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

Include dependency graph for buf0rea.h:

This graph shows which files directly or indirectly include this file:

Macros
#define	BUF_READ_AHEAD_AREA(b) ut_min(64, ut_2_power_up((b)->curr_size / 32))
Modes used in read-ahead @{
#define	BUF_READ_IBUF_PAGES_ONLY 131
#define	BUF_READ_ANY_PAGE 132
#define	BUF_READ_IGNORE_NONEXISTENT_PAGES 1024

Functions
UNIV_INTERN ibool	buf_read_page (ulint space, ulint zip_size, ulint offset)
UNIV_INTERN ibool	buf_read_page_async (ulint space, ulint offset)
UNIV_INTERN ulint	buf_read_ahead_random (ulint space, ulint zip_size, ulint offset, ibool inside_ibuf)
UNIV_INTERN ulint	buf_read_ahead_linear (ulint space, ulint zip_size, ulint offset, ibool inside_ibuf)
UNIV_INTERN void	buf_read_ibuf_merge_pages (bool sync, const ulint space_ids, const ib_int64_t space_versions, const ulint *page_nos, ulint n_stored)
UNIV_INTERN void	buf_read_recv_pages (ibool sync, ulint space, ulint zip_size, const ulint *page_nos, ulint n_stored)

Detailed Description

The database buffer read

Created 11/5/1995 Heikki Tuuri

Macro Definition Documentation

#define BUF_READ_AHEAD_AREA ( b ) ut_min(64, ut_2_power_up((b)->curr_size / 32))

The size in pages of the area which the read-ahead algorithms read if

invoked

#define BUF_READ_ANY_PAGE 132

read any page

#define BUF_READ_IBUF_PAGES_ONLY 131

read only pages belonging to the insert buffer tree

#define BUF_READ_IGNORE_NONEXISTENT_PAGES 1024

read any page, but ignore (return an error) if a page does not exist

instead of crashing like BUF_READ_ANY_PAGE does

Function Documentation

UNIV_INTERN ulint buf_read_ahead_linear	(	ulint	space,
		ulint	zip_size,
		ulint	offset,
		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.

Returns: number of page read requests issued in: TRUE if we are inside ibuf routine

Parameters

space	in: space id
zip_size	in: compressed page size in bytes, or 0
offset	in: page number; see NOTE 3 above

UNIV_INTERN ulint buf_read_ahead_random	(	ulint	space,
		ulint	zip_size,
		ulint	offset,
		ibool	inside_ibuf
	)

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.

Returns: 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!; number of page read requests issued in: TRUE if we are inside ibuf routine

Parameters

space	in: space id
zip_size	in: compressed page size in bytes, or 0
offset	in: page number of a page which the current thread wants to access

UNIV_INTERN void buf_read_ibuf_merge_pages	(	bool	sync,
		const ulint *	space_ids,
		const ib_int64_t *	space_versions,
		const ulint *	page_nos,
		ulint	n_stored
	)

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. in: number of elements in the arrays

Parameters

sync	in: true if the caller wants this function to wait for the highest address page to get read in, before this function returns
space_ids	in: array of space ids
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
page_nos	in: array of page numbers to read, with the highest page number the last in the array

UNIV_INTERN ibool buf_read_page	(	ulint	space,
		ulint	zip_size,
		ulint	offset
	)

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.

Returns: TRUE if page has been read in, FALSE in case of failure in: page number

Parameters

space	in: space id
zip_size	in: compressed page size in bytes, or 0

UNIV_INTERN ibool buf_read_page_async	(	ulint	space,
		ulint	offset
	)

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.

Returns: TRUE if page has been read in, FALSE in case of failure in: page number

Parameters

space in: space id

UNIV_INTERN void buf_read_recv_pages	(	ibool	sync,
		ulint	space,
		ulint	zip_size,
		const ulint *	page_nos,
		ulint	n_stored
	)

Issues read requests for pages which recovery wants to read in. in: number of page numbers in the array

Parameters

sync	in: TRUE if the caller wants this function to wait for the highest address page to get read in, before this function returns
space	in: space id
zip_size	in: compressed page size in bytes, or 0
page_nos	in: array of page numbers to read, with the highest page number the last in the array

Macros

Functions

Detailed Description

Macro Definition Documentation

Function Documentation