/*****************************************************************************

Copyright (C) 1995, 2009, Innobase Oy. All Rights Reserved.

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

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 along with
this program; if not, write to the Free Software Foundation, Inc., 51 Franklin
St, Fifth Floor, Boston, MA 02110-1301 USA

*****************************************************************************/

/**************************************************//**
@file include/buf0lru.h
The database buffer pool LRU replacement algorithm

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

#ifndef buf0lru_h
#define buf0lru_h

#include <sys/types.h>
#include "univ.i"
#include "ut0byte.h"
#include "buf0types.h"

/** The return type of buf_LRU_free_block() */
enum buf_lru_free_block_status {
	/** freed */
	BUF_LRU_FREED = 0,
	/** not freed because the caller asked to remove the
	uncompressed frame but the control block cannot be
	relocated */
	BUF_LRU_CANNOT_RELOCATE,
	/** not freed because of some other reason */
	BUF_LRU_NOT_FREED
};

/******************************************************************//**
Tries to remove LRU flushed blocks from the end of the LRU list and put them
to the free list. This is beneficial for the efficiency of the insert buffer
operation, as flushed pages from non-unique non-clustered indexes are here
taken out of the buffer pool, and their inserts redirected to the insert
buffer. Otherwise, the flushed blocks could get modified again before read
operations need new buffer blocks, and the i/o work done in flushing would be
wasted. */
UNIV_INTERN
void
buf_LRU_try_free_flushed_blocks(
/*============================*/
	buf_pool_t*	buf_pool);	/*!< in: buffer pool instance */
/******************************************************************//**
Returns TRUE if less than 25 % of the buffer pool is available. This can be
used in heuristics to prevent huge transactions eating up the whole buffer
pool for their locks.
@return	TRUE if less than 25 % of buffer pool left */
UNIV_INTERN
ibool
buf_LRU_buf_pool_running_out(void);
/*==============================*/

/*#######################################################################
These are low-level functions
#########################################################################*/

/** Minimum LRU list length for which the LRU_old pointer is defined */
#define BUF_LRU_OLD_MIN_LEN	512	/* 8 megabytes of 16k pages */

/** Maximum LRU list search length in buf_flush_LRU_recommendation() */
#define BUF_LRU_FREE_SEARCH_LEN(b)	(5 + 2 * BUF_READ_AHEAD_AREA(b))

/******************************************************************//**
Invalidates all pages belonging to a given tablespace when we are deleting
the data file(s) of that tablespace. A PROBLEM: if readahead is being started,
what guarantees that it will not try to read in pages after this operation has
completed? */
UNIV_INTERN
void
buf_LRU_invalidate_tablespace(
/*==========================*/
	ulint	id);	/*!< in: space id */
/********************************************************************//**
Insert a compressed block into buf_pool->zip_clean in the LRU order. */
UNIV_INTERN
void
buf_LRU_insert_zip_clean(
/*=====================*/
	buf_page_t*	bpage);	/*!< in: pointer to the block in question */

/******************************************************************//**
Try to free a block.  If bpage is a descriptor of a compressed-only
page, the descriptor object will be freed as well.

NOTE: If this function returns BUF_LRU_FREED, it will temporarily
release buf_pool->mutex.  Furthermore, the page frame will no longer be
accessible via bpage.

The caller must hold buf_pool->mutex and buf_page_get_mutex(bpage) and
release these two mutexes after the call.  No other
buf_page_get_mutex() may be held when calling this function.
@return BUF_LRU_FREED if freed, BUF_LRU_CANNOT_RELOCATE or
BUF_LRU_NOT_FREED otherwise. */
UNIV_INTERN
enum buf_lru_free_block_status
buf_LRU_free_block(
/*===============*/
	buf_page_t*	bpage,	/*!< in: block to be freed */
	ibool		zip,	/*!< in: TRUE if should remove also the
				compressed page of an uncompressed page */
	ibool*		buf_pool_mutex_released);
				/*!< in: pointer to a variable that will
				be assigned TRUE if buf_pool->mutex
				was temporarily released, or NULL */
/******************************************************************//**
Try to free a replaceable block.
@return	TRUE if found and freed */
UNIV_INTERN
ibool
buf_LRU_search_and_free_block(
/*==========================*/
	buf_pool_t*	buf_pool,	/*!< in: buffer pool instance */
	ulint		n_iterations);	/*!< in: how many times this has
					been called repeatedly without
					result: a high value means that
					we should search farther; if
					n_iterations < 10, then we search
					n_iterations / 10 * buf_pool->curr_size
					pages from the end of the LRU list; if
					n_iterations < 5, then we will
					also search n_iterations / 5
					of the unzip_LRU list. */
/******************************************************************//**
Returns a free block from the buf_pool.  The block is taken off the
free list.  If it is empty, returns NULL.
@return	a free control block, or NULL if the buf_block->free list is empty */
UNIV_INTERN
buf_block_t*
buf_LRU_get_free_only(
/*==================*/
	buf_pool_t*	buf_pool);	/*!< buffer pool instance */
/******************************************************************//**
Returns a free block from the buf_pool. The block is taken off the
free list. If it is empty, blocks are moved from the end of the
LRU list to the free list.
@return	the free control block, in state BUF_BLOCK_READY_FOR_USE */
UNIV_INTERN
buf_block_t*
buf_LRU_get_free_block(
/*===================*/
	buf_pool_t*	buf_pool,	/*!< in: preferred buffer pool */
	ulint		zip_size);	/*!< in: compressed page size in bytes,
					or 0 if uncompressed tablespace */

/******************************************************************//**
Puts a block back to the free list. */
UNIV_INTERN
void
buf_LRU_block_free_non_file_page(
/*=============================*/
	buf_block_t*	block);	/*!< in: block, must not contain a file page */
/******************************************************************//**
Adds a block to the LRU list. */
UNIV_INTERN
void
buf_LRU_add_block(
/*==============*/
	buf_page_t*	bpage,	/*!< in: control block */
	ibool		old);	/*!< in: TRUE if should be put to the old
				blocks in the LRU list, else put to the
				start; if the LRU list is very short, added to
				the start regardless of this parameter */
/******************************************************************//**
Adds a block to the LRU list of decompressed zip pages. */
UNIV_INTERN
void
buf_unzip_LRU_add_block(
/*====================*/
	buf_block_t*	block,	/*!< in: control block */
	ibool		old);	/*!< in: TRUE if should be put to the end
				of the list, else put to the start */
/******************************************************************//**
Moves a block to the start of the LRU list. */
UNIV_INTERN
void
buf_LRU_make_block_young(
/*=====================*/
	buf_page_t*	bpage);	/*!< in: control block */
/******************************************************************//**
Moves a block to the end of the LRU list. */
UNIV_INTERN
void
buf_LRU_make_block_old(
/*===================*/
	buf_page_t*	bpage);	/*!< in: control block */
/**********************************************************************//**
Updates buf_LRU_old_ratio.
@return	updated old_pct */
UNIV_INTERN
ulint
buf_LRU_old_ratio_update(
/*=====================*/
	uint	old_pct,/*!< in: Reserve this percentage of
			the buffer pool for "old" blocks. */
	ibool	adjust);/*!< in: TRUE=adjust the LRU list;
			FALSE=just assign buf_LRU_old_ratio
			during the initialization of InnoDB */
/********************************************************************//**
Update the historical stats that we are collecting for LRU eviction
policy at the end of each interval. */
UNIV_INTERN
void
buf_LRU_stat_update(void);
/*=====================*/

#if defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/**********************************************************************//**
Validates the LRU list.
@return	TRUE */
UNIV_INTERN
ibool
buf_LRU_validate(void);
/*==================*/
#endif /* UNIV_DEBUG || UNIV_BUF_DEBUG */
#if defined UNIV_DEBUG_PRINT || defined UNIV_DEBUG || defined UNIV_BUF_DEBUG
/**********************************************************************//**
Prints the LRU list. */
UNIV_INTERN
void
buf_LRU_print(void);
/*===============*/
#endif /* UNIV_DEBUG_PRINT || UNIV_DEBUG || UNIV_BUF_DEBUG */

/** @name Heuristics for detecting index scan @{ */
/** Reserve this much/BUF_LRU_OLD_RATIO_DIV of the buffer pool for
"old" blocks.  Protected by buf_pool->mutex. */
extern uint	buf_LRU_old_ratio;
/** The denominator of buf_LRU_old_ratio. */
#define BUF_LRU_OLD_RATIO_DIV	1024
/** Maximum value of buf_LRU_old_ratio.
@see buf_LRU_old_adjust_len
@see buf_LRU_old_ratio_update */
#define BUF_LRU_OLD_RATIO_MAX	BUF_LRU_OLD_RATIO_DIV
/** Minimum value of buf_LRU_old_ratio.
@see buf_LRU_old_adjust_len
@see buf_LRU_old_ratio_update
The minimum must exceed
(BUF_LRU_OLD_TOLERANCE + 5) * BUF_LRU_OLD_RATIO_DIV / BUF_LRU_OLD_MIN_LEN. */
#define BUF_LRU_OLD_RATIO_MIN	51

#if BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX
# error "BUF_LRU_OLD_RATIO_MIN >= BUF_LRU_OLD_RATIO_MAX"
#endif
#if BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV
# error "BUF_LRU_OLD_RATIO_MAX > BUF_LRU_OLD_RATIO_DIV"
#endif

/** Move blocks to "new" LRU list only if the first access was at
least this many milliseconds ago.  Not protected by any mutex or latch. */
extern uint	buf_LRU_old_threshold_ms;
/* @} */

/** @brief Statistics for selecting the LRU list for eviction.

These statistics are not 'of' LRU but 'for' LRU.  We keep count of I/O
and page_zip_decompress() operations.  Based on the statistics we decide
if we want to evict from buf_pool->unzip_LRU or buf_pool->LRU. */
struct buf_LRU_stat_struct
{
	ulint	io;	/**< Counter of buffer pool I/O operations. */
	ulint	unzip;	/**< Counter of page_zip_decompress operations. */
};

/** Statistics for selecting the LRU list for eviction. */
typedef struct buf_LRU_stat_struct buf_LRU_stat_t;

/** Current operation counters.  Not protected by any mutex.
Cleared by buf_LRU_stat_update(). */
extern buf_LRU_stat_t	buf_LRU_stat_cur;

/** Running sum of past values of buf_LRU_stat_cur.
Updated by buf_LRU_stat_update().  Protected by buf_pool->mutex. */
extern buf_LRU_stat_t	buf_LRU_stat_sum;

/********************************************************************//**
Increments the I/O counter in buf_LRU_stat_cur. */
#define buf_LRU_stat_inc_io() buf_LRU_stat_cur.io++
/********************************************************************//**
Increments the page_zip_decompress() counter in buf_LRU_stat_cur. */
#define buf_LRU_stat_inc_unzip() buf_LRU_stat_cur.unzip++

#ifndef UNIV_NONINL
#include "buf0lru.ic"
#endif

#endif