/*****************************************************************************

Copyright (c) 1996, 2014, Oracle and/or its affiliates. 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.,
51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA

*****************************************************************************/

/**************************************************//**
@file trx/trx0roll.cc
Transaction rollback

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

#include "trx0roll.h"

#ifdef UNIV_NONINL
#include "trx0roll.ic"
#endif

#include "fsp0fsp.h"
#include "mach0data.h"
#include "trx0rseg.h"
#include "trx0trx.h"
#include "trx0undo.h"
#include "trx0rec.h"
#include "que0que.h"
#include "usr0sess.h"
#include "srv0start.h"
#include "read0read.h"
#include "row0undo.h"
#include "row0mysql.h"
#include "lock0lock.h"
#include "pars0pars.h"
#include "srv0mon.h"
#include "trx0sys.h"

/** This many pages must be undone before a truncate is tried within
rollback */
#define TRX_ROLL_TRUNC_THRESHOLD	1

/** In crash recovery, the current trx to be rolled back; NULL otherwise */
static const trx_t*	trx_roll_crash_recv_trx	= NULL;

/** In crash recovery we set this to the undo n:o of the current trx to be
rolled back. Then we can print how many % the rollback has progressed. */
static undo_no_t	trx_roll_max_undo_no;

/** Auxiliary variable which tells the previous progress % we printed */
static ulint		trx_roll_progress_printed_pct;

/****************************************************************//**
Finishes a transaction rollback. */
static
void
trx_rollback_finish(
/*================*/
	trx_t*		trx);	/*!< in: transaction */

/*******************************************************************//**
Rollback a transaction used in MySQL. */
static
void
trx_rollback_to_savepoint_low(
/*==========================*/
	trx_t*		trx,	/*!< in: transaction handle */
	trx_savept_t*	savept)	/*!< in: pointer to savepoint undo number, if
				partial rollback requested, or NULL for
				complete rollback */
{
	que_thr_t*	thr;
	mem_heap_t*	heap;
	roll_node_t*	roll_node;

	heap = mem_heap_create(512);

	roll_node = roll_node_create(heap);

	if (savept != NULL) {
		roll_node->partial = TRUE;
		roll_node->savept = *savept;
		assert_trx_in_list(trx);
	}  else {
		assert_trx_nonlocking_or_in_list(trx);
	}

	trx->error_state = DB_SUCCESS;

	if (trx->insert_undo || trx->update_undo) {
		thr = pars_complete_graph_for_exec(roll_node, trx, heap);

		ut_a(thr == que_fork_start_command(
			static_cast<que_fork_t*>(que_node_get_parent(thr))));

		que_run_threads(thr);

		ut_a(roll_node->undo_thr != NULL);
		que_run_threads(roll_node->undo_thr);

		/* Free the memory reserved by the undo graph. */
		que_graph_free(static_cast<que_t*>(
				       roll_node->undo_thr->common.parent));
	}

	if (savept == NULL) {
		trx_rollback_finish(trx);
		MONITOR_INC(MONITOR_TRX_ROLLBACK);
	} else {
		trx->lock.que_state = TRX_QUE_RUNNING;
		MONITOR_INC(MONITOR_TRX_ROLLBACK_SAVEPOINT);
	}

	ut_a(trx->error_state == DB_SUCCESS);
	ut_a(trx->lock.que_state == TRX_QUE_RUNNING);

	mem_heap_free(heap);

	/* There might be work for utility threads.*/
	srv_active_wake_master_thread();

	MONITOR_DEC(MONITOR_TRX_ACTIVE);
}

/*******************************************************************//**
Rollback a transaction to a given savepoint or do a complete rollback.
@return	error code or DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_rollback_to_savepoint(
/*======================*/
	trx_t*		trx,	/*!< in: transaction handle */
	trx_savept_t*	savept)	/*!< in: pointer to savepoint undo number, if
				partial rollback requested, or NULL for
				complete rollback */
{
	ut_ad(!trx_mutex_own(trx));

	trx_start_if_not_started_xa(trx);

	trx_rollback_to_savepoint_low(trx, savept);

	return(trx->error_state);
}

/*******************************************************************//**
Rollback a transaction used in MySQL.
@return	error code or DB_SUCCESS */
static
dberr_t
trx_rollback_for_mysql_low(
/*=======================*/
	trx_t*	trx)	/*!< in/out: transaction */
{
	trx->op_info = "rollback";

	/* If we are doing the XA recovery of prepared transactions,
	then the transaction object does not have an InnoDB session
	object, and we set a dummy session that we use for all MySQL
	transactions. */

	trx_rollback_to_savepoint_low(trx, NULL);

	trx->op_info = "";

	ut_a(trx->error_state == DB_SUCCESS);

	return(trx->error_state);
}

/*******************************************************************//**
Rollback a transaction used in MySQL.
@return	error code or DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_rollback_for_mysql(
/*===================*/
	trx_t*	trx)	/*!< in/out: transaction */
{
	/* We are reading trx->state without holding trx_sys->mutex
	here, because the rollback should be invoked for a running
	active MySQL transaction (or recovered prepared transaction)
	that is associated with the current thread. */

	switch (trx->state) {
	case TRX_STATE_NOT_STARTED:
		ut_ad(trx->in_mysql_trx_list);
		return(DB_SUCCESS);

	case TRX_STATE_ACTIVE:
		ut_ad(trx->in_mysql_trx_list);
		assert_trx_nonlocking_or_in_list(trx);
		return(trx_rollback_for_mysql_low(trx));

	case TRX_STATE_PREPARED:
		ut_ad(!trx_is_autocommit_non_locking(trx));
		return(trx_rollback_for_mysql_low(trx));

	case TRX_STATE_COMMITTED_IN_MEMORY:
		assert_trx_in_list(trx);
		break;
	}

	ut_error;
	return(DB_CORRUPTION);
}

/*******************************************************************//**
Rollback the latest SQL statement for MySQL.
@return	error code or DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_rollback_last_sql_stat_for_mysql(
/*=================================*/
	trx_t*	trx)	/*!< in/out: transaction */
{
	dberr_t	err;

	/* We are reading trx->state without holding trx_sys->mutex
	here, because the statement rollback should be invoked for a
	running active MySQL transaction that is associated with the
	current thread. */
	ut_ad(trx->in_mysql_trx_list);

	switch (trx->state) {
	case TRX_STATE_NOT_STARTED:
		return(DB_SUCCESS);
	case TRX_STATE_ACTIVE:
		assert_trx_nonlocking_or_in_list(trx);

		trx->op_info = "rollback of SQL statement";

		err = trx_rollback_to_savepoint(
			trx, &trx->last_sql_stat_start);

		if (trx->fts_trx) {
			fts_savepoint_rollback_last_stmt(trx);
		}

		/* The following call should not be needed,
		but we play it safe: */
		trx_mark_sql_stat_end(trx);

		trx->op_info = "";

		return(err);
	case TRX_STATE_PREPARED:
	case TRX_STATE_COMMITTED_IN_MEMORY:
		/* The statement rollback is only allowed on an ACTIVE
		transaction, not a PREPARED or COMMITTED one. */
		break;
	}

	ut_error;
	return(DB_CORRUPTION);
}

/*******************************************************************//**
Search for a savepoint using name.
@return savepoint if found else NULL */
static
trx_named_savept_t*
trx_savepoint_find(
/*===============*/
	trx_t*		trx,			/*!< in: transaction */
	const char*	name)			/*!< in: savepoint name */
{
	trx_named_savept_t*	savep;

	for (savep = UT_LIST_GET_FIRST(trx->trx_savepoints);
	     savep != NULL;
	     savep = UT_LIST_GET_NEXT(trx_savepoints, savep)) {

		if (0 == ut_strcmp(savep->name, name)) {
			return(savep);
		}
	}

	return(NULL);
}

/*******************************************************************//**
Frees a single savepoint struct. */
static
void
trx_roll_savepoint_free(
/*=====================*/
	trx_t*			trx,	/*!< in: transaction handle */
	trx_named_savept_t*	savep)	/*!< in: savepoint to free */
{
	UT_LIST_REMOVE(trx_savepoints, trx->trx_savepoints, savep);
	mem_free(savep->name);
	mem_free(savep);
}

/*******************************************************************//**
Frees savepoint structs starting from savep. */
UNIV_INTERN
void
trx_roll_savepoints_free(
/*=====================*/
	trx_t*			trx,	/*!< in: transaction handle */
	trx_named_savept_t*	savep)	/*!< in: free all savepoints starting
					with this savepoint i*/
{
	while (savep != NULL) {
		trx_named_savept_t*	next_savep;

		next_savep = UT_LIST_GET_NEXT(trx_savepoints, savep);

		trx_roll_savepoint_free(trx, savep);

		savep = next_savep;
	}
}

/*******************************************************************//**
Rolls back a transaction back to a named savepoint. Modifications after the
savepoint are undone but InnoDB does NOT release the corresponding locks
which are stored in memory. If a lock is 'implicit', that is, a new inserted
row holds a lock where the lock information is carried by the trx id stored in
the row, these locks are naturally released in the rollback. Savepoints which
were set after this savepoint are deleted.
@return if no savepoint of the name found then DB_NO_SAVEPOINT,
otherwise DB_SUCCESS */
static __attribute__((nonnull, warn_unused_result))
dberr_t
trx_rollback_to_savepoint_for_mysql_low(
/*====================================*/
	trx_t*			trx,	/*!< in/out: transaction */
	trx_named_savept_t*	savep,	/*!< in/out: savepoint */
	ib_int64_t*		mysql_binlog_cache_pos)
					/*!< out: the MySQL binlog
					cache position corresponding
					to this savepoint; MySQL needs
					this information to remove the
					binlog entries of the queries
					executed after the savepoint */
{
	dberr_t	err;

	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
	ut_ad(trx->in_mysql_trx_list);

	/* Free all savepoints strictly later than savep. */

	trx_roll_savepoints_free(
		trx, UT_LIST_GET_NEXT(trx_savepoints, savep));

	*mysql_binlog_cache_pos = savep->mysql_binlog_cache_pos;

	trx->op_info = "rollback to a savepoint";

	err = trx_rollback_to_savepoint(trx, &savep->savept);

	/* Store the current undo_no of the transaction so that
	we know where to roll back if we have to roll back the
	next SQL statement: */

	trx_mark_sql_stat_end(trx);

	trx->op_info = "";

	return(err);
}

/*******************************************************************//**
Rolls back a transaction back to a named savepoint. Modifications after the
savepoint are undone but InnoDB does NOT release the corresponding locks
which are stored in memory. If a lock is 'implicit', that is, a new inserted
row holds a lock where the lock information is carried by the trx id stored in
the row, these locks are naturally released in the rollback. Savepoints which
were set after this savepoint are deleted.
@return if no savepoint of the name found then DB_NO_SAVEPOINT,
otherwise DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_rollback_to_savepoint_for_mysql(
/*================================*/
	trx_t*		trx,			/*!< in: transaction handle */
	const char*	savepoint_name,		/*!< in: savepoint name */
	ib_int64_t*	mysql_binlog_cache_pos)	/*!< out: the MySQL binlog cache
						position corresponding to this
						savepoint; MySQL needs this
						information to remove the
						binlog entries of the queries
						executed after the savepoint */
{
	trx_named_savept_t*	savep;

	/* We are reading trx->state without holding trx_sys->mutex
	here, because the savepoint rollback should be invoked for a
	running active MySQL transaction that is associated with the
	current thread. */
	ut_ad(trx->in_mysql_trx_list);

	savep = trx_savepoint_find(trx, savepoint_name);

	if (savep == NULL) {
		return(DB_NO_SAVEPOINT);
	}

	switch (trx->state) {
	case TRX_STATE_NOT_STARTED:
		ut_print_timestamp(stderr);
		fputs("  InnoDB: Error: transaction has a savepoint ", stderr);
		ut_print_name(stderr, trx, FALSE, savep->name);
		fputs(" though it is not started\n", stderr);
		return(DB_ERROR);
	case TRX_STATE_ACTIVE:
		return(trx_rollback_to_savepoint_for_mysql_low(
				trx, savep, mysql_binlog_cache_pos));
	case TRX_STATE_PREPARED:
	case TRX_STATE_COMMITTED_IN_MEMORY:
		/* The savepoint rollback is only allowed on an ACTIVE
		transaction, not a PREPARED or COMMITTED one. */
		break;
	}

	ut_error;
	return(DB_CORRUPTION);
}

/*******************************************************************//**
Creates a named savepoint. If the transaction is not yet started, starts it.
If there is already a savepoint of the same name, this call erases that old
savepoint and replaces it with a new. Savepoints are deleted in a transaction
commit or rollback.
@return	always DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_savepoint_for_mysql(
/*====================*/
	trx_t*		trx,			/*!< in: transaction handle */
	const char*	savepoint_name,		/*!< in: savepoint name */
	ib_int64_t	binlog_cache_pos)	/*!< in: MySQL binlog cache
						position corresponding to this
						connection at the time of the
						savepoint */
{
	trx_named_savept_t*	savep;

	trx_start_if_not_started_xa(trx);

	savep = trx_savepoint_find(trx, savepoint_name);

	if (savep) {
		/* There is a savepoint with the same name: free that */

		UT_LIST_REMOVE(trx_savepoints, trx->trx_savepoints, savep);

		mem_free(savep->name);
		mem_free(savep);
	}

	/* Create a new savepoint and add it as the last in the list */

	savep = static_cast<trx_named_savept_t*>(mem_alloc(sizeof(*savep)));

	savep->name = mem_strdup(savepoint_name);

	savep->savept = trx_savept_take(trx);

	savep->mysql_binlog_cache_pos = binlog_cache_pos;

	UT_LIST_ADD_LAST(trx_savepoints, trx->trx_savepoints, savep);

	return(DB_SUCCESS);
}

/*******************************************************************//**
Releases only the named savepoint. Savepoints which were set after this
savepoint are left as is.
@return if no savepoint of the name found then DB_NO_SAVEPOINT,
otherwise DB_SUCCESS */
UNIV_INTERN
dberr_t
trx_release_savepoint_for_mysql(
/*============================*/
	trx_t*		trx,			/*!< in: transaction handle */
	const char*	savepoint_name)		/*!< in: savepoint name */
{
	trx_named_savept_t*	savep;

	ut_ad(trx_state_eq(trx, TRX_STATE_ACTIVE));
	ut_ad(trx->in_mysql_trx_list);

	savep = trx_savepoint_find(trx, savepoint_name);

	if (savep != NULL) {
		trx_roll_savepoint_free(trx, savep);
	}

	return(savep != NULL ? DB_SUCCESS : DB_NO_SAVEPOINT);
}

/*******************************************************************//**
Determines if this transaction is rolling back an incomplete transaction
in crash recovery.
@return TRUE if trx is an incomplete transaction that is being rolled
back in crash recovery */
UNIV_INTERN
ibool
trx_is_recv(
/*========*/
	const trx_t*	trx)	/*!< in: transaction */
{
	return(trx == trx_roll_crash_recv_trx);
}

/*******************************************************************//**
Returns a transaction savepoint taken at this point in time.
@return	savepoint */
UNIV_INTERN
trx_savept_t
trx_savept_take(
/*============*/
	trx_t*	trx)	/*!< in: transaction */
{
	trx_savept_t	savept;

	savept.least_undo_no = trx->undo_no;

	return(savept);
}

/*******************************************************************//**
Roll back an active transaction. */
static
void
trx_rollback_active(
/*================*/
	trx_t*	trx)	/*!< in/out: transaction */
{
	mem_heap_t*	heap;
	que_fork_t*	fork;
	que_thr_t*	thr;
	roll_node_t*	roll_node;
	dict_table_t*	table;
	ib_int64_t	rows_to_undo;
	const char*	unit		= "";
	ibool		dictionary_locked = FALSE;

	heap = mem_heap_create(512);

	fork = que_fork_create(NULL, NULL, QUE_FORK_RECOVERY, heap);
	fork->trx = trx;

	thr = que_thr_create(fork, heap);

	roll_node = roll_node_create(heap);

	thr->child = roll_node;
	roll_node->common.parent = thr;

	trx->graph = fork;

	ut_a(thr == que_fork_start_command(fork));

	mutex_enter(&trx_sys->mutex);

	trx_roll_crash_recv_trx	= trx;

	trx_roll_max_undo_no = trx->undo_no;

	trx_roll_progress_printed_pct = 0;

	rows_to_undo = trx_roll_max_undo_no;

	mutex_exit(&trx_sys->mutex);

	if (rows_to_undo > 1000000000) {
		rows_to_undo = rows_to_undo / 1000000;
		unit = "M";
	}

	ut_print_timestamp(stderr);
	fprintf(stderr,
		"  InnoDB: Rolling back trx with id " TRX_ID_FMT ", %lu%s"
		" rows to undo\n",
		trx->id,
		(ulong) rows_to_undo, unit);

	if (trx_get_dict_operation(trx) != TRX_DICT_OP_NONE) {
		row_mysql_lock_data_dictionary(trx);
		dictionary_locked = TRUE;
	}

	que_run_threads(thr);
	ut_a(roll_node->undo_thr != NULL);

	que_run_threads(roll_node->undo_thr);

	trx_rollback_finish(thr_get_trx(roll_node->undo_thr));

	/* Free the memory reserved by the undo graph */
	que_graph_free(static_cast<que_t*>(
			       roll_node->undo_thr->common.parent));

	ut_a(trx->lock.que_state == TRX_QUE_RUNNING);

	if (trx_get_dict_operation(trx) != TRX_DICT_OP_NONE
	    && trx->table_id != 0) {

		/* If the transaction was for a dictionary operation,
		we drop the relevant table only if it is not flagged
		as DISCARDED. If it still exists. */

		table = dict_table_open_on_id(
			trx->table_id, dictionary_locked,
			DICT_TABLE_OP_NORMAL);

		if (table && !dict_table_is_discarded(table)) {

			dberr_t	err;

			/* Ensure that the table doesn't get evicted from the
			cache, keeps things simple for drop. */

			if (table->can_be_evicted) {
				dict_table_move_from_lru_to_non_lru(table);
			}

			dict_table_close(table, dictionary_locked, FALSE);

			ib_logf(IB_LOG_LEVEL_WARN,
				"Dropping table '%s', with id " UINT64PF " "
				"in recovery",
				table->name, trx->table_id);

			err = row_drop_table_for_mysql(table->name, trx, TRUE);
			trx_commit_for_mysql(trx);

			ut_a(err == DB_SUCCESS);
		}
	}

	if (dictionary_locked) {
		row_mysql_unlock_data_dictionary(trx);
	}

	ib_logf(IB_LOG_LEVEL_INFO,
		"Rollback of trx with id " TRX_ID_FMT " completed", trx->id);

	mem_heap_free(heap);

	trx_roll_crash_recv_trx	= NULL;
}

/*******************************************************************//**
Rollback or clean up any resurrected incomplete transactions. It assumes
that the caller holds the trx_sys_t::mutex and it will release the
lock if it does a clean up or rollback.
@return TRUE if the transaction was cleaned up or rolled back
and trx_sys->mutex was released. */
static
ibool
trx_rollback_resurrected(
/*=====================*/
	trx_t*	trx,	/*!< in: transaction to rollback or clean */
	ibool	all)	/*!< in: FALSE=roll back dictionary transactions;
			TRUE=roll back all non-PREPARED transactions */
{
	ut_ad(mutex_own(&trx_sys->mutex));

	/* The trx->is_recovered flag and trx->state are set
	atomically under the protection of the trx->mutex (and
	lock_sys->mutex) in lock_trx_release_locks(). We do not want
	to accidentally clean up a non-recovered transaction here. */

	trx_mutex_enter(trx);
	bool		is_recovered	= trx->is_recovered;
	trx_state_t	state		= trx->state;
	trx_mutex_exit(trx);

	if (!is_recovered) {
		return(FALSE);
	}

	switch (state) {
	case TRX_STATE_COMMITTED_IN_MEMORY:
		mutex_exit(&trx_sys->mutex);
		fprintf(stderr,
			"InnoDB: Cleaning up trx with id " TRX_ID_FMT "\n",
			trx->id);
		trx_cleanup_at_db_startup(trx);
		trx_free_for_background(trx);
		return(TRUE);
	case TRX_STATE_ACTIVE:
		if (all || trx_get_dict_operation(trx) != TRX_DICT_OP_NONE) {
			mutex_exit(&trx_sys->mutex);
			trx_rollback_active(trx);
			trx_free_for_background(trx);
			return(TRUE);
		}
		return(FALSE);
	case TRX_STATE_PREPARED:
		return(FALSE);
	case TRX_STATE_NOT_STARTED:
		break;
	}

	ut_error;
	return(FALSE);
}

/*******************************************************************//**
Rollback or clean up any incomplete transactions which were
encountered in crash recovery.  If the transaction already was
committed, then we clean up a possible insert undo log. If the
transaction was not yet committed, then we roll it back. */
UNIV_INTERN
void
trx_rollback_or_clean_recovered(
/*============================*/
	ibool	all)	/*!< in: FALSE=roll back dictionary transactions;
			TRUE=roll back all non-PREPARED transactions */
{
	trx_t*	trx;

	ut_a(srv_force_recovery < SRV_FORCE_NO_TRX_UNDO);

	if (trx_sys_get_n_rw_trx() == 0) {

		return;
	}

	if (all) {
		fprintf(stderr,
			"InnoDB: Starting in background the rollback"
			" of uncommitted transactions\n");
	}

	/* Note: For XA recovered transactions, we rely on MySQL to
	do rollback. They will be in TRX_STATE_PREPARED state. If the server
	is shutdown and they are still lingering in trx_sys_t::trx_list
	then the shutdown will hang. */

	/* Loop over the transaction list as long as there are
	recovered transactions to clean up or recover. */

	do {
		mutex_enter(&trx_sys->mutex);

		for (trx = UT_LIST_GET_FIRST(trx_sys->rw_trx_list);
		     trx != NULL;
		     trx = UT_LIST_GET_NEXT(trx_list, trx)) {

			assert_trx_in_rw_list(trx);

			/* If this function does a cleanup or rollback
			then it will release the trx_sys->mutex, therefore
			we need to reacquire it before retrying the loop. */

			if (trx_rollback_resurrected(trx, all)) {

				mutex_enter(&trx_sys->mutex);

				break;
			}
		}

		mutex_exit(&trx_sys->mutex);

	} while (trx != NULL);

	if (all) {
		ut_print_timestamp(stderr);
		fprintf(stderr,
			"  InnoDB: Rollback of non-prepared"
			" transactions completed\n");
	}
}

/*******************************************************************//**
Rollback or clean up any incomplete transactions which were
encountered in crash recovery.  If the transaction already was
committed, then we clean up a possible insert undo log. If the
transaction was not yet committed, then we roll it back.
Note: this is done in a background thread.
@return	a dummy parameter */
extern "C" UNIV_INTERN
os_thread_ret_t
DECLARE_THREAD(trx_rollback_or_clean_all_recovered)(
/*================================================*/
	void*	arg __attribute__((unused)))
			/*!< in: a dummy parameter required by
			os_thread_create */
{
	ut_ad(!srv_read_only_mode);

#ifdef UNIV_PFS_THREAD
	pfs_register_thread(trx_rollback_clean_thread_key);
#endif /* UNIV_PFS_THREAD */

	trx_rollback_or_clean_recovered(TRUE);

	/* We count the number of threads in os_thread_exit(). A created
	thread should always use that to exit and not use return() to exit. */

	os_thread_exit(NULL);

	OS_THREAD_DUMMY_RETURN;
}

/*******************************************************************//**
Creates an undo number array.
@return	own: undo number array */
static
trx_undo_arr_t*
trx_undo_arr_create(
/*================*/
	ulint		n_cells)	/*!< Number of cells */
{
	trx_undo_arr_t*	arr;
	mem_heap_t*	heap;
	ulint		sz = sizeof(*arr) + sizeof(*arr->infos) * n_cells;

	heap = mem_heap_create(sz);

	arr = static_cast<trx_undo_arr_t*>(mem_heap_zalloc(heap, sz));

	arr->n_cells = n_cells;

	arr->infos = (trx_undo_inf_t*) (arr + 1);

	arr->heap = heap;

	return(arr);
}

/*******************************************************************//**
Frees an undo number array. */
UNIV_INTERN
void
trx_undo_arr_free(
/*==============*/
	trx_undo_arr_t*	arr)	/*!< in: undo number array */
{
	mem_heap_free(arr->heap);
}

/*******************************************************************//**
Stores info of an undo log record to the array if it is not stored yet.
@return	FALSE if the record already existed in the array */
static
ibool
trx_undo_arr_store_info(
/*====================*/
	trx_t*		trx,	/*!< in: transaction */
	undo_no_t	undo_no)/*!< in: undo number */
{
	ulint		i;
	trx_undo_arr_t*	arr;
	ulint		n = 0;
	ulint		n_used;
	trx_undo_inf_t*	stored_here = NULL;

	arr = trx->undo_no_arr;
	n_used = arr->n_used;

	for (i = 0; i < arr->n_cells; i++) {
		trx_undo_inf_t*	cell;

		cell = trx_undo_arr_get_nth_info(arr, i);

		if (!cell->in_use) {
			if (!stored_here) {
				/* Not in use, we may store here */
				cell->undo_no = undo_no;
				cell->in_use = TRUE;

				arr->n_used++;

				stored_here = cell;
			}
		} else {
			n++;

			if (cell->undo_no == undo_no) {

				if (stored_here) {
					stored_here->in_use = FALSE;
					ut_ad(arr->n_used > 0);
					arr->n_used--;
				}

				ut_ad(arr->n_used == n_used);

				return(FALSE);
			}
		}

		if (n == n_used && stored_here) {

			ut_ad(arr->n_used == 1 + n_used);

			return(TRUE);
		}
	}

	ut_error;

	return(FALSE);
}

/*******************************************************************//**
Removes an undo number from the array. */
static
void
trx_undo_arr_remove_info(
/*=====================*/
	trx_undo_arr_t*	arr,	/*!< in: undo number array */
	undo_no_t	undo_no)/*!< in: undo number */
{
	ulint		i;

	for (i = 0; i < arr->n_cells; i++) {

		trx_undo_inf_t*	cell;

		cell = trx_undo_arr_get_nth_info(arr, i);

		if (cell->in_use && cell->undo_no == undo_no) {
			cell->in_use = FALSE;
			ut_ad(arr->n_used > 0);
			--arr->n_used;
			break;
		}
	}
}

/*******************************************************************//**
Gets the biggest undo number in an array.
@return	biggest value, 0 if the array is empty */
static
undo_no_t
trx_undo_arr_get_biggest(
/*=====================*/
	const trx_undo_arr_t*	arr)	/*!< in: undo number array */
{
	ulint		i;
	undo_no_t	biggest = 0;
	ulint		n_checked = 0;

	for (i = 0; i < arr->n_cells && n_checked < arr->n_used; ++i) {

		const trx_undo_inf_t*	cell = &arr->infos[i];

		if (cell->in_use) {

			++n_checked;

			if (cell->undo_no > biggest) {

				biggest = cell->undo_no;
			}
		}
	}

	return(biggest);
}

/***********************************************************************//**
Tries truncate the undo logs. */
static
void
trx_roll_try_truncate(
/*==================*/
	trx_t*	trx)	/*!< in/out: transaction */
{
	undo_no_t		limit;
	const trx_undo_arr_t*	arr;

	ut_ad(mutex_own(&(trx->undo_mutex)));
	ut_ad(mutex_own(&((trx->rseg)->mutex)));

	trx->pages_undone = 0;

	arr = trx->undo_no_arr;

	limit = trx->undo_no;

	if (arr->n_used > 0) {
		undo_no_t	biggest;

		biggest = trx_undo_arr_get_biggest(arr);

		if (biggest >= limit) {

			limit = biggest + 1;
		}
	}

	if (trx->insert_undo) {
		trx_undo_truncate_end(trx, trx->insert_undo, limit);
	}

	if (trx->update_undo) {
		trx_undo_truncate_end(trx, trx->update_undo, limit);
	}
}

/***********************************************************************//**
Pops the topmost undo log record in a single undo log and updates the info
about the topmost record in the undo log memory struct.
@return	undo log record, the page s-latched */
static
trx_undo_rec_t*
trx_roll_pop_top_rec(
/*=================*/
	trx_t*		trx,	/*!< in: transaction */
	trx_undo_t*	undo,	/*!< in: undo log */
	mtr_t*		mtr)	/*!< in: mtr */
{
	page_t*		undo_page;
	ulint		offset;
	trx_undo_rec_t*	prev_rec;
	page_t*		prev_rec_page;

	ut_ad(mutex_own(&trx->undo_mutex));

	undo_page = trx_undo_page_get_s_latched(
		undo->space, undo->zip_size, undo->top_page_no, mtr);

	offset = undo->top_offset;

	/*	fprintf(stderr, "Thread %lu undoing trx " TRX_ID_FMT
			" undo record " TRX_ID_FMT "\n",
	os_thread_get_curr_id(), trx->id, undo->top_undo_no); */

	prev_rec = trx_undo_get_prev_rec(
		undo_page + offset, undo->hdr_page_no, undo->hdr_offset,
		true, mtr);

	if (prev_rec == NULL) {

		undo->empty = TRUE;
	} else {
		prev_rec_page = page_align(prev_rec);

		if (prev_rec_page != undo_page) {

			trx->pages_undone++;
		}

		undo->top_page_no = page_get_page_no(prev_rec_page);
		undo->top_offset  = prev_rec - prev_rec_page;
		undo->top_undo_no = trx_undo_rec_get_undo_no(prev_rec);
	}

	return(undo_page + offset);
}

/********************************************************************//**
Pops the topmost record when the two undo logs of a transaction are seen
as a single stack of records ordered by their undo numbers. Inserts the
undo number of the popped undo record to the array of currently processed
undo numbers in the transaction. When the query thread finishes processing
of this undo record, it must be released with trx_undo_rec_release.
@return undo log record copied to heap, NULL if none left, or if the
undo number of the top record would be less than the limit */
UNIV_INTERN
trx_undo_rec_t*
trx_roll_pop_top_rec_of_trx(
/*========================*/
	trx_t*		trx,	/*!< in: transaction */
	undo_no_t	limit,	/*!< in: least undo number we need */
	roll_ptr_t*	roll_ptr,/*!< out: roll pointer to undo record */
	mem_heap_t*	heap)	/*!< in: memory heap where copied */
{
	trx_undo_t*	undo;
	trx_undo_t*	ins_undo;
	trx_undo_t*	upd_undo;
	trx_undo_rec_t*	undo_rec;
	trx_undo_rec_t*	undo_rec_copy;
	undo_no_t	undo_no;
	ibool		is_insert;
	trx_rseg_t*	rseg;
	ulint		progress_pct;
	mtr_t		mtr;

	rseg = trx->rseg;
try_again:
	mutex_enter(&(trx->undo_mutex));

	if (trx->pages_undone >= TRX_ROLL_TRUNC_THRESHOLD) {
		mutex_enter(&rseg->mutex);

		trx_roll_try_truncate(trx);

		mutex_exit(&rseg->mutex);
	}

	ins_undo = trx->insert_undo;
	upd_undo = trx->update_undo;

	if (!ins_undo || ins_undo->empty) {
		undo = upd_undo;
	} else if (!upd_undo || upd_undo->empty) {
		undo = ins_undo;
	} else if (upd_undo->top_undo_no > ins_undo->top_undo_no) {
		undo = upd_undo;
	} else {
		undo = ins_undo;
	}

	if (!undo || undo->empty || limit > undo->top_undo_no) {

		if ((trx->undo_no_arr)->n_used == 0) {
			/* Rollback is ending */

			mutex_enter(&(rseg->mutex));

			trx_roll_try_truncate(trx);

			mutex_exit(&(rseg->mutex));
		}

		mutex_exit(&(trx->undo_mutex));

		return(NULL);
	}

	is_insert = (undo == ins_undo);

	*roll_ptr = trx_undo_build_roll_ptr(
		is_insert, undo->rseg->id, undo->top_page_no, undo->top_offset);

	mtr_start(&mtr);

	undo_rec = trx_roll_pop_top_rec(trx, undo, &mtr);

	undo_no = trx_undo_rec_get_undo_no(undo_rec);

	ut_ad(undo_no + 1 == trx->undo_no);

	/* We print rollback progress info if we are in a crash recovery
	and the transaction has at least 1000 row operations to undo. */

	if (trx == trx_roll_crash_recv_trx && trx_roll_max_undo_no > 1000) {

		progress_pct = 100 - (ulint)
			((undo_no * 100) / trx_roll_max_undo_no);
		if (progress_pct != trx_roll_progress_printed_pct) {
			if (trx_roll_progress_printed_pct == 0) {
				fprintf(stderr,
					"\nInnoDB: Progress in percents:"
					" %lu", (ulong) progress_pct);
			} else {
				fprintf(stderr,
					" %lu", (ulong) progress_pct);
			}
			fflush(stderr);
			trx_roll_progress_printed_pct = progress_pct;
		}
	}

	trx->undo_no = undo_no;

	if (!trx_undo_arr_store_info(trx, undo_no)) {
		/* A query thread is already processing this undo log record */

		mutex_exit(&(trx->undo_mutex));

		mtr_commit(&mtr);

		goto try_again;
	}

	undo_rec_copy = trx_undo_rec_copy(undo_rec, heap);

	mutex_exit(&(trx->undo_mutex));

	mtr_commit(&mtr);

	return(undo_rec_copy);
}

/********************************************************************//**
Reserves an undo log record for a query thread to undo. This should be
called if the query thread gets the undo log record not using the pop
function above.
@return	TRUE if succeeded */
UNIV_INTERN
ibool
trx_undo_rec_reserve(
/*=================*/
	trx_t*		trx,	/*!< in/out: transaction */
	undo_no_t	undo_no)/*!< in: undo number of the record */
{
	ibool	ret;

	mutex_enter(&(trx->undo_mutex));

	ret = trx_undo_arr_store_info(trx, undo_no);

	mutex_exit(&(trx->undo_mutex));

	return(ret);
}

/*******************************************************************//**
Releases a reserved undo record. */
UNIV_INTERN
void
trx_undo_rec_release(
/*=================*/
	trx_t*		trx,	/*!< in/out: transaction */
	undo_no_t	undo_no)/*!< in: undo number */
{
	trx_undo_arr_t*	arr;

	mutex_enter(&(trx->undo_mutex));

	arr = trx->undo_no_arr;

	trx_undo_arr_remove_info(arr, undo_no);

	mutex_exit(&(trx->undo_mutex));
}

/****************************************************************//**
Builds an undo 'query' graph for a transaction. The actual rollback is
performed by executing this query graph like a query subprocedure call.
The reply about the completion of the rollback will be sent by this
graph.
@return	own: the query graph */
static
que_t*
trx_roll_graph_build(
/*=================*/
	trx_t*	trx)	/*!< in: trx handle */
{
	mem_heap_t*	heap;
	que_fork_t*	fork;
	que_thr_t*	thr;

	ut_ad(trx_mutex_own(trx));

	heap = mem_heap_create(512);
	fork = que_fork_create(NULL, NULL, QUE_FORK_ROLLBACK, heap);
	fork->trx = trx;

	thr = que_thr_create(fork, heap);

	thr->child = row_undo_node_create(trx, thr, heap);

	return(fork);
}

/*********************************************************************//**
Starts a rollback operation, creates the UNDO graph that will do the
actual undo operation.
@return query graph thread that will perform the UNDO operations. */
static
que_thr_t*
trx_rollback_start(
/*===============*/
	trx_t*		trx,		/*!< in: transaction */
	ib_id_t		roll_limit)	/*!< in: rollback to undo no (for
					partial undo), 0 if we are rolling back
					the entire transaction */
{
	que_t*		roll_graph;

	ut_ad(trx_mutex_own(trx));

	ut_ad(trx->undo_no_arr == NULL || trx->undo_no_arr->n_used == 0);

	/* Initialize the rollback field in the transaction */

	trx->roll_limit = roll_limit;

	ut_a(trx->roll_limit <= trx->undo_no);

	trx->pages_undone = 0;

	if (trx->undo_no_arr == NULL) {
		/* Single query thread -> 1 */
		trx->undo_no_arr = trx_undo_arr_create(1);
	}

	/* Build a 'query' graph which will perform the undo operations */

	roll_graph = trx_roll_graph_build(trx);

	trx->graph = roll_graph;

	trx->lock.que_state = TRX_QUE_ROLLING_BACK;

	return(que_fork_start_command(roll_graph));
}

/****************************************************************//**
Finishes a transaction rollback. */
static
void
trx_rollback_finish(
/*================*/
	trx_t*		trx)	/*!< in: transaction */
{
	ut_a(trx->undo_no_arr == NULL || trx->undo_no_arr->n_used == 0);

	trx_commit(trx);

	trx->lock.que_state = TRX_QUE_RUNNING;
}

/*********************************************************************//**
Creates a rollback command node struct.
@return	own: rollback node struct */
UNIV_INTERN
roll_node_t*
roll_node_create(
/*=============*/
	mem_heap_t*	heap)	/*!< in: mem heap where created */
{
	roll_node_t*	node;

	node = static_cast<roll_node_t*>(mem_heap_zalloc(heap, sizeof(*node)));

	node->state = ROLL_NODE_SEND;

	node->common.type = QUE_NODE_ROLLBACK;

	return(node);
}

/***********************************************************//**
Performs an execution step for a rollback command node in a query graph.
@return	query thread to run next, or NULL */
UNIV_INTERN
que_thr_t*
trx_rollback_step(
/*==============*/
	que_thr_t*	thr)	/*!< in: query thread */
{
	roll_node_t*	node;

	node = static_cast<roll_node_t*>(thr->run_node);

	ut_ad(que_node_get_type(node) == QUE_NODE_ROLLBACK);

	if (thr->prev_node == que_node_get_parent(node)) {
		node->state = ROLL_NODE_SEND;
	}

	if (node->state == ROLL_NODE_SEND) {
		trx_t*		trx;
		ib_id_t		roll_limit = 0;

		trx = thr_get_trx(thr);

		trx_mutex_enter(trx);

		node->state = ROLL_NODE_WAIT;

		ut_a(node->undo_thr == NULL);

		roll_limit = node->partial ? node->savept.least_undo_no : 0;

		trx_commit_or_rollback_prepare(trx);

		node->undo_thr = trx_rollback_start(trx, roll_limit);

		trx_mutex_exit(trx);

	} else {
		ut_ad(node->state == ROLL_NODE_WAIT);

		thr->run_node = que_node_get_parent(node);
	}

	return(thr);
}