Import Percona XtraDB into the MariaDB source tree.

1 files changed, 538 insertions, 0 deletions

diff --git a/storage/xtradb/read/read0read.c b/storage/xtradb/read/read0read.c
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+/*****************************************************************************
+
+Copyright (c) 1997, 2009, Innobase Oy. All Rights Reserved.
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation; version 2 of the License.
+
+This program is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+Place, Suite 330, Boston, MA 02111-1307 USA
+
+*****************************************************************************/
+
+/******************************************************
+Cursor read
+
+Created 2/16/1997 Heikki Tuuri
+*******************************************************/
+
+#include "read0read.h"
+
+#ifdef UNIV_NONINL
+#include "read0read.ic"
+#endif
+
+#include "srv0srv.h"
+#include "trx0sys.h"
+
+/*
+-------------------------------------------------------------------------------
+FACT A: Cursor read view on a secondary index sees only committed versions
+-------
+of the records in the secondary index or those versions of rows created
+by transaction which created a cursor before cursor was created even
+if transaction which created the cursor has changed that clustered index page.
+
+PROOF: We must show that read goes always to the clustered index record
+to see that record is visible in the cursor read view. Consider e.g.
+following table and SQL-clauses:
+
+create table t1(a int not null, b int, primary key(a), index(b));
+insert into t1 values (1,1),(2,2);
+commit;
+
+Now consider that we have a cursor for a query
+
+select b from t1 where b >= 1;
+
+This query will use secondary key on the table t1. Now after the first fetch
+on this cursor if we do a update:
+
+update t1 set b = 5 where b = 2;
+
+Now second fetch of the cursor should not see record (2,5) instead it should
+see record (2,2).
+
+We also should show that if we have delete t1 where b = 5; we still
+can see record (2,2).
+
+When we access a secondary key record maximum transaction id is fetched
+from this record and this trx_id is compared to up_limit_id in the view.
+If trx_id in the record is greater or equal than up_limit_id in the view
+cluster record is accessed.  Because trx_id of the creating
+transaction is stored when this view was created to the list of
+trx_ids not seen by this read view previous version of the
+record is requested to be built. This is build using clustered record.
+If the secondary key record is delete  marked it's corresponding
+clustered record can be already be purged only if records
+trx_id < low_limit_no. Purge can't remove any record deleted by a
+transaction which was active when cursor was created. But, we still
+may have a deleted secondary key record but no clustered record. But,
+this is not a problem because this case is handled in
+row_sel_get_clust_rec() function which is called
+whenever we note that this read view does not see trx_id in the
+record. Thus, we see correct version. Q. E. D.
+
+-------------------------------------------------------------------------------
+FACT B: Cursor read view on a clustered index sees only committed versions
+-------
+of the records in the clustered index or those versions of rows created
+by transaction which created a cursor before cursor was created even
+if transaction which created the cursor has changed that clustered index page.
+
+PROOF:  Consider e.g.following table and SQL-clauses:
+
+create table t1(a int not null, b int, primary key(a));
+insert into t1 values (1),(2);
+commit;
+
+Now consider that we have a cursor for a query
+
+select a from t1 where a >= 1;
+
+This query will use clustered key on the table t1. Now after the first fetch
+on this cursor if we do a update:
+
+update t1 set a = 5 where a = 2;
+
+Now second fetch of the cursor should not see record (5) instead it should
+see record (2).
+
+We also should show that if we have execute delete t1 where a = 5; after
+the cursor is opened we still can see record (2).
+
+When accessing clustered record we always check if this read view sees
+trx_id stored to clustered record. By default we don't see any changes
+if record trx_id >= low_limit_id i.e. change was made transaction
+which started after transaction which created the cursor. If row
+was changed by the future transaction a previous version of the
+clustered record is created. Thus we see only committed version in
+this case. We see all changes made by committed transactions i.e.
+record trx_id < up_limit_id. In this case we don't need to do anything,
+we already see correct version of the record. We don't see any changes
+made by active transaction except creating transaction. We have stored
+trx_id of creating transaction to list of trx_ids when this view was
+created. Thus we can easily see if this record was changed by the
+creating transaction. Because we already have clustered record we can
+access roll_ptr. Using this roll_ptr we can fetch undo record.
+We can now check that undo_no of the undo record is less than undo_no of the
+trancaction which created a view when cursor was created. We see this
+clustered record only in case when record undo_no is less than undo_no
+in the view. If this is not true we build based on undo_rec previous
+version of the record. This record is found because purge can't remove
+records accessed by active transaction. Thus we see correct version. Q. E. D.
+-------------------------------------------------------------------------------
+FACT C: Purge does not remove any delete marked row that is visible
+-------
+to cursor view.
+
+TODO: proof this
+
+*/
+
+/*************************************************************************
+Creates a read view object. */
+UNIV_INLINE
+read_view_t*
+read_view_create_low(
+/*=================*/
+				/* out, own: read view struct */
+	ulint		n,	/* in: number of cells in the trx_ids array */
+	mem_heap_t*	heap)	/* in: memory heap from which allocated */
+{
+	read_view_t*	view;
+
+	view = mem_heap_alloc(heap, sizeof(read_view_t));
+
+	view->n_trx_ids = n;
+	view->trx_ids = mem_heap_alloc(heap, n * sizeof(dulint));
+
+	return(view);
+}
+
+/*************************************************************************
+Makes a copy of the oldest existing read view, with the exception that also
+the creating trx of the oldest view is set as not visible in the 'copied'
+view. Opens a new view if no views currently exist. The view must be closed
+with ..._close. This is used in purge. */
+UNIV_INTERN
+read_view_t*
+read_view_oldest_copy_or_open_new(
+/*==============================*/
+					/* out, own: read view struct */
+	dulint		cr_trx_id,	/* in: trx_id of creating
+					transaction, or (0, 0) used in purge*/
+	mem_heap_t*	heap)		/* in: memory heap from which
+					allocated */
+{
+	read_view_t*	old_view;
+	read_view_t*	view_copy;
+	ibool		needs_insert	= TRUE;
+	ulint		insert_done	= 0;
+	ulint		n;
+	ulint		i;
+
+	ut_ad(mutex_own(&kernel_mutex));
+
+	old_view = UT_LIST_GET_LAST(trx_sys->view_list);
+
+	if (old_view == NULL) {
+
+		return(read_view_open_now(cr_trx_id, heap));
+	}
+
+	n = old_view->n_trx_ids;
+
+	if (!ut_dulint_is_zero(old_view->creator_trx_id)) {
+		n++;
+	} else {
+		needs_insert = FALSE;
+	}
+
+	view_copy = read_view_create_low(n, heap);
+
+	/* Insert the id of the creator in the right place of the descending
+	array of ids, if needs_insert is TRUE: */
+
+	i = 0;
+	while (i < n) {
+		if (needs_insert
+		    && (i >= old_view->n_trx_ids
+			|| ut_dulint_cmp(old_view->creator_trx_id,
+					 read_view_get_nth_trx_id(old_view, i))
+			> 0)) {
+
+			read_view_set_nth_trx_id(view_copy, i,
+						 old_view->creator_trx_id);
+			needs_insert = FALSE;
+			insert_done = 1;
+		} else {
+			read_view_set_nth_trx_id(view_copy, i,
+						 read_view_get_nth_trx_id(
+							 old_view,
+							 i - insert_done));
+		}
+
+		i++;
+	}
+
+	view_copy->creator_trx_id = cr_trx_id;
+
+	view_copy->low_limit_no = old_view->low_limit_no;
+	view_copy->low_limit_id = old_view->low_limit_id;
+
+
+	if (n > 0) {
+		/* The last active transaction has the smallest id: */
+		view_copy->up_limit_id = read_view_get_nth_trx_id(
+			view_copy, n - 1);
+	} else {
+		view_copy->up_limit_id = old_view->up_limit_id;
+	}
+
+	UT_LIST_ADD_LAST(view_list, trx_sys->view_list, view_copy);
+
+	return(view_copy);
+}
+
+/*************************************************************************
+Opens a read view where exactly the transactions serialized before this
+point in time are seen in the view. */
+UNIV_INTERN
+read_view_t*
+read_view_open_now(
+/*===============*/
+					/* out, own: read view struct */
+	dulint		cr_trx_id,	/* in: trx_id of creating
+					transaction, or (0, 0) used in
+					purge */
+	mem_heap_t*	heap)		/* in: memory heap from which
+					allocated */
+{
+	read_view_t*	view;
+	trx_t*		trx;
+	ulint		n;
+
+	ut_ad(mutex_own(&kernel_mutex));
+
+	view = read_view_create_low(UT_LIST_GET_LEN(trx_sys->trx_list), heap);
+
+	view->creator_trx_id = cr_trx_id;
+	view->type = VIEW_NORMAL;
+	view->undo_no = ut_dulint_zero;
+
+	/* No future transactions should be visible in the view */
+
+	view->low_limit_no = trx_sys->max_trx_id;
+	view->low_limit_id = view->low_limit_no;
+
+	n = 0;
+	trx = UT_LIST_GET_FIRST(trx_sys->trx_list);
+
+	/* No active transaction should be visible, except cr_trx */
+
+	while (trx) {
+		if (ut_dulint_cmp(trx->id, cr_trx_id) != 0
+		    && (trx->conc_state == TRX_ACTIVE
+			|| trx->conc_state == TRX_PREPARED)) {
+
+			read_view_set_nth_trx_id(view, n, trx->id);
+
+			n++;
+
+			/* NOTE that a transaction whose trx number is <
+			trx_sys->max_trx_id can still be active, if it is
+			in the middle of its commit! Note that when a
+			transaction starts, we initialize trx->no to
+			ut_dulint_max. */
+
+			if (ut_dulint_cmp(view->low_limit_no, trx->no) > 0) {
+
+				view->low_limit_no = trx->no;
+			}
+		}
+
+		trx = UT_LIST_GET_NEXT(trx_list, trx);
+	}
+
+	view->n_trx_ids = n;
+
+	if (n > 0) {
+		/* The last active transaction has the smallest id: */
+		view->up_limit_id = read_view_get_nth_trx_id(view, n - 1);
+	} else {
+		view->up_limit_id = view->low_limit_id;
+	}
+
+
+	UT_LIST_ADD_FIRST(view_list, trx_sys->view_list, view);
+
+	return(view);
+}
+
+/*************************************************************************
+Closes a read view. */
+UNIV_INTERN
+void
+read_view_close(
+/*============*/
+	read_view_t*	view)	/* in: read view */
+{
+	ut_ad(mutex_own(&kernel_mutex));
+
+	UT_LIST_REMOVE(view_list, trx_sys->view_list, view);
+}
+
+/*************************************************************************
+Closes a consistent read view for MySQL. This function is called at an SQL
+statement end if the trx isolation level is <= TRX_ISO_READ_COMMITTED. */
+UNIV_INTERN
+void
+read_view_close_for_mysql(
+/*======================*/
+	trx_t*	trx)	/* in: trx which has a read view */
+{
+	ut_a(trx->global_read_view);
+
+	mutex_enter(&kernel_mutex);
+
+	read_view_close(trx->global_read_view);
+
+	mem_heap_empty(trx->global_read_view_heap);
+
+	trx->read_view = NULL;
+	trx->global_read_view = NULL;
+
+	mutex_exit(&kernel_mutex);
+}
+
+/*************************************************************************
+Prints a read view to stderr. */
+UNIV_INTERN
+void
+read_view_print(
+/*============*/
+	read_view_t*	view)	/* in: read view */
+{
+	ulint	n_ids;
+	ulint	i;
+
+	if (view->type == VIEW_HIGH_GRANULARITY) {
+		fprintf(stderr,
+			"High-granularity read view undo_n:o %lu %lu\n",
+			(ulong) ut_dulint_get_high(view->undo_no),
+			(ulong) ut_dulint_get_low(view->undo_no));
+	} else {
+		fprintf(stderr, "Normal read view\n");
+	}
+
+	fprintf(stderr, "Read view low limit trx n:o %lu %lu\n",
+		(ulong) ut_dulint_get_high(view->low_limit_no),
+		(ulong) ut_dulint_get_low(view->low_limit_no));
+
+	fprintf(stderr, "Read view up limit trx id " TRX_ID_FMT "\n",
+		TRX_ID_PREP_PRINTF(view->up_limit_id));
+
+	fprintf(stderr, "Read view low limit trx id " TRX_ID_FMT "\n",
+		TRX_ID_PREP_PRINTF(view->low_limit_id));
+
+	fprintf(stderr, "Read view individually stored trx ids:\n");
+
+	n_ids = view->n_trx_ids;
+
+	for (i = 0; i < n_ids; i++) {
+		fprintf(stderr, "Read view trx id " TRX_ID_FMT "\n",
+			TRX_ID_PREP_PRINTF(
+				read_view_get_nth_trx_id(view, i)));
+	}
+}
+
+/*************************************************************************
+Create a high-granularity consistent cursor view for mysql to be used
+in cursors. In this consistent read view modifications done by the
+creating transaction after the cursor is created or future transactions
+are not visible. */
+UNIV_INTERN
+cursor_view_t*
+read_cursor_view_create_for_mysql(
+/*==============================*/
+	trx_t*	cr_trx)	/* in: trx where cursor view is created */
+{
+	cursor_view_t*	curview;
+	read_view_t*	view;
+	mem_heap_t*	heap;
+	trx_t*		trx;
+	ulint		n;
+
+	ut_a(cr_trx);
+
+	/* Use larger heap than in trx_create when creating a read_view
+	because cursors are quite long. */
+
+	heap = mem_heap_create(512);
+
+	curview = (cursor_view_t*) mem_heap_alloc(heap, sizeof(cursor_view_t));
+	curview->heap = heap;
+
+	/* Drop cursor tables from consideration when evaluating the need of
+	auto-commit */
+	curview->n_mysql_tables_in_use = cr_trx->n_mysql_tables_in_use;
+	cr_trx->n_mysql_tables_in_use = 0;
+
+	mutex_enter(&kernel_mutex);
+
+	curview->read_view = read_view_create_low(
+		UT_LIST_GET_LEN(trx_sys->trx_list), curview->heap);
+
+	view = curview->read_view;
+	view->creator_trx_id = cr_trx->id;
+	view->type = VIEW_HIGH_GRANULARITY;
+	view->undo_no = cr_trx->undo_no;
+
+	/* No future transactions should be visible in the view */
+
+	view->low_limit_no = trx_sys->max_trx_id;
+	view->low_limit_id = view->low_limit_no;
+
+	n = 0;
+	trx = UT_LIST_GET_FIRST(trx_sys->trx_list);
+
+	/* No active transaction should be visible */
+
+	while (trx) {
+
+		if (trx->conc_state == TRX_ACTIVE
+		    || trx->conc_state == TRX_PREPARED) {
+
+			read_view_set_nth_trx_id(view, n, trx->id);
+
+			n++;
+
+			/* NOTE that a transaction whose trx number is <
+			trx_sys->max_trx_id can still be active, if it is
+			in the middle of its commit! Note that when a
+			transaction starts, we initialize trx->no to
+			ut_dulint_max. */
+
+			if (ut_dulint_cmp(view->low_limit_no, trx->no) > 0) {
+
+				view->low_limit_no = trx->no;
+			}
+		}
+
+		trx = UT_LIST_GET_NEXT(trx_list, trx);
+	}
+
+	view->n_trx_ids = n;
+
+	if (n > 0) {
+		/* The last active transaction has the smallest id: */
+		view->up_limit_id = read_view_get_nth_trx_id(view, n - 1);
+	} else {
+		view->up_limit_id = view->low_limit_id;
+	}
+
+	UT_LIST_ADD_FIRST(view_list, trx_sys->view_list, view);
+
+	mutex_exit(&kernel_mutex);
+
+	return(curview);
+}
+
+/*************************************************************************
+Close a given consistent cursor view for mysql and restore global read view
+back to a transaction read view. */
+UNIV_INTERN
+void
+read_cursor_view_close_for_mysql(
+/*=============================*/
+	trx_t*		trx,	/* in: trx */
+	cursor_view_t*	curview)/* in: cursor view to be closed */
+{
+	ut_a(curview);
+	ut_a(curview->read_view);
+	ut_a(curview->heap);
+
+	/* Add cursor's tables to the global count of active tables that
+	belong to this transaction */
+	trx->n_mysql_tables_in_use += curview->n_mysql_tables_in_use;
+
+	mutex_enter(&kernel_mutex);
+
+	read_view_close(curview->read_view);
+	trx->read_view = trx->global_read_view;
+
+	mutex_exit(&kernel_mutex);
+
+	mem_heap_free(curview->heap);
+}
+
+/*************************************************************************
+This function sets a given consistent cursor view to a transaction
+read view if given consistent cursor view is not NULL. Otherwise, function
+restores a global read view to a transaction read view. */
+UNIV_INTERN
+void
+read_cursor_set_for_mysql(
+/*======================*/
+	trx_t*		trx,	/* in: transaction where cursor is set */
+	cursor_view_t*	curview)/* in: consistent cursor view to be set */
+{
+	ut_a(trx);
+
+	mutex_enter(&kernel_mutex);
+
+	if (UNIV_LIKELY(curview != NULL)) {
+		trx->read_view = curview->read_view;
+	} else {
+		trx->read_view = trx->global_read_view;
+	}
+
+	mutex_exit(&kernel_mutex);
+}