trx0undo.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

/******************************************************
Transaction undo log

(c) 1996 Innobase Oy

Created 3/26/1996 Heikki Tuuri
*******************************************************/

#include "trx0undo.h"

#ifdef UNIV_NONINL
#include "trx0undo.ic"
#endif

#include "fsp0fsp.h"
#include "mach0data.h"
#include "trx0rseg.h"
#include "trx0trx.h"
#include "srv0srv.h"
#include "trx0rec.h"
#include "trx0purge.h"
#include "trx0xa.h"

/* How should the old versions in the history list be managed?
   ----------------------------------------------------------
If each transaction is given a whole page for its update undo log, file
space consumption can be 10 times higher than necessary. Therefore,
partly filled update undo log pages should be reusable. But then there
is no way individual pages can be ordered so that the ordering agrees
with the serialization numbers of the transactions on the pages. Thus,
the history list must be formed of undo logs, not their header pages as
it was in the old implementation.
	However, on a single header page the transactions are placed in
the order of their serialization numbers. As old versions are purged, we
may free the page when the last transaction on the page has been purged.
	A problem is that the purge has to go through the transactions
in the serialization order. This means that we have to look through all
rollback segments for the one that has the smallest transaction number
in its history list.
	When should we do a purge? A purge is necessary when space is
running out in any of the rollback segments. Then we may have to purge
also old version which might be needed by some consistent read. How do
we trigger the start of a purge? When a transaction writes to an undo log,
it may notice that the space is running out. When a read view is closed,
it may make some history superfluous. The server can have an utility which
periodically checks if it can purge some history.
	In a parallellized purge we have the problem that a query thread
can remove a delete marked clustered index record before another query
thread has processed an earlier version of the record, which cannot then
be done because the row cannot be constructed from the clustered index
record. To avoid this problem, we will store in the update and delete mark
undo record also the columns necessary to construct the secondary index
entries which are modified.
	We can latch the stack of versions of a single clustered index record
by taking a latch on the clustered index page. As long as the latch is held,
no new versions can be added and no versions removed by undo. But, a purge
can still remove old versions from the bottom of the stack. */

/* How to protect rollback segments, undo logs, and history lists with
   -------------------------------------------------------------------
latches?
-------
The contention of the kernel mutex should be minimized. When a transaction
does its first insert or modify in an index, an undo log is assigned for it.
Then we must have an x-latch to the rollback segment header.
	When the transaction does more modifys or rolls back, the undo log is
protected with undo_mutex in the transaction.
	When the transaction commits, its insert undo log is either reset and
cached for a fast reuse, or freed. In these cases we must have an x-latch on
the rollback segment page. The update undo log is put to the history list. If
it is not suitable for reuse, its slot in the rollback segment is reset. In
both cases, an x-latch must be acquired on the rollback segment.
	The purge operation steps through the history list without modifying
it until a truncate operation occurs, which can remove undo logs from the end
of the list and release undo log segments. In stepping through the list,
s-latches on the undo log pages are enough, but in a truncate, x-latches must
be obtained on the rollback segment and individual pages. */

/************************************************************************
Initializes the fields in an undo log segment page. */
static
void
trx_undo_page_init(
/*================*/
	page_t* undo_page,	/* in: undo log segment page */
	ulint	type,		/* in: undo log segment type */
	mtr_t*	mtr);		/* in: mtr */
/************************************************************************
Creates and initializes an undo log memory object. */
static
trx_undo_t*
trx_undo_mem_create(
/*================*/
				/* out, own: the undo log memory object */
	trx_rseg_t*	rseg,	/* in: rollback segment memory object */
	ulint		id,	/* in: slot index within rseg */
	ulint		type,	/* in: type of the log: TRX_UNDO_INSERT or
				TRX_UNDO_UPDATE */
	dulint		trx_id,	/* in: id of the trx for which the undo log
				is created */	
	XID*		xid,    /* in: X/Open XA transaction identification*/
	ulint		page_no,/* in: undo log header page number */
	ulint		offset);/* in: undo log header byte offset on page */
/*******************************************************************
Initializes a cached insert undo log header page for new use. NOTE that this
function has its own log record type MLOG_UNDO_HDR_REUSE. You must NOT change
the operation of this function! */
static
ulint
trx_undo_insert_header_reuse(
/*=========================*/
				/* out: undo log header byte offset on page */
	page_t*	undo_page,	/* in: insert undo log segment header page,
				x-latched */
	dulint	trx_id,		/* in: transaction id */
	mtr_t*	mtr);		/* in: mtr */
/**************************************************************************
If an update undo log can be discarded immediately, this function frees the
space, resetting the page to the proper state for caching. */
static
void
trx_undo_discard_latest_update_undo(
/*================================*/
	page_t*	undo_page,	/* in: header page of an undo log of size 1 */
	mtr_t*	mtr);		/* in: mtr */


/***************************************************************************
Gets the previous record in an undo log from the previous page. */
static
trx_undo_rec_t*
trx_undo_get_prev_rec_from_prev_page(
/*=================================*/
				/* out: undo log record, the page s-latched,
				NULL if none */
	trx_undo_rec_t*	rec,	/* in: undo record */
	ulint		page_no,/* in: undo log header page number */
	ulint		offset,	/* in: undo log header offset on page */
	mtr_t*		mtr)	/* in: mtr */
{
	ulint	prev_page_no;
	page_t* prev_page;
	page_t*	undo_page;

	undo_page = buf_frame_align(rec);
	
	prev_page_no = flst_get_prev_addr(undo_page + TRX_UNDO_PAGE_HDR
						+ TRX_UNDO_PAGE_NODE, mtr)
					.page;

	if (prev_page_no == FIL_NULL) {

		return(NULL);
	}

	prev_page = trx_undo_page_get_s_latched(
					buf_frame_get_space_id(undo_page),
					prev_page_no, mtr);

	return(trx_undo_page_get_last_rec(prev_page, page_no, offset));
}

/***************************************************************************
Gets the previous record in an undo log. */

trx_undo_rec_t*
trx_undo_get_prev_rec(
/*==================*/
				/* out: undo log record, the page s-latched,
				NULL if none */
	trx_undo_rec_t*	rec,	/* in: undo record */
	ulint		page_no,/* in: undo log header page number */
	ulint		offset,	/* in: undo log header offset on page */
	mtr_t*		mtr)	/* in: mtr */
{
	trx_undo_rec_t*	prev_rec;
	
	prev_rec = trx_undo_page_get_prev_rec(rec, page_no, offset);

	if (prev_rec) {

		return(prev_rec);
	}

	/* We have to go to the previous undo log page to look for the
	previous record */

	return(trx_undo_get_prev_rec_from_prev_page(rec, page_no, offset,
									mtr));
}

/***************************************************************************
Gets the next record in an undo log from the next page. */
static
trx_undo_rec_t*
trx_undo_get_next_rec_from_next_page(
/*=================================*/
			/* out: undo log record, the page latched, NULL if
			none */
	page_t*	undo_page, /* in: undo log page */
	ulint	page_no,/* in: undo log header page number */
	ulint	offset,	/* in: undo log header offset on page */
	ulint	mode,	/* in: latch mode: RW_S_LATCH or RW_X_LATCH */
	mtr_t*	mtr)	/* in: mtr */
{
	trx_ulogf_t*	log_hdr;
	ulint		next_page_no;
	page_t* 	next_page;
	ulint		space;
	ulint		next;
	
	if (page_no == buf_frame_get_page_no(undo_page)) {

		log_hdr = undo_page + offset;
		next = mach_read_from_2(log_hdr + TRX_UNDO_NEXT_LOG);

		if (next != 0) {

			return(NULL);
		}
	}

	space = buf_frame_get_space_id(undo_page);

	next_page_no = flst_get_next_addr(undo_page + TRX_UNDO_PAGE_HDR
						+ TRX_UNDO_PAGE_NODE, mtr)
					.page;
	if (next_page_no == FIL_NULL) {

		return(NULL);
	}

	if (mode == RW_S_LATCH) {
		next_page = trx_undo_page_get_s_latched(space, next_page_no,
									mtr);
	} else {
		ut_ad(mode == RW_X_LATCH);
		next_page = trx_undo_page_get(space, next_page_no, mtr);
	}

	return(trx_undo_page_get_first_rec(next_page, page_no, offset));
}

/***************************************************************************
Gets the next record in an undo log. */

trx_undo_rec_t*
trx_undo_get_next_rec(
/*==================*/
				/* out: undo log record, the page s-latched,
				NULL if none */
	trx_undo_rec_t*	rec,	/* in: undo record */
	ulint		page_no,/* in: undo log header page number */
	ulint		offset,	/* in: undo log header offset on page */
	mtr_t*		mtr)	/* in: mtr */
{
	trx_undo_rec_t*	next_rec;
	
	next_rec = trx_undo_page_get_next_rec(rec, page_no, offset);

	if (next_rec) {
		return(next_rec);
	}

	return(trx_undo_get_next_rec_from_next_page(buf_frame_align(rec),
							page_no, offset,
							RW_S_LATCH, mtr));
}

/***************************************************************************
Gets the first record in an undo log. */

trx_undo_rec_t*
trx_undo_get_first_rec(
/*===================*/
			/* out: undo log record, the page latched, NULL if
			none */
	ulint	space,	/* in: undo log header space */	
	ulint	page_no,/* in: undo log header page number */
	ulint	offset,	/* in: undo log header offset on page */
	ulint	mode,	/* in: latching mode: RW_S_LATCH or RW_X_LATCH */
	mtr_t*	mtr)	/* in: mtr */
{
	page_t*		undo_page;
	trx_undo_rec_t*	rec;
	
	if (mode == RW_S_LATCH) {
		undo_page = trx_undo_page_get_s_latched(space, page_no, mtr);
	} else {
		undo_page = trx_undo_page_get(space, page_no, mtr);
	}

	rec = trx_undo_page_get_first_rec(undo_page, page_no, offset);

	if (rec) {
		return(rec);
	}

	return(trx_undo_get_next_rec_from_next_page(undo_page, page_no, offset,
								mode, mtr));
}

/*============== UNDO LOG FILE COPY CREATION AND FREEING ==================*/

/**************************************************************************
Writes the mtr log entry of an undo log page initialization. */
UNIV_INLINE
void
trx_undo_page_init_log(
/*====================*/
	page_t* undo_page,	/* in: undo log page */
	ulint	type,		/* in: undo log type */
	mtr_t*	mtr)		/* in: mtr */
{
	mlog_write_initial_log_record(undo_page, MLOG_UNDO_INIT, mtr);

	mlog_catenate_ulint_compressed(mtr, type);
}	

/***************************************************************
Parses the redo log entry of an undo log page initialization. */

byte*
trx_undo_parse_page_init(
/*======================*/
			/* out: end of log record or NULL */
	byte*	ptr,	/* in: buffer */
	byte*	end_ptr,/* in: buffer end */
	page_t*	page,	/* in: page or NULL */
	mtr_t*	mtr)	/* in: mtr or NULL */
{
	ulint	type;
	
	ptr = mach_parse_compressed(ptr, end_ptr, &type);

	if (ptr == NULL) {

		return(NULL);
	}

	if (page) {
		trx_undo_page_init(page, type, mtr);
	}

	return(ptr);
}	

/************************************************************************
Initializes the fields in an undo log segment page. */
static
void
trx_undo_page_init(
/*================*/
	page_t* undo_page,	/* in: undo log segment page */
	ulint	type,		/* in: undo log segment type */
	mtr_t*	mtr)		/* in: mtr */
{	
	trx_upagef_t*	page_hdr;
	
	page_hdr = undo_page + TRX_UNDO_PAGE_HDR;
					    
	mach_write_to_2(page_hdr + TRX_UNDO_PAGE_TYPE, type);

	mach_write_to_2(page_hdr + TRX_UNDO_PAGE_START,
				TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_HDR_SIZE);
	mach_write_to_2(page_hdr + TRX_UNDO_PAGE_FREE,
				TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_HDR_SIZE);

	fil_page_set_type(undo_page, FIL_PAGE_UNDO_LOG);
				
	trx_undo_page_init_log(undo_page, type, mtr);
}

/*******************************************************************
Creates a new undo log segment in file. */
static
page_t*
trx_undo_seg_create(
/*================*/
				/* out: segment header page x-latched, NULL
				if no space left */
	trx_rseg_t*	rseg __attribute__((unused)),/* in: rollback segment */
	trx_rsegf_t*	rseg_hdr,/* in: rollback segment header, page
				x-latched */
	ulint		type,	/* in: type of the segment: TRX_UNDO_INSERT or
				TRX_UNDO_UPDATE */
	ulint*		id,	/* out: slot index within rseg header */
	mtr_t*		mtr)	/* in: mtr */
{
	ulint		slot_no;
	ulint		space;
	page_t* 	undo_page;
	trx_upagef_t*	page_hdr;
	trx_usegf_t*	seg_hdr;
	ulint		n_reserved;
	ibool		success;
	
	ut_ad(mtr && id && rseg_hdr);
#ifdef UNIV_SYNC_DEBUG
	ut_ad(mutex_own(&(rseg->mutex)));
#endif /* UNIV_SYNC_DEBUG */

/*	fputs(type == TRX_UNDO_INSERT
		? "Creating insert undo log segment\n"
		: "Creating update undo log segment\n", stderr); */
	slot_no = trx_rsegf_undo_find_free(rseg_hdr, mtr);

	if (slot_no == ULINT_UNDEFINED) {
	        ut_print_timestamp(stderr);
	        fprintf(stderr,
"InnoDB: Warning: cannot find a free slot for an undo log. Do you have too\n"
"InnoDB: many active transactions running concurrently?\n");

		return(NULL);
	}

	space = buf_frame_get_space_id(rseg_hdr);

	success = fsp_reserve_free_extents(&n_reserved, space, 2, FSP_UNDO,
									mtr);
	if (!success) {

		return(NULL);
	}

	/* Allocate a new file segment for the undo log */
	undo_page = fseg_create_general(space, 0,
			TRX_UNDO_SEG_HDR + TRX_UNDO_FSEG_HEADER, TRUE, mtr);

	fil_space_release_free_extents(space, n_reserved);
			
	if (undo_page == NULL) {
		/* No space left */

		return(NULL);
	}

#ifdef UNIV_SYNC_DEBUG
	buf_page_dbg_add_level(undo_page, SYNC_TRX_UNDO_PAGE);
#endif /* UNIV_SYNC_DEBUG */

	page_hdr = undo_page + TRX_UNDO_PAGE_HDR;
	seg_hdr = undo_page + TRX_UNDO_SEG_HDR;

	trx_undo_page_init(undo_page, type, mtr);

	mlog_write_ulint(page_hdr + TRX_UNDO_PAGE_FREE,
				TRX_UNDO_SEG_HDR + TRX_UNDO_SEG_HDR_SIZE,
				MLOG_2BYTES, mtr);
	
	mlog_write_ulint(seg_hdr + TRX_UNDO_LAST_LOG, 0, MLOG_2BYTES, mtr);

	flst_init(seg_hdr + TRX_UNDO_PAGE_LIST, mtr);

	flst_add_last(seg_hdr + TRX_UNDO_PAGE_LIST,
					page_hdr + TRX_UNDO_PAGE_NODE, mtr);

	trx_rsegf_set_nth_undo(rseg_hdr, slot_no,
				buf_frame_get_page_no(undo_page), mtr);
	*id = slot_no;
	
	return(undo_page);
}

/**************************************************************************
Writes the mtr log entry of an undo log header initialization. */
UNIV_INLINE
void
trx_undo_header_create_log(
/*=======================*/
	page_t* undo_page,	/* in: undo log header page */
	dulint	trx_id,		/* in: transaction id */
	mtr_t*	mtr)		/* in: mtr */
{
	mlog_write_initial_log_record(undo_page, MLOG_UNDO_HDR_CREATE, mtr);