buf0rea.c

这是linux下运行的mysql软件包,可用于linux 下安装 php + mysql + apach 的网络配置

/******************************************************
The database buffer read

(c) 1995 Innobase Oy

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

#include "buf0rea.h"

#include "fil0fil.h"
#include "mtr0mtr.h"

#include "buf0buf.h"
#include "buf0flu.h"
#include "buf0lru.h"
#include "ibuf0ibuf.h"
#include "log0recv.h"
#include "trx0sys.h"
#include "os0file.h"
#include "srv0start.h"

extern ulint srv_read_ahead_rnd;
extern ulint srv_read_ahead_seq;
extern ulint srv_buf_pool_reads;

/* The size in blocks of the area where the random read-ahead algorithm counts
the accessed pages when deciding whether to read-ahead */
#define	BUF_READ_AHEAD_RANDOM_AREA	BUF_READ_AHEAD_AREA

/* There must be at least this many pages in buf_pool in the area to start
a random read-ahead */
#define BUF_READ_AHEAD_RANDOM_THRESHOLD	(5 + BUF_READ_AHEAD_RANDOM_AREA / 8)

/* The linear read-ahead area size */
#define	BUF_READ_AHEAD_LINEAR_AREA	BUF_READ_AHEAD_AREA

/* The linear read-ahead threshold */
#define BUF_READ_AHEAD_LINEAR_THRESHOLD	(3 * BUF_READ_AHEAD_LINEAR_AREA / 8)

/* If there are buf_pool->curr_size per the number below pending reads, then
read-ahead is not done: this is to prevent flooding the buffer pool with
i/o-fixed buffer blocks */
#define BUF_READ_AHEAD_PEND_LIMIT	2

/************************************************************************
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. */
static
ulint
buf_read_page_low(
/*==============*/
			/* out: 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 */
	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 */
	ib_longlong 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 */
{
	buf_block_t*	block;
	ulint		wake_later;

	*err = DB_SUCCESS;

	wake_later = mode & OS_AIO_SIMULATED_WAKE_LATER;
	mode = mode & ~OS_AIO_SIMULATED_WAKE_LATER;
	
	if (trx_doublewrite && space == TRX_SYS_SPACE
		&& (   (offset >= trx_doublewrite->block1
		        && offset < trx_doublewrite->block1
		     		+ TRX_SYS_DOUBLEWRITE_BLOCK_SIZE)
		    || (offset >= trx_doublewrite->block2
		        && offset < trx_doublewrite->block2
		     		+ TRX_SYS_DOUBLEWRITE_BLOCK_SIZE))) {
		ut_print_timestamp(stderr);
		fprintf(stderr,
"  InnoDB: Warning: trying to read doublewrite buffer page %lu\n",
			(ulong) offset);

		return(0);
	}

#ifdef UNIV_LOG_DEBUG
	if (space % 2 == 1) {
		/* We are updating a replicate space while holding the
		log mutex: the read must be handled before other reads
		which might incur ibuf operations and thus write to the log */

		fputs("Log debug: reading replicate page in sync mode\n",
			stderr);

		sync = TRUE;
	}
#endif
	if (ibuf_bitmap_page(offset) || trx_sys_hdr_page(space, offset)) {

		/* Trx sys header is so low in the latching order that we play
		safe and do not leave the i/o-completion to an asynchronous
		i/o-thread. Ibuf bitmap pages must always be read with
                syncronous i/o, to make sure they do not get involved in
                thread deadlocks. */
		
		sync = TRUE;
	}

	/* The following call will also check if the tablespace does not exist
	or is being dropped; if we succeed in initing the page in the buffer
	pool for read, then DISCARD cannot proceed until the read has
	completed */
	block = buf_page_init_for_read(err, mode, space, tablespace_version,
								offset);
	if (block == NULL) {
		
		return(0);
	}

#ifdef UNIV_DEBUG
	if (buf_debug_prints) {
		fprintf(stderr,
                        "Posting read request for page %lu, sync %lu\n",
							   (ulong) offset,
		       					   (ulong) sync);
	}
#endif

	ut_a(block->state == BUF_BLOCK_FILE_PAGE);

	*err = fil_io(OS_FILE_READ | wake_later,
			sync, space,
			offset, 0, UNIV_PAGE_SIZE,
			(void*)block->frame, (void*)block);
	ut_a(*err == DB_SUCCESS);

	if (sync) {
		/* The i/o is already completed when we arrive from
		fil_read */
		buf_page_io_complete(block);
	}
		
	return(1);
}	

/************************************************************************
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. */
static
ulint
buf_read_ahead_random(
/*==================*/
			/* out: 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 value > 0! */
	ulint	space,	/* in: space id */
	ulint	offset)	/* in: page number of a page which the current thread
			wants to access */
{
	ib_longlong	tablespace_version;
	buf_block_t*	block;
	ulint		recent_blocks	= 0;
	ulint		count;
	ulint		LRU_recent_limit;
	ulint		ibuf_mode;
	ulint		low, high;
	ulint		err;
	ulint		i;

	if (srv_startup_is_before_trx_rollback_phase) {
	        /* No read-ahead to avoid thread deadlocks */
	        return(0);
	}

	if (ibuf_bitmap_page(offset) || trx_sys_hdr_page(space, offset)) {

		/* If it is an ibuf bitmap page or trx sys hdr, we do
                no read-ahead, as that could break the ibuf page access
                order */

		return(0);
	}

	/* Remember the tablespace version before we ask te tablespace size
	below: if DISCARD + IMPORT changes the actual .ibd file meanwhile, we
	do not try to read outside the bounds of the tablespace! */

	tablespace_version = fil_space_get_version(space);

	low  = (offset / BUF_READ_AHEAD_RANDOM_AREA)
					* BUF_READ_AHEAD_RANDOM_AREA;
	high = (offset / BUF_READ_AHEAD_RANDOM_AREA + 1)
					* BUF_READ_AHEAD_RANDOM_AREA;
	if (high > fil_space_get_size(space)) {

		high = fil_space_get_size(space);
	}

	/* Get the minimum LRU_position field value for an initial segment
	of the LRU list, to determine which blocks have recently been added
	to the start of the list. */
	
	LRU_recent_limit = buf_LRU_get_recent_limit();

	mutex_enter(&(buf_pool->mutex));

	if (buf_pool->n_pend_reads >
			buf_pool->curr_size / BUF_READ_AHEAD_PEND_LIMIT) {
		mutex_exit(&(buf_pool->mutex));

		return(0);
	}	

	/* Count how many blocks in the area have been recently accessed,
	that is, reside near the start of the LRU list. */

	for (i = low; i < high; i++) {
		block = buf_page_hash_get(space, i);

		if ((block)
		    && (block->LRU_position > LRU_recent_limit)
		    && block->accessed) {

			recent_blocks++;
		}
	}

	mutex_exit(&(buf_pool->mutex));
	
	if (recent_blocks < BUF_READ_AHEAD_RANDOM_THRESHOLD) {
		/* Do nothing */

		return(0);
	}

	/* Read all the suitable blocks within the area */

	if (ibuf_inside()) {
		ibuf_mode = BUF_READ_IBUF_PAGES_ONLY;
	} else {
		ibuf_mode = BUF_READ_ANY_PAGE;
	}

	count = 0;

	for (i = low; i < high; i++) {
		/* It is only sensible to do read-ahead in the non-sync aio
		mode: hence FALSE as the first parameter */

		if (!ibuf_bitmap_page(i)) {
			count += buf_read_page_low(&err, FALSE, ibuf_mode
					| OS_AIO_SIMULATED_WAKE_LATER,
				        space, tablespace_version, i);
			if (err == DB_TABLESPACE_DELETED) {
				ut_print_timestamp(stderr);
				fprintf(stderr,
"  InnoDB: Warning: in random readahead trying to access tablespace\n"
"InnoDB: %lu page no. %lu,\n"
"InnoDB: but the tablespace does not exist or is just being dropped.\n",
					(ulong) space, (ulong) i);
			}
		}
	}

	/* In simulated aio we wake the aio handler threads only after
	queuing all aio requests, in native aio the following call does
	nothing: */
	
	os_aio_simulated_wake_handler_threads();

#ifdef UNIV_DEBUG
	if (buf_debug_prints && (count > 0)) {
		fprintf(stderr,
			"Random read-ahead space %lu offset %lu pages %lu\n",
						(ulong) space, (ulong) offset,
		       				(ulong) count);
	}
#endif /* UNIV_DEBUG */

        ++srv_read_ahead_rnd;
	return(count);
}

/************************************************************************
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 */
{
	ib_longlong	tablespace_version;
	ulint		count;
	ulint		count2;
	ulint		err;

	tablespace_version = fil_space_get_version(space);

	count = buf_read_ahead_random(space, offset);

	/* We do the i/o in the synchronous aio mode to save thread
	switches: hence TRUE */

	count2 = buf_read_page_low(&err, TRUE, BUF_READ_ANY_PAGE, space,
					tablespace_version, offset);
        srv_buf_pool_reads+= count2;
	if (err == DB_TABLESPACE_DELETED) {
	        ut_print_timestamp(stderr);
		fprintf(stderr,
"  InnoDB: Error: trying to access tablespace %lu page no. %lu,\n"
"InnoDB: but the tablespace does not exist or is just being dropped.\n",
				 (ulong) space, (ulong) offset);
	}

	/* Flush pages from the end of the LRU list if necessary */
	buf_flush_free_margin();

	return(count + count2);
}

/************************************************************************
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.