~drizzle-trunk/drizzle/development

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

The database buffer read

(c) 1995 Innobase Oy

Created 11/5/1995 Heikki Tuuri

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

#ifndef buf0rea_h

#define buf0rea_h

#include "univ.i"

#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. Does a random read-ahead if it seems

sensible. */

ulint

buf_read_page(

/*==========*/

			/* out: number of page read requests issued: this can

			be > 1 if read-ahead occurred */

	ulint	space,	/* in: space id */

	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. */

ulint

buf_read_ahead_linear(

/*==================*/

			/* out: number of page read requests issued */

	ulint	space,	/* in: space id */

	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. */

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 */

	ulint*	space_ids,	/* in: array of space ids */

	ib_longlong* 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 */

	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 */

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

Issues read requests for pages which recovery wants to read in. */

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*	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					\

	ut_min(64, ut_2_power_up(buf_pool->curr_size / 32))

/* Modes used in read-ahead */

#define BUF_READ_IBUF_PAGES_ONLY	131

#define BUF_READ_ANY_PAGE		132

#endif