	BUF_BLOCK_NOT_USED; @see buf_block_state_valid() */

	BUF_BLOCK_NOT_USED,		/* is in the free list */
	BUF_BLOCK_READY_FOR_USE,	/* when buf_LRU_get_free_block returns
					a block, it is in this state */
	BUF_BLOCK_FILE_PAGE,		/* contains a buffered file page */
	BUF_BLOCK_MEMORY,		/* contains some main memory object */
	BUF_BLOCK_REMOVE_HASH		/* hash index should be removed
					before putting to the free list */
};

/************************************************************************
Creates the buffer pool. */
UNIV_INTERN
buf_pool_t*
buf_pool_init(void);
/*===============*/
				/* out, own: buf_pool object, NULL if not
				enough memory or error */
/************************************************************************
Frees the buffer pool at shutdown.  This must not be invoked before
freeing all mutexes. */
UNIV_INTERN
void
buf_pool_free(void);
/*===============*/

/************************************************************************
Relocate a buffer control block.  Relocates the block on the LRU list
and in buf_pool->page_hash.  Does not relocate bpage->list.
The caller must take care of relocating bpage->list. */
UNIV_INTERN
void
buf_relocate(
/*=========*/
	buf_page_t*	bpage,	/* in/out: control block being relocated;
				buf_page_get_state(bpage) must be
				BUF_BLOCK_ZIP_DIRTY or BUF_BLOCK_ZIP_PAGE */
	buf_page_t*	dpage)	/* in/out: destination control block */
	__attribute__((nonnull));
/************************************************************************
Resizes the buffer pool. */
UNIV_INTERN
void
buf_pool_resize(void);
/*=================*/
/*************************************************************************
Gets the current size of buffer buf_pool in bytes. */
UNIV_INLINE
ulint
buf_pool_get_curr_size(void);
/*========================*/
			/* out: size in bytes */
/************************************************************************
Gets the smallest oldest_modification lsn for any page in the pool. Returns
zero if all modified pages have been flushed to disk. */
UNIV_INLINE
ib_uint64_t
buf_pool_get_oldest_modification(void);
/*==================================*/
				/* out: oldest modification in pool,
				zero if none */
/************************************************************************
Allocates a buffer block. */
UNIV_INLINE
buf_block_t*
buf_block_alloc(
/*============*/
				/* out, own: the allocated block,
				in state BUF_BLOCK_MEMORY */
	ulint	zip_size);	/* in: compressed page size in bytes,
				or 0 if uncompressed tablespace */
/************************************************************************
Frees a buffer block which does not contain a file page. */
UNIV_INLINE
void
buf_block_free(
/*===========*/
	buf_block_t*	block);	/* in, own: block to be freed */
/*************************************************************************
Copies contents of a buffer frame to a given buffer. */
UNIV_INLINE
byte*
buf_frame_copy(
/*===========*/
					/* out: buf */
	byte*			buf,	/* in: buffer to copy to */
	const buf_frame_t*	frame);	/* in: buffer frame */
/******************************************************************
NOTE! The following macros should be used instead of buf_page_get_gen,
to improve debugging. Only values RW_S_LATCH and RW_X_LATCH are allowed
in LA! */
#define buf_page_get(SP, ZS, OF, LA, MTR)	 buf_page_get_gen(\
				SP, ZS, OF, LA, NULL,\
				BUF_GET, __FILE__, __LINE__, MTR)
/******************************************************************
Use these macros to bufferfix a page with no latching. Remember not to
read the contents of the page unless you know it is safe. Do not modify
the contents of the page! We have separated this case, because it is
error-prone programming not to set a latch, and it should be used
with care. */
#define buf_page_get_with_no_latch(SP, ZS, OF, MTR)	   buf_page_get_gen(\
				SP, ZS, OF, RW_NO_LATCH, NULL,\
				BUF_GET_NO_LATCH, __FILE__, __LINE__, MTR)
/******************************************************************
NOTE! The following macros should be used instead of
buf_page_optimistic_get_func, to improve debugging. Only values RW_S_LATCH and
RW_X_LATCH are allowed as LA! */
#define buf_page_optimistic_get(LA, BL, MC, MTR)			     \
	buf_page_optimistic_get_func(LA, BL, MC, __FILE__, __LINE__, MTR)
/************************************************************************
This is the general function used to get optimistic access to a database
page. */
UNIV_INTERN
ibool
buf_page_optimistic_get_func(
/*=========================*/
				/* out: TRUE if success */
	ulint		rw_latch,/* in: RW_S_LATCH, RW_X_LATCH */
	buf_block_t*	block,	/* in: guessed block */
	ib_uint64_t	modify_clock,/* in: modify clock value if mode is
				..._GUESS_ON_CLOCK */
	const char*	file,	/* in: file name */
	ulint		line,	/* in: line where called */
	mtr_t*		mtr);	/* in: mini-transaction */
/************************************************************************
This is used to get access to a known database page, when no waiting can be
done. */
UNIV_INTERN
ibool
buf_page_get_known_nowait(
/*======================*/
				/* out: TRUE if success */
	ulint		rw_latch,/* in: RW_S_LATCH, RW_X_LATCH */
	buf_block_t*	block,	/* in: the known page */
	ulint		mode,	/* in: BUF_MAKE_YOUNG or BUF_KEEP_OLD */
	const char*	file,	/* in: file name */
	ulint		line,	/* in: line where called */
	mtr_t*		mtr);	/* in: mini-transaction */

/***********************************************************************
Given a tablespace id and page number tries to get that page. If the
page is not in the buffer pool it is not loaded and NULL is returned.
Suitable for using when holding the kernel mutex. */

const buf_block_t*
buf_page_try_get_func(
/*==================*/
	ulint		space_id,/* in: tablespace id */
	ulint		page_no,/* in: page number */
	const char*	file,	/* in: file name */
	ulint		line,	/* in: line where called */
	mtr_t*		mtr);	/* in: mini-transaction */

#define buf_page_try_get(space_id, page_no, mtr)	\
	buf_page_try_get_func(space_id, page_no, __FILE__, __LINE__, mtr);

/************************************************************************
Get read access to a compressed page (usually of type
FIL_PAGE_TYPE_ZBLOB or FIL_PAGE_TYPE_ZBLOB2).
The page must be released with buf_page_release_zip().
NOTE: the page is not protected by any latch.  Mutual exclusion has to
be implemented at a higher level.  In other words, all possible
accesses to a given page through this function must be protected by
the same set of mutexes or latches. */
UNIV_INTERN
buf_page_t*
buf_page_get_zip(
/*=============*/
				/* out: pointer to the block,
				or NULL if not compressed */
	ulint		space,	/* in: space id */
	ulint		zip_size,/* in: compressed page size */
	ulint		offset);/* in: page number */
/************************************************************************
This is the general function used to get access to a database page. */
UNIV_INTERN
buf_block_t*
buf_page_get_gen(
/*=============*/
				/* out: pointer to the block or NULL */
	ulint		space,	/* in: space id */
	ulint		zip_size,/* in: compressed page size in bytes
				or 0 for uncompressed pages */
	ulint		offset,	/* in: page number */
	ulint		rw_latch,/* in: RW_S_LATCH, RW_X_LATCH, RW_NO_LATCH */
	buf_block_t*	guess,	/* in: guessed block or NULL */
	ulint		mode,	/* in: BUF_GET, BUF_GET_IF_IN_POOL,
				BUF_GET_NO_LATCH, BUF_GET_NOWAIT or
				BUF_GET_IF_IN_POOL_WATCH */
	const char*	file,	/* in: file name */
	ulint		line,	/* in: line where called */
	mtr_t*		mtr);	/* in: mini-transaction */
/************************************************************************
Initializes a page to the buffer buf_pool. The page is usually not read
from a file even if it cannot be found in the buffer buf_pool. This is one
of the functions which perform to a block a state transition NOT_USED =>
FILE_PAGE (the other is buf_page_get_gen). */
UNIV_INTERN
buf_block_t*
buf_page_create(
/*============*/
			/* out: pointer to the block, page bufferfixed */
	ulint	space,	/* in: space id */
	ulint	offset,	/* in: offset of the page within space in units of
			a page */
	ulint	zip_size,/* in: compressed page size, or 0 */
	mtr_t*	mtr);	/* in: mini-transaction handle */
#ifdef UNIV_HOTBACKUP
/************************************************************************
Inits a page to the buffer buf_pool, for use in ibbackup --restore. */
UNIV_INTERN
void
buf_page_init_for_backup_restore(
/*=============================*/
	ulint		space,	/* in: space id */
	ulint		offset,	/* in: offset of the page within space
				in units of a page */
	ulint		zip_size,/* in: compressed page size in bytes
				or 0 for uncompressed pages */
	buf_block_t*	block);	/* in: block to init */
#endif /* UNIV_HOTBACKUP */
/************************************************************************
Releases a compressed-only page acquired with buf_page_get_zip(). */
UNIV_INLINE
void
buf_page_release_zip(
/*=================*/
	buf_page_t*	bpage);		/* in: buffer block */
/************************************************************************
Decrements the bufferfix count of a buffer control block and releases
a latch, if specified. */
UNIV_INLINE
void
buf_page_release(
/*=============*/
	buf_block_t*	block,		/* in: buffer block */
	ulint		rw_latch,	/* in: RW_S_LATCH, RW_X_LATCH,
					RW_NO_LATCH */
	mtr_t*		mtr);		/* in: mtr */
/************************************************************************
Moves a page to the start of the buffer pool LRU list. This high-level
function can be used to prevent an important page from from slipping out of
the buffer pool. */
UNIV_INTERN
void
buf_page_make_young(
/*================*/
	buf_page_t*	bpage);	/* in: buffer block of a file page */
/************************************************************************
Returns TRUE if the page can be found in the buffer pool hash table. NOTE
that it is possible that the page is not yet read from disk, though. */
UNIV_INLINE
ibool
buf_page_peek(
/*==========*/
			/* out: TRUE if found from page hash table,
			NOTE that the page is not necessarily yet read
			from disk! */
	ulint	space,	/* in: space id */
	ulint	offset);/* in: page number */
/************************************************************************
Resets the check_index_page_at_flush field of a page if found in the buffer
pool. */
UNIV_INTERN
void
buf_reset_check_index_page_at_flush(
/*================================*/
	ulint	space,	/* in: space id */
	ulint	offset);/* in: page number */
#ifdef UNIV_DEBUG_FILE_ACCESSES
/************************************************************************
Sets file_page_was_freed TRUE if the page is found in the buffer pool.
This function should be called when we free a file page and want the
debug version to check that it is not accessed any more unless
reallocated. */
UNIV_INTERN
buf_page_t*
buf_page_set_file_page_was_freed(
/*=============================*/
			/* out: control block if found in page hash table,
			otherwise NULL */
	ulint	space,	/* in: space id */
	ulint	offset);/* in: page number */
/************************************************************************
Sets file_page_was_freed FALSE if the page is found in the buffer pool.
This function should be called when we free a file page and want the
debug version to check that it is not accessed any more unless
reallocated. */
UNIV_INTERN
buf_page_t*
buf_page_reset_file_page_was_freed(
/*===============================*/
			/* out: control block if found in page hash table,
			otherwise NULL */
	ulint	space,	/* in: space id */
	ulint	offset);	/* in: page number */
#endif /* UNIV_DEBUG_FILE_ACCESSES */
/************************************************************************
Reads the freed_page_clock of a buffer block. */
UNIV_INLINE
ulint
buf_page_get_freed_page_clock(
/*==========================*/
					/* out: freed_page_clock */
	const buf_page_t*	bpage)	/* in: block */
	__attribute__((pure));
/************************************************************************
Reads the freed_page_clock of a buffer block. */
UNIV_INLINE
ulint
buf_block_get_freed_page_clock(
/*===========================*/
					/* out: freed_page_clock */
	const buf_block_t*	block)	/* in: block */
	__attribute__((pure));

/************************************************************************
Recommends a move of a block to the start of the LRU list if there is danger
of dropping from the buffer pool. NOTE: does not reserve the buffer pool
mutex. */
UNIV_INLINE
ibool
buf_page_peek_if_too_old(
/*=====================*/
					/* out: TRUE if should be made
					younger */
	const buf_page_t*	bpage);	/* in: block to make younger */
/************************************************************************
Returns the current state of is_hashed of a page. FALSE if the page is
not in the pool. NOTE that this operation does not fix the page in the
pool if it is found there. */
UNIV_INTERN
ibool
buf_page_peek_if_search_hashed(
/*===========================*/
			/* out: TRUE if page hash index is built in search
			system */
	ulint	space,	/* in: space id */
	ulint	offset);/* in: page number */
/************************************************************************
Gets the youngest modification log sequence number for a frame.
Returns zero if not file page or no modification occurred yet. */
UNIV_INLINE
ib_uint64_t
buf_page_get_newest_modification(
/*=============================*/
					/* out: newest modification to page */
	const buf_page_t*	bpage);	/* in: block containing the
					page frame */
/************************************************************************
Increments the modify clock of a frame by 1. The caller must (1) own the
buf_pool mutex and block bufferfix count has to be zero, (2) or own an x-lock
on the block. */
UNIV_INLINE
void
buf_block_modify_clock_inc(
/*=======================*/
	buf_block_t*	block);	/* in: block */
/************************************************************************
Returns the value of the modify clock. The caller must have an s-lock
or x-lock on the block. */
UNIV_INLINE
ib_uint64_t
buf_block_get_modify_clock(
/*=======================*/
				/* out: value */
	buf_block_t*	block);	/* in: block */
/************************************************************************
Calculates a page checksum which is stored to the page when it is written
to a file. Note that we must be careful to calculate the same value
on 32-bit and 64-bit architectures. */
UNIV_INTERN
ulint
buf_calc_page_new_checksum(
/*=======================*/
				/* out: checksum */
	const byte*	page);	/* in: buffer page */
/************************************************************************
In versions < 4.0.14 and < 4.1.1 there was a bug that the checksum only
looked at the first few bytes of the page. This calculates that old
checksum.
NOTE: we must first store the new formula checksum to
FIL_PAGE_SPACE_OR_CHKSUM before calculating and storing this old checksum
because this takes that field as an input! */
UNIV_INTERN
ulint
buf_calc_page_old_checksum(
/*=======================*/
				/* out: checksum */
	const byte*	 page);	/* in: buffer page */
/************************************************************************
Checks if a page is corrupt. */
UNIV_INTERN
ibool
buf_page_is_corrupted(
/*==================*/
					/* out: TRUE if corrupted */
	const byte*	read_buf,	/* in: a database page */
	ulint		zip_size);	/* in: size of compressed page;
					0 for uncompressed pages */
/**************************************************************************
Gets the space id, page offset, and byte offset within page of a
pointer pointing to a buffer frame containing a file page. */
UNIV_INLINE
void
buf_ptr_get_fsp_addr(
/*=================*/
	const void*	ptr,	/* in: pointer to a buffer frame */
	ulint*		space,	/* out: space id */
	fil_addr_t*	addr);	/* out: page offset and byte offset */
/**************************************************************************
Gets the hash value of a block. This can be used in searches in the
lock hash table. */
UNIV_INLINE
ulint
buf_block_get_lock_hash_val(
/*========================*/
					/* out: lock hash value */
	const buf_block_t*	block)	/* in: block */
	__attribute__((pure));
#ifdef UNIV_DEBUG
/*************************************************************************
Finds a block in the buffer pool that points to a
given compressed page. */
UNIV_INTERN
buf_block_t*
buf_pool_contains_zip(
/*==================*/
				/* out: buffer block pointing to
				the compressed page, or NULL */
	const void*	data);	/* in: pointer to compressed page */
#endif /* UNIV_DEBUG */
#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/*************************************************************************
Validates the buffer pool data structure. */
UNIV_INTERN
ibool
buf_validate(void);
/*==============*/
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
#if defined UNIV_DEBUG_PRINT || defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/*************************************************************************
Prints info of the buffer pool data structure. */
UNIV_INTERN
void
buf_print(void);
/*============*/
#endif /* UNIV_DEBUG_PRINT || UNIV_DEBUG || UNIV_BUF_DEBUG */
/************************************************************************
Prints a page to stderr. */
UNIV_INTERN
void
buf_page_print(
/*===========*/
	const byte*	read_buf,	/* in: a database page */
	ulint		zip_size);	/* in: compressed page size, or
					0 for uncompressed pages */
#ifdef UNIV_DEBUG
/*************************************************************************
Returns the number of latched pages in the buffer pool. */
UNIV_INTERN
ulint
buf_get_latched_pages_number(void);
/*==============================*/
#endif /* UNIV_DEBUG */
/*************************************************************************
Returns the number of pending buf pool ios. */
UNIV_INTERN
ulint
buf_get_n_pending_ios(void);
/*=======================*/
/*************************************************************************
Prints info of the buffer i/o. */
UNIV_INTERN
void
buf_print_io(
/*=========*/
	FILE*	file);	/* in: file where to print */
/*************************************************************************
Returns the ratio in percents of modified pages in the buffer pool /
database pages in the buffer pool. */
UNIV_INTERN
ulint
buf_get_modified_ratio_pct(void);
/*============================*/
/**************************************************************************
Refreshes the statistics used to print per-second averages. */
UNIV_INTERN
void
buf_refresh_io_stats(void);
/*======================*/
/*************************************************************************
Checks that all file pages in the buffer are in a replaceable state. */
UNIV_INTERN
ibool
buf_all_freed(void);
/*===============*/
/*************************************************************************
Checks that there currently are no pending i/o-operations for the buffer
pool. */
UNIV_INTERN
ibool
buf_pool_check_no_pending_io(void);
/*==============================*/
				/* out: TRUE if there is no pending i/o */
/*************************************************************************
Invalidates the file pages in the buffer pool when an archive recovery is
completed. All the file pages buffered must be in a replaceable state when
this function is called: not latched and not modified. */
UNIV_INTERN
void
buf_pool_invalidate(void);
/*=====================*/

/*========================================================================
--------------------------- LOWER LEVEL ROUTINES -------------------------
=========================================================================*/

#ifdef UNIV_SYNC_DEBUG
/*************************************************************************
Adds latch level info for the rw-lock protecting the buffer frame. This
should be called in the debug version after a successful latching of a
page if we know the latching order level of the acquired latch. */
UNIV_INLINE
void
buf_block_dbg_add_level(
/*====================*/
	buf_block_t*	block,	/* in: buffer page
				where we have acquired latch */
	ulint		level);	/* in: latching order level */
#else /* UNIV_SYNC_DEBUG */
# define buf_block_dbg_add_level(block, level) /* nothing */
#endif /* UNIV_SYNC_DEBUG */
/*************************************************************************
Gets the state of a block. */
UNIV_INLINE
enum buf_page_state
buf_page_get_state(
/*===============*/
					/* out: state */
	const buf_page_t*	bpage);	/* in: pointer to the control block */
/*************************************************************************
Gets the state of a block. */
UNIV_INLINE
enum buf_page_state
buf_block_get_state(
/*================*/
					/* out: state */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Sets the state of a block. */
UNIV_INLINE
void
buf_page_set_state(
/*===============*/
	buf_page_t*		bpage,	/* in/out: pointer to control block */
	enum buf_page_state	state);	/* in: state */
/*************************************************************************
Sets the state of a block. */
UNIV_INLINE
void
buf_block_set_state(
/*================*/
	buf_block_t*		block,	/* in/out: pointer to control block */
	enum buf_page_state	state);	/* in: state */
/*************************************************************************
Determines if a block is mapped to a tablespace. */
UNIV_INLINE
ibool
buf_page_in_file(
/*=============*/
					/* out: TRUE if mapped */
	const buf_page_t*	bpage)	/* in: pointer to control block */
	__attribute__((pure));
/*************************************************************************
Determines if a block should be on unzip_LRU list. */
UNIV_INLINE
ibool
buf_page_belongs_to_unzip_LRU(
/*==========================*/
					/* out: TRUE if block belongs
					to unzip_LRU */
	const buf_page_t*	bpage)	/* in: pointer to control block */
	__attribute__((pure));
/*************************************************************************
Determine the approximate LRU list position of a block. */
UNIV_INLINE
ulint
buf_page_get_LRU_position(
/*======================*/
					/* out: LRU list position */
	const buf_page_t*	bpage)	/* in: control block */
	__attribute__((pure));

/*************************************************************************
Gets the mutex of a block. */
UNIV_INLINE
mutex_t*
buf_page_get_mutex(
/*===============*/
					/* out: pointer to mutex
					protecting bpage */
	const buf_page_t*	bpage)	/* in: pointer to control block */
	__attribute__((pure));

/*************************************************************************
Get the flush type of a page. */
UNIV_INLINE
enum buf_flush
buf_page_get_flush_type(
/*====================*/
					/* out: flush type */
	const buf_page_t*	bpage)	/* in: buffer page */
	__attribute__((pure));
/*************************************************************************
Set the flush type of a page. */
UNIV_INLINE
void
buf_page_set_flush_type(
/*====================*/
	buf_page_t*	bpage,		/* in: buffer page */
	enum buf_flush	flush_type);	/* in: flush type */
/*************************************************************************
Map a block to a file page. */
UNIV_INLINE
void
buf_block_set_file_page(
/*====================*/
	buf_block_t*		block,	/* in/out: pointer to control block */
	ulint			space,	/* in: tablespace id */
	ulint			page_no);/* in: page number */
/*************************************************************************
Gets the io_fix state of a block. */
UNIV_INLINE
enum buf_io_fix
buf_page_get_io_fix(
/*================*/
					/* out: io_fix state */
	const buf_page_t*	bpage)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the io_fix state of a block. */
UNIV_INLINE
enum buf_io_fix
buf_block_get_io_fix(
/*================*/
					/* out: io_fix state */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Sets the io_fix state of a block. */
UNIV_INLINE
void
buf_page_set_io_fix(
/*================*/
	buf_page_t*	bpage,	/* in/out: control block */
	enum buf_io_fix	io_fix);/* in: io_fix state */
/*************************************************************************
Sets the io_fix state of a block. */
UNIV_INLINE
void
buf_block_set_io_fix(
/*=================*/
	buf_block_t*	block,	/* in/out: control block */
	enum buf_io_fix	io_fix);/* in: io_fix state */

/************************************************************************
Determine if a buffer block can be relocated in memory.  The block
can be dirty, but it must not be I/O-fixed or bufferfixed. */
UNIV_INLINE
ibool
buf_page_can_relocate(
/*==================*/
	const buf_page_t*	bpage)	/* control block being relocated */
	__attribute__((pure));

/*************************************************************************
Determine if a block has been flagged old. */
UNIV_INLINE
ibool
buf_page_is_old(
/*============*/
					/* out: TRUE if old */
	const buf_page_t*	bpage)	/* in: control block */
	__attribute__((pure));
/*************************************************************************
Flag a block old. */
UNIV_INLINE
void
buf_page_set_old(
/*=============*/
	buf_page_t*	bpage,	/* in/out: control block */
	ibool		old);	/* in: old */
/*************************************************************************
Determine if a block has been accessed in the buffer pool. */
UNIV_INLINE
ibool
buf_page_is_accessed(
/*=================*/
					/* out: TRUE if accessed */
	const buf_page_t*	bpage)	/* in: control block */
	__attribute__((pure));
/*************************************************************************
Flag a block accessed. */
UNIV_INLINE
void
buf_page_set_accessed(
/*==================*/
	buf_page_t*	bpage,		/* in/out: control block */
	ibool		accessed);	/* in: accessed */
/*************************************************************************
Gets the buf_block_t handle of a buffered file block if an uncompressed
page frame exists, or NULL. */
UNIV_INLINE
buf_block_t*
buf_page_get_block(
/*===============*/
				/* out: control block, or NULL */
	buf_page_t*	bpage)	/* in: control block, or NULL */
	__attribute__((pure));
#ifdef UNIV_DEBUG
/*************************************************************************
Gets a pointer to the memory frame of a block. */
UNIV_INLINE
buf_frame_t*
buf_block_get_frame(
/*================*/
					/* out: pointer to the frame */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
#else /* UNIV_DEBUG */
# define buf_block_get_frame(block) (block)->frame
#endif /* UNIV_DEBUG */
/*************************************************************************
Gets the space id of a block. */
UNIV_INLINE
ulint
buf_page_get_space(
/*===============*/
					/* out: space id */
	const buf_page_t*	bpage)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the space id of a block. */
UNIV_INLINE
ulint
buf_block_get_space(
/*================*/
					/* out: space id */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the page number of a block. */
UNIV_INLINE
ulint
buf_page_get_page_no(
/*=================*/
					/* out: page number */
	const buf_page_t*	bpage)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the page number of a block. */
UNIV_INLINE
ulint
buf_block_get_page_no(
/*==================*/
					/* out: page number */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the compressed page size of a block. */
UNIV_INLINE
ulint
buf_page_get_zip_size(
/*==================*/
					/* out: compressed page size, or 0 */
	const buf_page_t*	bpage)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the compressed page size of a block. */
UNIV_INLINE
ulint
buf_block_get_zip_size(
/*===================*/
					/* out: compressed page size, or 0 */
	const buf_block_t*	block)	/* in: pointer to the control block */
	__attribute__((pure));
/*************************************************************************
Gets the compressed page descriptor corresponding to an uncompressed page
if applicable. */
#define buf_block_get_page_zip(block) \
	(UNIV_LIKELY_NULL((block)->page.zip.data) ? &(block)->page.zip : NULL)
/***********************************************************************
Gets the block to whose frame the pointer is pointing to. */
UNIV_INTERN
buf_block_t*
buf_block_align(
/*============*/
				/* out: pointer to block, never NULL */
	const byte*	ptr);	/* in: pointer to a frame */
#if defined UNIV_DEBUG || defined UNIV_ZIP_DEBUG
/*************************************************************************
Gets the compressed page descriptor corresponding to an uncompressed page
if applicable. */
UNIV_INLINE
const page_zip_des_t*
buf_frame_get_page_zip(
/*===================*/
				/* out: compressed page descriptor, or NULL */
	const byte*	ptr);	/* in: pointer to the page */
#endif /* UNIV_DEBUG || UNIV_ZIP_DEBUG */
/************************************************************************
This function is used to get info if there is an io operation
going on on a buffer page. */
UNIV_INLINE
ibool
buf_page_io_query(
/*==============*/
				/* out: TRUE if io going on */
	buf_page_t*	bpage);	/* in: pool block, must be bufferfixed */
/************************************************************************
Function which inits a page for read to the buffer buf_pool. If the page is
(1) already in buf_pool, or
(2) if we specify to read only ibuf pages and the page is not an ibuf page, or
(3) if the space is deleted or being deleted,
then this function does nothing.
Sets the io_fix flag to BUF_IO_READ and sets a non-recursive exclusive lock
on the buffer frame. The io-handler must take care that the flag is cleared
and the lock released later. */
UNIV_INTERN
buf_page_t*
buf_page_init_for_read(
/*===================*/
				/* out: pointer to the block or NULL */
	ulint*		err,	/* out: DB_SUCCESS or DB_TABLESPACE_DELETED */
	ulint		mode,	/* in: BUF_READ_IBUF_PAGES_ONLY, ... */
	ulint		space,	/* in: space id */
	ulint		zip_size,/* in: compressed page size, or 0 */
	ibool		unzip,	/* in: TRUE=request uncompressed page */
	ib_int64_t	tablespace_version,/* in: prevents reading from a wrong
				version of the tablespace in case we have done
				DISCARD + IMPORT */
	ulint		offset);/* in: page number */
/************************************************************************
Completes an asynchronous read or write request of a file page to or from
the buffer pool. */
UNIV_INTERN
void
buf_page_io_complete(
/*=================*/
	buf_page_t*	bpage);	/* in: pointer to the block in question */
/************************************************************************
Calculates a folded value of a file page address to use in the page hash
table. */
UNIV_INLINE
ulint
buf_page_address_fold(
/*==================*/
			/* out: the folded value */
	ulint	space,	/* in: space id */
	ulint	offset)	/* in: offset of the page within space */
	__attribute__((const));
/**********************************************************************
Returns the control block of a file page, NULL if not found. */
UNIV_INLINE
buf_page_t*
buf_page_hash_get(
/*==============*/
			/* out: block, NULL if not found */
	ulint	space,	/* in: space id */
	ulint	offset);/* in: offset of the page within space */
/**********************************************************************
Returns the control block of a file page, NULL if not found
or an uncompressed page frame does not exist. */
UNIV_INLINE
buf_block_t*
buf_block_hash_get(
/*===============*/
			/* out: block, NULL if not found */
	ulint	space,	/* in: space id */
	ulint	offset);/* in: offset of the page within space */
/***********************************************************************
Increments the pool clock by one and returns its new value. Remember that
in the 32 bit version the clock wraps around at 4 billion! */
UNIV_INLINE
ulint
buf_pool_clock_tic(void);
/*====================*/
			/* out: new clock value */
/*************************************************************************
Gets the current length of the free list of buffer blocks. */
UNIV_INTERN
ulint
buf_get_free_list_len(void);
/*=======================*/
/********************************************************************
Stop watching if the marked page is read in. */
UNIV_INTERN
void
buf_pool_watch_clear(void);
/*======================*/
/************************************************************************
Set watch occurred flag. */
UNIV_INTERN
void
buf_pool_watch_notify(
/*==================*/
	ulint	space,	/* in: space id of page read in */
	ulint	offset);/* in: offset of page read in */
/********************************************************************
Check if the given page is being watched and has been read to the buffer
pool. */
UNIV_INTERN
ibool
buf_pool_watch_occurred(
/*====================*/
				/* out: TRUE if the given page is being
				watched and it has been read in */
	ulint	space,		/* in: space id */
	ulint	page_no);	/* in: page number */

/* The common buffer control block structure
for compressed and uncompressed frames */

struct buf_page_struct{
	/* None of the following bit-fields must be modified without
	holding buf_page_get_mutex() [block->mutex or buf_pool_zip_mutex],
	since they can be stored in the same machine word.  Some of them are
	additionally protected by buf_pool_mutex. */

	unsigned	space:32;	/* tablespace id; also protected
					by buf_pool_mutex. */
	unsigned	offset:32;	/* page number; also protected
					by buf_pool_mutex. */

	unsigned	state:3;	/* state of the control block
					(@see enum buf_page_state); also
					protected by buf_pool_mutex.
					State transitions from
					BUF_BLOCK_READY_FOR_USE to
					BUF_BLOCK_MEMORY need not be
					protected by buf_page_get_mutex(). */
	unsigned	flush_type:2;	/* if this block is currently being
					flushed to disk, this tells the
					flush_type (@see enum buf_flush) */
	unsigned	accessed:1;	/* TRUE if the page has been accessed
					while in the buffer pool: read-ahead
					may read in pages which have not been
					accessed yet; a thread is allowed to
					read this for heuristic purposes
					without holding any mutex or latch */
	unsigned	io_fix:2;	/* type of pending I/O operation
					(@see enum buf_io_fix); also
					protected by buf_pool_mutex */
	unsigned	buf_fix_count:24;/* count of how manyfold this block
					is currently bufferfixed */

	page_zip_des_t	zip;		/* compressed page; zip.data
					(but not the data it points to) is
					also protected by buf_pool_mutex */
	buf_page_t*	hash;		/* node used in chaining to
					buf_pool->page_hash or
					buf_pool->zip_hash */
#ifdef UNIV_DEBUG
	ibool		in_page_hash;	/* TRUE if in buf_pool->page_hash */
	ibool		in_zip_hash;	/* TRUE if in buf_pool->zip_hash */
#endif /* UNIV_DEBUG */

	/* 2. Page flushing fields; protected by buf_pool_mutex */

	UT_LIST_NODE_T(buf_page_t) list;
					/* based on state, this is a list
					node in one of the following lists
					in buf_pool:

					BUF_BLOCK_NOT_USED:	free
					BUF_BLOCK_FILE_PAGE:	flush_list
					BUF_BLOCK_ZIP_DIRTY:	flush_list
					BUF_BLOCK_ZIP_PAGE:	zip_clean
					BUF_BLOCK_ZIP_FREE:	zip_free[] */
#ifdef UNIV_DEBUG
	ibool		in_flush_list;	/* TRUE if in buf_pool->flush_list;
					when buf_pool_mutex is free, the
					following should hold: in_flush_list
					== (state == BUF_BLOCK_FILE_PAGE
					    || state == BUF_BLOCK_ZIP_DIRTY) */
	ibool		in_free_list;	/* TRUE if in buf_pool->free; when
					buf_pool_mutex is free, the following
					should hold: in_free_list
					== (state == BUF_BLOCK_NOT_USED) */
#endif /* UNIV_DEBUG */
	ib_uint64_t	newest_modification;
					/* log sequence number of the youngest
					modification to this block, zero if
					not modified */
	ib_uint64_t	oldest_modification;
					/* log sequence number of the START of
					the log entry written of the oldest
					modification to this block which has
					not yet been flushed on disk; zero if
					all modifications are on disk */

	/* 3. LRU replacement algorithm fields; protected by
	buf_pool_mutex only (not buf_pool_zip_mutex or block->mutex) */

	UT_LIST_NODE_T(buf_page_t) LRU;
					/* node of the LRU list */
#ifdef UNIV_DEBUG
	ibool		in_LRU_list;	/* TRUE if the page is in the LRU list;
					used in debugging */
#endif /* UNIV_DEBUG */
	unsigned	old:1;		/* TRUE if the block is in the old
					blocks in the LRU list */
	unsigned	LRU_position:31;/* value which monotonically decreases
					(or may stay constant if old==TRUE)
					toward the end of the LRU list, if
					buf_pool->ulint_clock has not wrapped
					around: NOTE that this value can only
					be used in heuristic algorithms,
					because of the possibility of a
					wrap-around! */
	unsigned	freed_page_clock:32;/* the value of
					buf_pool->freed_page_clock when this
					block was the last time put to the
					head of the LRU list; a thread is
					allowed to read this for heuristic
					purposes without holding any mutex or
					latch */
#ifdef UNIV_DEBUG_FILE_ACCESSES
	ibool		file_page_was_freed;
					/* this is set to TRUE when fsp
					frees a page in buffer pool */
#endif /* UNIV_DEBUG_FILE_ACCESSES */
};

/* The buffer control block structure */

struct buf_block_struct{

	/* 1. General fields */

	buf_page_t	page;		/* page information; this must
					be the first field, so that
					buf_pool->page_hash can point
					to buf_page_t or buf_block_t */
	UT_LIST_NODE_T(buf_block_t) unzip_LRU;
					/* node of the decompressed LRU list;
					a block is in the unzip_LRU list
					if page.state == BUF_BLOCK_FILE_PAGE
					and page.zip.data != NULL */
#ifdef UNIV_DEBUG
	ibool		in_unzip_LRU_list;/* TRUE if the page is in the
					decompressed LRU list;
					used in debugging */
#endif /* UNIV_DEBUG */
	byte*		frame;		/* pointer to buffer frame which
					is of size UNIV_PAGE_SIZE, and
					aligned to an address divisible by
					UNIV_PAGE_SIZE */
	mutex_t		mutex;		/* mutex protecting this block:
					state (also protected by the buffer
					pool mutex), io_fix, buf_fix_count,
					and accessed; we introduce this new
					mutex in InnoDB-5.1 to relieve
					contention on the buffer pool mutex */
	rw_lock_t	lock;		/* read-write lock of the buffer
					frame */
	unsigned	lock_hash_val:32;/* hashed value of the page address
					in the record lock hash table */
	unsigned	check_index_page_at_flush:1;
					/* TRUE if we know that this is
					an index page, and want the database
					to check its consistency before flush;
					note that there may be pages in the
					buffer pool which are index pages,
					but this flag is not set because
					we do not keep track of all pages */

	/* 2. Optimistic search field */

	ib_uint64_t	modify_clock;	/* this clock is incremented every
					time a pointer to a record on the
					page may become obsolete; this is
					used in the optimistic cursor
					positioning: if the modify clock has
					not changed, we know that the pointer
					is still valid; this field may be
					changed if the thread (1) owns the
					pool mutex and the page is not
					bufferfixed, or (2) the thread has an
					x-latch on the block */

	/* 3. Hash search fields: NOTE that the first 4 fields are NOT
	protected by any semaphore! */

	ulint		n_hash_helps;	/* counter which controls building
					of a new hash index for the page */
	ulint		n_fields;	/* recommended prefix length for hash
					search: number of full fields */
	ulint		n_bytes;	/* recommended prefix: number of bytes
					in an incomplete field */
	ibool		left_side;	/* TRUE or FALSE, depending on
					whether the leftmost record of several
					records with the same prefix should be
					indexed in the hash index */

	/* These 6 fields may only be modified when we have
	an x-latch on btr_search_latch AND
	a) we are holding an s-latch or x-latch on block->lock or
	b) we know that block->buf_fix_count == 0.

	An exception to this is when we init or create a page
	in the buffer pool in buf0buf.c. */

#if defined UNIV_AHI_DEBUG || defined UNIV_DEBUG
	ulint		n_pointers;	/* used in debugging: the number of
					pointers in the adaptive hash index
					pointing to this frame */
#endif /* UNIV_AHI_DEBUG || UNIV_DEBUG */
	unsigned	is_hashed:1;	/* TRUE if hash index has already been
					built on this page; note that it does
					not guarantee that the index is
					complete, though: there may have been
					hash collisions, record deletions,
					etc. */
	unsigned	curr_n_fields:10;/* prefix length for hash indexing:
					number of full fields */
	unsigned	curr_n_bytes:15;/* number of bytes in hash indexing */
	unsigned	curr_left_side:1;/* TRUE or FALSE in hash indexing */
	dict_index_t*	index;		/* Index for which the adaptive
					hash index has been created. */
	/* 4. Debug fields */
#ifdef UNIV_SYNC_DEBUG
	rw_lock_t	debug_latch;	/* in the debug version, each thread
					which bufferfixes the block acquires
					an s-latch here; so we can use the
					debug utilities in sync0rw */
#endif
};

/* Check if a buf_block_t object is in a valid state. */
#define buf_block_state_valid(block)				\
(buf_block_get_state(block) >= BUF_BLOCK_NOT_USED		\
 && (buf_block_get_state(block) <= BUF_BLOCK_REMOVE_HASH))

/**************************************************************************
Compute the hash fold value for blocks in buf_pool->zip_hash. */
#define BUF_POOL_ZIP_FOLD_PTR(ptr) ((ulint) (ptr) / UNIV_PAGE_SIZE)
#define BUF_POOL_ZIP_FOLD(b) BUF_POOL_ZIP_FOLD_PTR((b)->frame)
#define BUF_POOL_ZIP_FOLD_BPAGE(b) BUF_POOL_ZIP_FOLD((buf_block_t*) (b))

/* The buffer pool structure. NOTE! The definition appears here only for
other modules of this directory (buf) to see it. Do not use from outside! */

struct buf_pool_struct{

	/* 1. General fields */

	ulint		n_chunks;	/* number of buffer pool chunks */
	buf_chunk_t*	chunks;		/* buffer pool chunks */
	ulint		curr_size;	/* current pool size in pages */
	hash_table_t*	page_hash;	/* hash table of buf_page_t or
					buf_block_t file pages,
					buf_page_in_file() == TRUE,
					indexed by (space_id, offset) */
	/*--------------------------*/	/* Delete buffering data */
	ibool		watch_active;	/* if TRUE, set watch_occurred
					when watch_space, watch_page_no
					is read in. */
	ulint		watch_space;	/* space id of watched page */
	ulint		watch_page_no;	/* page number of watched page */
	ibool		watch_occurred;	/* has watched page been read in */
	/*--------------------------*/


	hash_table_t*	zip_hash;	/* hash table of buf_block_t blocks
					whose frames are allocated to the
					zip buddy system,
					indexed by block->frame */
	ulint		n_pend_reads;	/* number of pending read operations */
	ulint		n_pend_unzip;	/* number of pending decompressions */

	time_t		last_printout_time; /* when buf_print was last time
					called */
	ulint		n_pages_read;	/* number read operations */
	ulint		n_pages_written;/* number write operations */
	ulint		n_pages_created;/* number of pages created in the pool
					with no read */
	ulint		n_page_gets;	/* number of page gets performed;
					also successful searches through
					the adaptive hash index are
					counted as page gets; this field
					is NOT protected by the buffer
					pool mutex */
	ulint		n_page_gets_old;/* n_page_gets when buf_print was
					last time called: used to calculate
					hit rate */
	ulint		n_pages_read_old;/* n_pages_read when buf_print was
					last time called */
	ulint		n_pages_written_old;/* number write operations */
	ulint		n_pages_created_old;/* number of pages created in
					the pool with no read */
	/* 2. Page flushing algorithm fields */

	UT_LIST_BASE_NODE_T(buf_page_t) flush_list;
					/* base node of the modified block
					list */
	ibool		init_flush[BUF_FLUSH_N_TYPES];
					/* this is TRUE when a flush of the
					given type is being initialized */
	ulint		n_flush[BUF_FLUSH_N_TYPES];
					/* this is the number of pending
					writes in the given flush type */
	os_event_t	no_flush[BUF_FLUSH_N_TYPES];
					/* this is in the set state when there
					is no flush batch of the given type
					running */
	ib_rbt_t*	flush_rbt;	/* a red-black tree is used
					exclusively during recovery to
					speed up insertions in the
					flush_list. This tree contains
					blocks in order of
					oldest_modification LSN and is
					kept in sync with the
					flush_list.
					Each member of the tree MUST
					also be on the flush_list.
					This tree is relevant only in
					recovery and is set to NULL
					once the recovery is over. */
	ulint		ulint_clock;	/* a sequence number used to count
					time. NOTE! This counter wraps
					around at 4 billion (if ulint ==
					32 bits)! */
	ulint		freed_page_clock;/* a sequence number used to count the
					number of buffer blocks removed from
					the end of the LRU list; NOTE that
					this counter may wrap around at 4
					billion! A thread is allowed to
					read this for heuristic purposes
					without holding any mutex or latch */
	ulint		LRU_flush_ended;/* when an LRU flush ends for a page,
					this is incremented by one; this is
					set to zero when a buffer block is
					allocated */

	/* 3. LRU replacement algorithm fields */

	UT_LIST_BASE_NODE_T(buf_page_t) free;
					/* base node of the free block list */
	UT_LIST_BASE_NODE_T(buf_page_t) LRU;
					/* base node of the LRU list */
	buf_page_t*	LRU_old;	/* pointer to the about 3/8 oldest
					blocks in the LRU list; NULL if LRU
					length less than BUF_LRU_OLD_MIN_LEN;
					NOTE: when LRU_old != NULL, its length
					should always equal LRU_old_len */
	ulint		LRU_old_len;	/* length of the LRU list from
					the block to which LRU_old points
					onward, including that block;
					see buf0lru.c for the restrictions
					on this value; not defined if
					LRU_old == NULL;
					NOTE: LRU_old_len must be adjusted
					whenever LRU_old shrinks or grows! */

	UT_LIST_BASE_NODE_T(buf_block_t) unzip_LRU;
					/* base node of the unzip_LRU list */

	/* 4. Fields for the buddy allocator of compressed pages */
	UT_LIST_BASE_NODE_T(buf_page_t)	zip_clean;
					/* unmodified compressed pages */
	UT_LIST_BASE_NODE_T(buf_page_t) zip_free[BUF_BUDDY_SIZES];
					/* buddy free lists */
#if BUF_BUDDY_HIGH != UNIV_PAGE_SIZE
# error "BUF_BUDDY_HIGH != UNIV_PAGE_SIZE"
#endif
#if BUF_BUDDY_LOW > PAGE_ZIP_MIN_SIZE
# error "BUF_BUDDY_LOW > PAGE_ZIP_MIN_SIZE"
#endif
};

/* mutex protecting the buffer pool struct and control blocks, except the
read-write lock in them */
extern mutex_t	buf_pool_mutex;
/* mutex protecting the control blocks of compressed-only pages
(of type buf_page_t, not buf_block_t) */
extern mutex_t	buf_pool_zip_mutex;

/* Accessors for buf_pool_mutex.  Use these instead of accessing
buf_pool_mutex directly. */

/* Test if buf_pool_mutex is owned. */
#define buf_pool_mutex_own() mutex_own(&buf_pool_mutex)
/* Acquire the buffer pool mutex. */
#define buf_pool_mutex_enter() do {		\
	ut_ad(!mutex_own(&buf_pool_zip_mutex));	\
	mutex_enter(&buf_pool_mutex);		\
} while (0)

#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/** Flag to forbid the release of the buffer pool mutex.
Protected by buf_pool_mutex. */
extern ulint	buf_pool_mutex_exit_forbidden;
/* Forbid the release of the buffer pool mutex. */
# define buf_pool_mutex_exit_forbid() do {	\
	ut_ad(buf_pool_mutex_own());		\
	buf_pool_mutex_exit_forbidden++;	\
} while (0)
/* Allow the release of the buffer pool mutex. */
# define buf_pool_mutex_exit_allow() do {	\
	ut_ad(buf_pool_mutex_own());		\
	ut_a(buf_pool_mutex_exit_forbidden);	\
	buf_pool_mutex_exit_forbidden--;	\
} while (0)
/* Release the buffer pool mutex. */
# define buf_pool_mutex_exit() do {		\
	ut_a(!buf_pool_mutex_exit_forbidden);	\
	mutex_exit(&buf_pool_mutex);		\
} while (0)
#else
/* Forbid the release of the buffer pool mutex. */
# define buf_pool_mutex_exit_forbid() ((void) 0)
/* Allow the release of the buffer pool mutex. */
# define buf_pool_mutex_exit_allow() ((void) 0)
/* Release the buffer pool mutex. */
# define buf_pool_mutex_exit() mutex_exit(&buf_pool_mutex)
#endif

/************************************************************************
Let us list the consistency conditions for different control block states.

NOT_USED:	is in free list, not in LRU list, not in flush list, nor
		page hash table
READY_FOR_USE:	is not in free list, LRU list, or flush list, nor page
		hash table
MEMORY:		is not in free list, LRU list, or flush list, nor page
		hash table
FILE_PAGE:	space and offset are defined, is in page hash table
		if io_fix == BUF_IO_WRITE,
			pool: no_flush[flush_type] is in reset state,
			pool: n_flush[flush_type] > 0

		(1) if buf_fix_count == 0, then
			is in LRU list, not in free list
			is in flush list,
				if and only if oldest_modification > 0
			is x-locked,
				if and only if io_fix == BUF_IO_READ
			is s-locked,
				if and only if io_fix == BUF_IO_WRITE

		(2) if buf_fix_count > 0, then
			is not in LRU list, not in free list
			is in flush list,
				if and only if oldest_modification > 0
			if io_fix == BUF_IO_READ,
				is x-locked
			if io_fix == BUF_IO_WRITE,
				is s-locked

State transitions:

NOT_USED => READY_FOR_USE
READY_FOR_USE => MEMORY
READY_FOR_USE => FILE_PAGE
MEMORY => NOT_USED
FILE_PAGE => NOT_USED	NOTE: This transition is allowed if and only if
				(1) buf_fix_count == 0,
				(2) oldest_modification == 0, and
				(3) io_fix == 0.
*/

#ifndef UNIV_NONINL
#include "buf0buf.ic"
#endif

#endif