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

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

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

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

#pragma once
#ifndef buf0rea_h
#define buf0rea_h

#include "univ.i"
#include "buf0types.h"
#include "trx0types.h"

/********************************************************************//**
Low-level function which reads a page asynchronously from a file to the
buffer buf_pool if it is not already there, in which case does nothing.
Sets the io_fix flag and sets an exclusive lock on the buffer frame. The
flag is cleared and the x-lock released by an i/o-handler thread.
@return 1 if a read request was queued, 0 if the page already resided
in buf_pool, or if the page is in the doublewrite buffer blocks in
which case it is never read into the pool, or if the tablespace does
not exist or is being dropped TODO update
@return 1 if read request is issued. 0 if it is not */
UNIV_INTERN
ulint
buf_read_page_low(
/*==============*/
	ulint*	err,	/*!< out: DB_SUCCESS or DB_TABLESPACE_DELETED if we are
			trying to read from a non-existent tablespace, or a
			tablespace which is just now being dropped */
	ibool	sync,	/*!< in: true if synchronous aio is desired */
	ulint	mode,	/*!< in: BUF_READ_IBUF_PAGES_ONLY, ...,
			ORed to OS_AIO_SIMULATED_WAKE_LATER (see below
			at read-ahead functions) */
	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: if the space memory object has
				       this timestamp different from what we are giving here,
				       treat the tablespace as dropped; this is a timestamp we
				       use to stop dangling page reads from a tablespace
				       which we have DISCARDed + IMPORTed back */
	ulint	offset);/*!< in: page number */

/********************************************************************//**
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.
@return TRUE if page has been read in, FALSE in case of failure */
UNIV_INTERN
ibool
buf_read_page(
/*==========*/
	ulint	space,	/*!< in: space id */
	ulint	zip_size,/*!< in: compressed page size in bytes, or 0 */
	ulint	offset);/*!< in: page number */
/********************************************************************//**
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 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.
@return	number of page read requests issued */
UNIV_INTERN
ulint
buf_read_ahead_linear(
/*==================*/
	ulint	space,	/*!< in: space id */
	ulint	zip_size,/*!< in: compressed page size in bytes, or 0 */
	ulint	offset);/*!< in: page number of a page; NOTE: the current thread
			must want access to this page (see NOTE 3 above) */
/********************************************************************//**
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. */
UNIV_INTERN
void
buf_read_ibuf_merge_pages(
/*======================*/
	ibool		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 ib_int64_t* space_versions,/*!< in: the spaces must have
					this version number
					(timestamp), otherwise we
					discard the read; we use this
					to cancel reads if DISCARD +
					IMPORT may have changed the
					tablespace size */
	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. */
UNIV_INTERN
void
buf_read_recv_pages(
/*================*/
	ibool		sync,		/*!< in: TRUE if the caller
					wants this function to wait
					for the highest address page
					to get read in, before this
					function returns */
	ulint		space,		/*!< in: space id */
	ulint		zip_size,	/*!< in: compressed page size in
					bytes, or 0 */
	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 page numbers
					in the array */

/** The size in pages of the area which the read-ahead algorithms read if
invoked */
#define	BUF_READ_AHEAD_AREA(b)		64

/** @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