path: root/innobase/row/row0vers.c

/******************************************************
Row versions

(c) 1997 Innobase Oy

Created 2/6/1997 Heikki Tuuri
*******************************************************/

#include "row0vers.h"

#ifdef UNIV_NONINL
#include "row0vers.ic"
#endif

#include "dict0dict.h"
#include "dict0boot.h"
#include "btr0btr.h"
#include "mach0data.h"
#include "trx0rseg.h"
#include "trx0trx.h"
#include "trx0roll.h"
#include "trx0undo.h"
#include "trx0purge.h"
#include "trx0rec.h"
#include "que0que.h"
#include "row0row.h"
#include "row0upd.h"
#include "rem0cmp.h"
#include "read0read.h"

/*********************************************************************
Finds out if an active transaction has inserted or modified a secondary
index record. NOTE: the kernel mutex is temporarily released in this
function! */

trx_t*
row_vers_impl_x_locked_off_kernel(
/*==============================*/
				/* out: NULL if committed, else the active
				transaction; NOTE that the kernel mutex is
				temporarily released! */
	rec_t*		rec,	/* in: record in a secondary index */
	dict_index_t*	index)	/* in: the secondary index */
{
	dict_index_t*	clust_index;
	rec_t*		clust_rec;
	rec_t*		version;
	rec_t*		prev_version;
	dulint		trx_id;
	dulint		prev_trx_id;
	mem_heap_t*	heap;
	mem_heap_t*	heap2;
	dtuple_t*	row;
	dtuple_t*	entry	= NULL; /* assignment to eliminate compiler
					warning */
	trx_t*		trx;
	ibool		vers_del;
	ibool		rec_del;
	ulint		err;
	mtr_t		mtr;
	
	ut_ad(mutex_own(&kernel_mutex));
	ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));

	mutex_exit(&kernel_mutex);

	mtr_start(&mtr);
	
	/* Search for the clustered index record: this is a time-consuming
	operation: therefore we release the kernel mutex; also, the release
	is required by the latching order convention. The latch on the
	clustered index locks the top of the stack of versions. We also
	reserve purge_latch to lock the bottom of the version stack. */	

	clust_rec = row_get_clust_rec(BTR_SEARCH_LEAF, rec, index,
							&clust_index, &mtr);
	ut_a(clust_rec);

	trx_id = row_get_rec_trx_id(clust_rec, clust_index);

	mtr_s_lock(&(purge_sys->latch), &mtr);

	mutex_enter(&kernel_mutex);
	
	if (!trx_is_active(trx_id)) {
		/* The transaction that modified or inserted clust_rec is no
		longer active: no implicit lock on rec */
		
		mtr_commit(&mtr);

		return(NULL);
	}

	/* We look up if some earlier version of the clustered index record
	would require rec to be in a different state (delete marked or
	unmarked, or not existing). If there is such a version, then rec was
	modified by the trx_id transaction, and it has an implicit x-lock on
	rec. Note that if clust_rec itself would require rec to be in a
	different state, then the trx_id transaction has not yet had time to
	modify rec, and does not necessarily have an implicit x-lock on rec. */

	rec_del = rec_get_deleted_flag(rec);
	trx = NULL;

	version = clust_rec;
	heap = NULL;

	for (;;) {
		mutex_exit(&kernel_mutex);

		/* While we retrieve an earlier version of clust_rec, we
		release the kernel mutex, because it may take time to access
		the disk. After the release, we have to check if the trx_id
		transaction is still active. We keep the semaphore in mtr on
		the clust_rec page, so that no other transaction can update
		it and get an implicit x-lock on rec. */

		heap2 = heap;
		heap = mem_heap_create(1024);

		err = trx_undo_prev_version_build(clust_rec, &mtr, version,
						clust_index, heap,
						&prev_version);
		if (heap2) {
			mem_heap_free(heap2); /* version was stored in heap2,
						if heap2 != NULL */
		}

		if (prev_version) {
			row = row_build(ROW_COPY_POINTERS, clust_index,
							prev_version, heap);
			entry = row_build_index_entry(row, index, heap);
		}

		mutex_enter(&kernel_mutex);

		if (!trx_is_active(trx_id)) {
			/* Transaction no longer active: no implicit x-lock */

			break;
		}

		/* If the transaction is still active, the previous version
		of clust_rec must be accessible if not a fresh insert; we
		may assert the following: */

		ut_ad(err == DB_SUCCESS);
						
		if (prev_version == NULL) {
			/* It was a freshly inserted version: there is an
			implicit x-lock on rec */

			trx = trx_get_on_id(trx_id);

			break;
		}

		/* If we get here, we know that the trx_id transaction is
		still active and it has modified prev_version. Let us check
		if prev_version would require rec to be in a different state. */

		vers_del = rec_get_deleted_flag(prev_version);

		if (0 == cmp_dtuple_rec(entry, rec)) {
			/* The delete marks of rec and prev_version should be
			equal for rec to be in the state required by
			prev_version */

			if (rec_del != vers_del) {
				trx = trx_get_on_id(trx_id);

				break;
			}
		} else if (!rec_del) {
			/* The delete mark should be set in rec for it to be
			in the state required by prev_version */

			trx = trx_get_on_id(trx_id);

			break;
		}

		prev_trx_id = row_get_rec_trx_id(prev_version, clust_index);

		if (0 != ut_dulint_cmp(trx_id, prev_trx_id)) {
			/* The versions modified by the trx_id transaction end
			to prev_version: no implicit x-lock */

			break;
		}

		version = prev_version;
	}/* for (;;) */

	mtr_commit(&mtr);
	mem_heap_free(heap);

	return(trx);
}

/*********************************************************************
Finds out if we must preserve a delete marked earlier version of a clustered
index record, because it is >= the purge view. */

ibool
row_vers_must_preserve_del_marked(
/*==============================*/
			/* out: TRUE if earlier version should be preserved */
	dulint	trx_id,	/* in: transaction id in the version */
	mtr_t*	mtr)	/* in: mtr holding the latch on the clustered index
			record; it will also hold the latch on purge_view */
{
	ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));

	mtr_s_lock(&(purge_sys->latch), mtr);

	if (trx_purge_update_undo_must_exist(trx_id)) {

		/* A purge operation is not yet allowed to remove this
		delete marked record */
			
		return(TRUE);
	}

	return(FALSE);
}

/*********************************************************************
Finds out if a version of the record, where the version >= the current
purge view, should have ientry as its secondary index entry. We check
if there is any not delete marked version of the record where the trx
id >= purge view, and the secondary index entry == ientry; exactly in
this case we return TRUE. */

ibool
row_vers_old_has_index_entry(
/*=========================*/
				/* out: TRUE if earlier version should have */
	ibool		also_curr,/* in: TRUE if also rec is included in the
				versions to search; otherwise only versions
				prior to it are searched */
	rec_t*		rec,	/* in: record in the clustered index; the
				caller must have a latch on the page */
	mtr_t*		mtr,	/* in: mtr holding the latch on rec; it will
				also hold the latch on purge_view */
	dict_index_t*	index,	/* in: the secondary index */
	dtuple_t*	ientry)	/* in: the secondary index entry */
{
	rec_t*		version;
	rec_t*		prev_version;
	dict_index_t*	clust_index;
	mem_heap_t*	heap;
	mem_heap_t*	heap2;
	dtuple_t*	row;
	dtuple_t*	entry;
	ulint		err;
	
	ut_ad(mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_X_FIX)
	   	|| mtr_memo_contains(mtr, buf_block_align(rec),
						MTR_MEMO_PAGE_S_FIX));
	ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
	mtr_s_lock(&(purge_sys->latch), mtr);

	clust_index = dict_table_get_first_index(index->table);

	if (also_curr && !rec_get_deleted_flag(rec)) {

		heap = mem_heap_create(1024);
		row = row_build(ROW_COPY_POINTERS, clust_index, rec, heap);
		entry = row_build_index_entry(row, index, heap);

 		/* NOTE that we cannot do the comparison as binary
		fields because the row is maybe being modified so that
		the clustered index record has already been updated
		to a different binary value in a char field, but the
		collation identifies the old and new value anyway! */

		if (dtuple_datas_are_ordering_equal(ientry, entry)) {

			mem_heap_free(heap);

			return(TRUE);
		}

		mem_heap_free(heap);
	}

	version = rec;
	heap = NULL;

	for (;;) {
		heap2 = heap;
		heap = mem_heap_create(1024);

		err = trx_undo_prev_version_build(rec, mtr, version,
						clust_index, heap,
						&prev_version);	
		if (heap2) {
			mem_heap_free(heap2); /* version was stored in heap2,
						if heap2 != NULL */
		}

		if ((err != DB_SUCCESS) || !prev_version) {
			/* Versions end here */

			mem_heap_free(heap);

			return(FALSE);
		}

		if (!rec_get_deleted_flag(prev_version)) {
			row = row_build(ROW_COPY_POINTERS, clust_index,
							prev_version, heap);
			entry = row_build_index_entry(row, index, heap);

 			/* NOTE that we cannot do the comparison as binary
			fields because maybe the secondary index record has
			already been updated to a different binary value in
			a char field, but the collation identifies the old
			and new value anyway! */

			if (dtuple_datas_are_ordering_equal(ientry, entry)) {

				mem_heap_free(heap);

				return(TRUE);
			}
		}

		version = prev_version;
	}
}

/*********************************************************************
Constructs the version of a clustered index record which a consistent
read should see. We assume that the trx id stored in rec is such that
the consistent read should not see rec in its present version. */

ulint
row_vers_build_for_consistent_read(
/*===============================*/
				/* out: DB_SUCCESS or DB_MISSING_HISTORY */
	rec_t*		rec,	/* in: record in a clustered index; the
				caller must have a latch on the page; this
				latch locks the top of the stack of versions
				of this records */
	mtr_t*		mtr,	/* in: mtr holding the latch on rec */
	dict_index_t*	index,	/* in: the clustered index */
	read_view_t*	view,	/* in: the consistent read view */
	mem_heap_t*	in_heap,/* in: memory heap from which the memory for
				old_vers is allocated; memory for possible
				intermediate versions is allocated and freed
				locally within the function */
	rec_t**		old_vers)/* out, own: old version, or NULL if the
				record does not exist in the view, that is,
				it was freshly inserted afterwards */
{
	rec_t*		version;
	rec_t*		prev_version;
	dulint		prev_trx_id;
	mem_heap_t*	heap;
	mem_heap_t*	heap2;
	byte*		buf;
	ulint		err;

	ut_ad(index->type & DICT_CLUSTERED);
	ut_ad(mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_X_FIX)
	   	|| mtr_memo_contains(mtr, buf_block_align(rec),
						MTR_MEMO_PAGE_S_FIX));
	ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
	ut_ad(!read_view_sees_trx_id(view, row_get_rec_trx_id(rec, index)));

	rw_lock_s_lock(&(purge_sys->latch));
	version = rec;
	heap = NULL;

	for (;;) {
		heap2 = heap;
		heap = mem_heap_create(1024);

		err = trx_undo_prev_version_build(rec, mtr, version, index,
							heap, &prev_version);
		if (heap2) {
			mem_heap_free(heap2); /* version was stored in heap2,
						if heap2 != NULL */
		}

		if (err != DB_SUCCESS) {
			break;
		}

		if (prev_version == NULL) {
			/* It was a freshly inserted version */
			*old_vers = NULL;
			err = DB_SUCCESS;

			break;
		}

		prev_trx_id = row_get_rec_trx_id(prev_version, index);

		if (read_view_sees_trx_id(view, prev_trx_id)) {

			/* The view already sees this version: we can copy
			it to in_heap and return */

			buf = mem_heap_alloc(in_heap, rec_get_size(
								prev_version));
			*old_vers = rec_copy(buf, prev_version);
			err = DB_SUCCESS;

			break;
		}

		version = prev_version;
	}/* for (;;) */

	mem_heap_free(heap);
	rw_lock_s_unlock(&(purge_sys->latch));

	return(err);
}