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/**************************************************//**
@file include/buf0rea.h
The database buffer read

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

#ifndef buf0rea_h
#define buf0rea_h

#include "univ.i"
#include "buf0buf.h"
#include "buf0types.h"

/** High-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there. Sets the io_fix flag and sets
an exclusive lock on the buffer frame. The flag is cleared and the x-lock
released by the i/o-handler thread.
@param[in]	page_id		page id
@param[in]	page_size	page size
@return TRUE if page has been read in, FALSE in case of failure */
ibool
buf_read_page(
	const page_id_t&	page_id,
	const page_size_t&	page_size);

/** High-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there. Sets the io_fix flag and sets
an exclusive lock on the buffer frame. The flag is cleared and the x-lock
released by the i/o-handler thread.
@param[in]	page_id		page id
@param[in]	page_size	page size
@param[in]	sync		true if synchronous aio is desired
@return TRUE if page has been read in, FALSE in case of failure */
ibool
buf_read_page_background(
	const page_id_t&	page_id,
	const page_size_t&	page_size,
	bool			sync);

/** Applies a random read-ahead in buf_pool if there are at least a threshold
value of accessed pages from the random read-ahead area. Does not read any
page, not even the one at the position (space, offset), if the read-ahead
mechanism is not activated. NOTE 1: the calling thread may own latches on
pages: to avoid deadlocks this function must be written such that it cannot
end up waiting for these latches! NOTE 2: the calling thread must want
access to the page given: this rule is set to prevent unintended read-aheads
performed by ibuf routines, a situation which could result in a deadlock if
the OS does not support asynchronous i/o.
@param[in]	page_id		page id of a page which the current thread
wants to access
@param[in]	page_size	page size
@param[in]	inside_ibuf	TRUE if we are inside ibuf routine
@return number of page read requests issued; NOTE that if we read ibuf
pages, it may happen that the page at the given page number does not
get read even if we return a positive value! */
ulint
buf_read_ahead_random(
	const page_id_t&	page_id,
	const page_size_t&	page_size,
	ibool			inside_ibuf);

/** Applies linear read-ahead if in the buf_pool the page is a border page of
a linear read-ahead area and all the pages in the area have been accessed.
Does not read any page if the read-ahead mechanism is not activated. Note
that the algorithm looks at the 'natural' adjacent successor and
predecessor of the page, which on the leaf level of a B-tree are the next
and previous page in the chain of leaves. To know these, the page specified
in (space, offset) must already be present in the buf_pool. Thus, the
natural way to use this function is to call it when a page in the buf_pool
is accessed the first time, calling this function just after it has been
bufferfixed.
NOTE 1: as this function looks at the natural predecessor and successor
fields on the page, what happens, if these are not initialized to any
sensible value? No problem, before applying read-ahead we check that the
area to read is within the span of the space, if not, read-ahead is not
applied. An uninitialized value may result in a useless read operation, but
only very improbably.
NOTE 2: the calling thread may own latches on pages: to avoid deadlocks this
function must be written such that it cannot end up waiting for these
latches!
NOTE 3: the calling thread must want access to the page given: this rule is
set to prevent unintended read-aheads performed by ibuf routines, a situation
which could result in a deadlock if the OS does not support asynchronous io.
@param[in]	page_id		page id; see NOTE 3 above
@param[in]	page_size	page size
@param[in]	inside_ibuf	TRUE if we are inside ibuf routine
@return number of page read requests issued */
ulint
buf_read_ahead_linear(
	const page_id_t&	page_id,
	const page_size_t&	page_size,
	ibool			inside_ibuf);

/********************************************************************//**
Issues read requests for pages which the ibuf module wants to read in, in
order to contract the insert buffer tree. Technically, this function is like
a read-ahead function. */
void
buf_read_ibuf_merge_pages(
/*======================*/
	bool		sync,		/*!< in: true if the caller
					wants this function to wait
					for the highest address page
					to get read in, before this
					function returns */
	const ulint*	space_ids,	/*!< in: array of space ids */
	const ulint*	page_nos,	/*!< in: array of page numbers
					to read, with the highest page
					number the last in the
					array */
	ulint		n_stored);	/*!< in: number of elements
					in the arrays */

/** Issues read requests for pages which recovery wants to read in.
@param[in]	sync		true if the caller wants this function to wait
for the highest address page to get read in, before this function returns
@param[in]	space_id	tablespace id
@param[in]	page_nos	array of page numbers to read, with the
highest page number the last in the array
@param[in]	n_stored	number of page numbers in the array */

void
buf_read_recv_pages(
	bool		sync,
	ulint		space_id,
	const ulint*	page_nos,
	ulint		n_stored);

/** The size in pages of the area which the read-ahead algorithms read if
invoked */
#define	BUF_READ_AHEAD_AREA(b)		((b)->read_ahead_area)

/** @name Modes used in read-ahead @{ */
/** read only pages belonging to the insert buffer tree */
#define BUF_READ_IBUF_PAGES_ONLY	131
/** read any page */
#define BUF_READ_ANY_PAGE		132
/* @} */

#endif
