mariadb/storage/innobase/trx/trx0rseg.cc

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

Copyright (c) 1996, 2016, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2017, 2023, MariaDB Corporation.

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
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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.,
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*****************************************************************************/

/**************************************************//**
@file trx/trx0rseg.cc
Rollback segment

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

#include "trx0rseg.h"
#include "trx0undo.h"
#include "fut0lst.h"
#include "srv0srv.h"
#include "trx0purge.h"
#include "srv0mon.h"
#include "log.h"

#ifdef WITH_WSREP
# include <mysql/service_wsrep.h>

/** The offset to WSREP XID headers, after TRX_RSEG */
# define TRX_RSEG_WSREP_XID_INFO      TRX_RSEG_MAX_TRX_ID + 16 + 512

/** WSREP XID format (1 if present and valid, 0 if not present) */
# define TRX_RSEG_WSREP_XID_FORMAT    TRX_RSEG_WSREP_XID_INFO
/** WSREP XID GTRID length */
# define TRX_RSEG_WSREP_XID_GTRID_LEN TRX_RSEG_WSREP_XID_INFO + 4
/** WSREP XID bqual length */
# define TRX_RSEG_WSREP_XID_BQUAL_LEN TRX_RSEG_WSREP_XID_INFO + 8
/** WSREP XID data (XIDDATASIZE bytes) */
# define TRX_RSEG_WSREP_XID_DATA      TRX_RSEG_WSREP_XID_INFO + 12

# ifdef UNIV_DEBUG
/** The latest known WSREP XID sequence number */
static long long wsrep_seqno = -1;
# endif /* UNIV_DEBUG */
/** The latest known WSREP XID UUID */
static unsigned char wsrep_uuid[16];

/** Write the WSREP XID information into rollback segment header.
@param[in,out]	rseg_header	rollback segment header
@param[in]	xid		WSREP XID
@param[in,out]	mtr		mini transaction */
static void
trx_rseg_write_wsrep_checkpoint(
	buf_block_t*	rseg_header,
	const XID*	xid,
	mtr_t*		mtr)
{
	DBUG_ASSERT(xid->gtrid_length >= 0);
	DBUG_ASSERT(xid->bqual_length >= 0);
	DBUG_ASSERT(xid->gtrid_length + xid->bqual_length < XIDDATASIZE);

	mtr->write<4,mtr_t::MAYBE_NOP>(*rseg_header,
				       TRX_RSEG + TRX_RSEG_WSREP_XID_FORMAT
				       + rseg_header->page.frame,
				       uint32_t(xid->formatID));

	mtr->write<4,mtr_t::MAYBE_NOP>(*rseg_header,
				       TRX_RSEG + TRX_RSEG_WSREP_XID_GTRID_LEN
				       + rseg_header->page.frame,
				       uint32_t(xid->gtrid_length));

	mtr->write<4,mtr_t::MAYBE_NOP>(*rseg_header,
				       TRX_RSEG + TRX_RSEG_WSREP_XID_BQUAL_LEN
				       + rseg_header->page.frame,
				       uint32_t(xid->bqual_length));

	const ulint xid_length = static_cast<ulint>(xid->gtrid_length
						    + xid->bqual_length);
	mtr->memcpy<mtr_t::MAYBE_NOP>(*rseg_header,
				      TRX_RSEG + TRX_RSEG_WSREP_XID_DATA
				      + rseg_header->page.frame,
				      xid->data, xid_length);
	if (xid_length < XIDDATASIZE
	    && memcmp(TRX_RSEG + TRX_RSEG_WSREP_XID_DATA
		      + rseg_header->page.frame, field_ref_zero,
		      XIDDATASIZE - xid_length)) {
		mtr->memset(rseg_header,
			    TRX_RSEG + TRX_RSEG_WSREP_XID_DATA + xid_length,
			    XIDDATASIZE - xid_length, 0);
	}
}

/** Update the WSREP XID information in rollback segment header.
@param[in,out]	rseg_header	rollback segment header
@param[in]	xid		WSREP XID
@param[in,out]	mtr		mini-transaction */
void
trx_rseg_update_wsrep_checkpoint(
	buf_block_t*	rseg_header,
	const XID*	xid,
	mtr_t*		mtr)
{
	ut_ad(wsrep_is_wsrep_xid(xid));

#ifdef UNIV_DEBUG
	/* Check that seqno is monotonically increasing */
	long long xid_seqno = wsrep_xid_seqno(xid);
	const byte* xid_uuid = wsrep_xid_uuid(xid);

	if (xid_seqno != -1
	    && !memcmp(xid_uuid, wsrep_uuid, sizeof wsrep_uuid)) {
		ut_ad(xid_seqno > wsrep_seqno);
	} else {
		memcpy(wsrep_uuid, xid_uuid, sizeof wsrep_uuid);
	}
	wsrep_seqno = xid_seqno;
#endif /* UNIV_DEBUG */
	trx_rseg_write_wsrep_checkpoint(rseg_header, xid, mtr);
}

static dberr_t trx_rseg_update_wsrep_checkpoint(const XID* xid, mtr_t* mtr)
{
  dberr_t err;
  buf_block_t *rseg_header = trx_sys.rseg_array[0].get(mtr, &err);

  if (UNIV_UNLIKELY(!rseg_header))
    return err;

  /* We must make check against wsrep_uuid here, the
  trx_rseg_update_wsrep_checkpoint() writes over wsrep_uuid with xid
  contents in debug mode and the memcmp() will never give nonzero
  result. */
  const bool must_clear_rsegs=
    memcmp(wsrep_uuid, wsrep_xid_uuid(xid), sizeof wsrep_uuid);

  if (UNIV_UNLIKELY(mach_read_from_4(TRX_RSEG + TRX_RSEG_FORMAT +
                                     rseg_header->page.frame)))
    trx_rseg_format_upgrade(rseg_header, mtr);

  trx_rseg_update_wsrep_checkpoint(rseg_header, xid, mtr);

  if (must_clear_rsegs)
    /* Because the UUID part of the WSREP XID differed from
    current_xid_uuid, the WSREP group UUID was changed, and we must
    reset the XID in all rollback segment headers. */
    for (ulint rseg_id= 1; rseg_id < TRX_SYS_N_RSEGS; ++rseg_id)
      if (buf_block_t* block= trx_sys.rseg_array[rseg_id].get(mtr, &err))
        mtr->memset(block, TRX_RSEG + TRX_RSEG_WSREP_XID_INFO,
                    TRX_RSEG_WSREP_XID_DATA + XIDDATASIZE -
                    TRX_RSEG_WSREP_XID_INFO, 0);
  return err;
}

/** Update WSREP checkpoint XID in first rollback segment header
as part of wsrep_set_SE_checkpoint() when it is guaranteed that there
are no wsrep transactions committing.
If the UUID part of the WSREP XID does not match to the UUIDs of XIDs already
stored into rollback segments, the WSREP XID in all the remaining rollback
segments will be reset.
@param[in]	xid		WSREP XID */
void trx_rseg_update_wsrep_checkpoint(const XID* xid)
{
	mtr_t	mtr;
	mtr.start();
	trx_rseg_update_wsrep_checkpoint(xid, &mtr);
	mtr.commit();
}

/** Read the WSREP XID information in rollback segment header.
@param[in]	rseg_header	Rollback segment header
@param[out]	xid		Transaction XID
@return	whether the WSREP XID was present */
static
bool trx_rseg_read_wsrep_checkpoint(const buf_block_t *rseg_header, XID &xid)
{
	int formatID = static_cast<int>(
		mach_read_from_4(TRX_RSEG + TRX_RSEG_WSREP_XID_FORMAT
				 + rseg_header->page.frame));
	if (formatID == 0) {
		return false;
	}

	xid.formatID = formatID;
	xid.gtrid_length = static_cast<int>(
		mach_read_from_4(TRX_RSEG + TRX_RSEG_WSREP_XID_GTRID_LEN
				 + rseg_header->page.frame));

	xid.bqual_length = static_cast<int>(
		mach_read_from_4(TRX_RSEG + TRX_RSEG_WSREP_XID_BQUAL_LEN
				 + rseg_header->page.frame));

	memcpy(xid.data, TRX_RSEG + TRX_RSEG_WSREP_XID_DATA
	       + rseg_header->page.frame, XIDDATASIZE);

	return wsrep_is_wsrep_xid(&xid);
}

/** Read the WSREP XID from the TRX_SYS page (in case of upgrade).
@param[in]	page	TRX_SYS page
@param[out]	xid	WSREP XID (if present)
@return	whether the WSREP XID is present */
static bool trx_rseg_init_wsrep_xid(const page_t* page, XID& xid)
{
	if (memcmp(TRX_SYS + TRX_SYS_WSREP_XID_INFO + page,
		           field_ref_zero, TRX_SYS_WSREP_XID_LEN) == 0) {
		return false;
	}

	if (mach_read_from_4(TRX_SYS + TRX_SYS_WSREP_XID_INFO
			     + TRX_SYS_WSREP_XID_MAGIC_N_FLD
			     + page)
	    != TRX_SYS_WSREP_XID_MAGIC_N) {
		return false;
	}

	xid.formatID = static_cast<int>(
		mach_read_from_4(
			TRX_SYS + TRX_SYS_WSREP_XID_INFO
			+ TRX_SYS_WSREP_XID_FORMAT + page));
	xid.gtrid_length = static_cast<int>(
		mach_read_from_4(
			TRX_SYS + TRX_SYS_WSREP_XID_INFO
			+ TRX_SYS_WSREP_XID_GTRID_LEN + page));
	xid.bqual_length = static_cast<int>(
		mach_read_from_4(
			TRX_SYS + TRX_SYS_WSREP_XID_INFO
			+ TRX_SYS_WSREP_XID_BQUAL_LEN + page));
	memcpy(xid.data,
	       TRX_SYS + TRX_SYS_WSREP_XID_INFO
	       + TRX_SYS_WSREP_XID_DATA + page, XIDDATASIZE);

	return wsrep_is_wsrep_xid(&xid);
}

/** Recover the latest WSREP checkpoint XID.
@param[out]	xid	WSREP XID
@return	whether the WSREP XID was found */
bool trx_rseg_read_wsrep_checkpoint(XID& xid)
{
	mtr_t		mtr;
	long long       max_xid_seqno = -1;
	bool		found = false;

	for (ulint rseg_id = 0; rseg_id < TRX_SYS_N_RSEGS;
	     rseg_id++, mtr.commit()) {
		mtr.start();
		const buf_block_t* sys = trx_sysf_get(&mtr, false);
		if (UNIV_UNLIKELY(!sys)) {
			continue;
		}
		const uint32_t page_no = trx_sysf_rseg_get_page_no(
			sys, rseg_id);

		if (page_no == FIL_NULL) {
			continue;
		}

		const buf_block_t* rseg_header = buf_page_get_gen(
			page_id_t(trx_sysf_rseg_get_space(sys, rseg_id),
				  page_no),
			0, RW_S_LATCH, nullptr, BUF_GET, &mtr);

		if (!rseg_header) {
			continue;
		}

		if (mach_read_from_4(TRX_RSEG + TRX_RSEG_FORMAT
				     + rseg_header->page.frame)) {
			continue;
		}

		XID tmp_xid;
		long long tmp_seqno = 0;
		if (trx_rseg_read_wsrep_checkpoint(rseg_header, tmp_xid)
		    && (tmp_seqno = wsrep_xid_seqno(&tmp_xid))
		    > max_xid_seqno) {
			found = true;
			max_xid_seqno = tmp_seqno;
			xid = tmp_xid;
			memcpy(wsrep_uuid, wsrep_xid_uuid(&tmp_xid),
			       sizeof wsrep_uuid);
		}
	}

	return found;
}
#endif /* WITH_WSREP */

buf_block_t *trx_rseg_t::get(mtr_t *mtr, dberr_t *err) const
{
  if (!space)
  {
    if (err) *err= DB_TABLESPACE_NOT_FOUND;
    return nullptr;
  }

  buf_block_t *block= buf_page_get_gen(page_id(), 0, RW_X_LATCH, nullptr,
                                       BUF_GET, mtr, err);
  if (UNIV_LIKELY(block != nullptr))
    buf_page_make_young_if_needed(&block->page);

  return block;
}

/** Upgrade a rollback segment header page to MariaDB 10.3 format.
@param[in,out]	rseg_header	rollback segment header page
@param[in,out]	mtr		mini-transaction */
void trx_rseg_format_upgrade(buf_block_t *rseg_header, mtr_t *mtr)
{
  mtr->memset(rseg_header, TRX_RSEG + TRX_RSEG_FORMAT, 4, 0);
  /* Clear also possible garbage at the end of the page. Old
  InnoDB versions did not initialize unused parts of pages. */
  mtr->memset(rseg_header, TRX_RSEG + TRX_RSEG_MAX_TRX_ID + 8,
              srv_page_size
              - (FIL_PAGE_DATA_END + TRX_RSEG + TRX_RSEG_MAX_TRX_ID + 8),
              0);
}

/** Create a rollback segment header.
@param[in,out]  space           system, undo, or temporary tablespace
@param[in]      rseg_id         rollback segment identifier
@param[in]      max_trx_id      new value of TRX_RSEG_MAX_TRX_ID
@param[in,out]  mtr             mini-transaction
@param[out]     err             error code
@return the created rollback segment
@retval nullptr on failure */
buf_block_t *trx_rseg_header_create(fil_space_t *space, ulint rseg_id,
                                    trx_id_t max_trx_id, mtr_t *mtr,
                                    dberr_t *err)
{
  ut_ad(mtr->memo_contains(*space));
  buf_block_t *block=
    fseg_create(space, TRX_RSEG + TRX_RSEG_FSEG_HEADER, mtr, err);
  if (block)
  {
    ut_ad(0 == mach_read_from_4(TRX_RSEG_FORMAT + TRX_RSEG +
                                block->page.frame));
    ut_ad(0 == mach_read_from_4(TRX_RSEG_HISTORY_SIZE + TRX_RSEG +
                                block->page.frame));
    ut_ad(0 == mach_read_from_4(TRX_RSEG_MAX_TRX_ID + TRX_RSEG +
                                block->page.frame));

    /* Initialize the history list */
    flst_init(block, TRX_RSEG_HISTORY + TRX_RSEG, mtr);

    mtr->write<8,mtr_t::MAYBE_NOP>(*block, TRX_RSEG + TRX_RSEG_MAX_TRX_ID +
                                   block->page.frame, max_trx_id);

    /* Reset the undo log slots */
    mtr->memset(block, TRX_RSEG_UNDO_SLOTS + TRX_RSEG, TRX_RSEG_N_SLOTS * 4,
                0xff);
  }
  return block;
}

void trx_rseg_t::destroy()
{
  latch.destroy();

  /* There can't be any active transactions. */
  ut_a(!UT_LIST_GET_LEN(undo_list));

  for (trx_undo_t *next, *undo= UT_LIST_GET_FIRST(undo_cached); undo;
       undo= next)
  {
    next= UT_LIST_GET_NEXT(undo_list, undo);
    UT_LIST_REMOVE(undo_cached, undo);
    ut_free(undo);
  }
}

void trx_rseg_t::init(fil_space_t *space, uint32_t page)
{
  latch.SRW_LOCK_INIT(trx_rseg_latch_key);
  ut_ad(!this->space || this->space != space);
  this->space= space;
  page_no= page;
  last_page_no= FIL_NULL;
  curr_size= 1;

  UT_LIST_INIT(undo_list, &trx_undo_t::undo_list);
  UT_LIST_INIT(undo_cached, &trx_undo_t::undo_list);
}

void trx_rseg_t::reinit(uint32_t page)
{
  ut_ad(is_persistent());
  ut_ad(page_no == page);
  ut_a(!UT_LIST_GET_LEN(undo_list));
  ut_ad(!history_size || UT_LIST_GET_FIRST(undo_cached));

  history_size= 0;
  page_no= page;

  for (trx_undo_t *next, *undo= UT_LIST_GET_FIRST(undo_cached); undo;
       undo= next)
  {
    next= UT_LIST_GET_NEXT(undo_list, undo);
    UT_LIST_REMOVE(undo_cached, undo);
    ut_free(undo);
  }

  ut_ad(!is_referenced());
  needs_purge= 0;
  last_commit_and_offset= 0;
  last_page_no= FIL_NULL;
  curr_size= 1;
  ref.store(0, std::memory_order_release);
}

/** Read the undo log lists.
@param[in,out]  rseg            rollback segment
@param[in]      rseg_header     rollback segment header
@return error code */
static dberr_t trx_undo_lists_init(trx_rseg_t *rseg,
                                   const buf_block_t *rseg_header)
{
  ut_ad(srv_force_recovery < SRV_FORCE_NO_UNDO_LOG_SCAN);
  bool is_undo_empty= true;

  for (ulint i= 0; i < TRX_RSEG_N_SLOTS; i++)
  {
    uint32_t page_no= trx_rsegf_get_nth_undo(rseg_header, i);
    if (page_no != FIL_NULL)
    {
      const trx_undo_t *undo=
        trx_undo_mem_create_at_db_start(rseg, i, page_no);
      if (!undo)
        return DB_CORRUPTION;
      if (is_undo_empty)
        is_undo_empty= !undo->size || undo->state == TRX_UNDO_CACHED;
      rseg->curr_size+= undo->size;
    }
  }

  trx_sys.set_undo_non_empty(!is_undo_empty);
  return DB_SUCCESS;
}

/** Restore the state of a persistent rollback segment.
@param[in,out]	rseg		persistent rollback segment
@param[in,out]	mtr		mini-transaction
@return error code */
static dberr_t trx_rseg_mem_restore(trx_rseg_t *rseg, mtr_t *mtr)
{
  if (!rseg->space)
    return DB_TABLESPACE_NOT_FOUND;

  /* Access the tablespace header page to recover rseg->space->free_limit */
  page_id_t page_id{rseg->space->id, 0};
  dberr_t err;
  if (!buf_page_get_gen(page_id, 0, RW_X_LATCH, nullptr, BUF_GET, mtr, &err))
    return err;
  mtr->release_last_page();
  page_id.set_page_no(rseg->page_no);
  const buf_block_t *rseg_hdr=
    buf_page_get_gen(rseg->page_id(), 0, RW_X_LATCH, nullptr, BUF_GET, mtr,
                     &err);
  if (!rseg_hdr)
    return err;

  if (!mach_read_from_4(TRX_RSEG + TRX_RSEG_FORMAT + rseg_hdr->page.frame))
  {
    trx_id_t id= mach_read_from_8(TRX_RSEG + TRX_RSEG_MAX_TRX_ID +
                                  rseg_hdr->page.frame);

    if (id > rseg->needs_purge)
      rseg->needs_purge= id;

    const byte *binlog_name=
      TRX_RSEG + TRX_RSEG_BINLOG_NAME + rseg_hdr->page.frame;
    if (*binlog_name)
    {
      static_assert(TRX_RSEG_BINLOG_NAME_LEN ==
                    sizeof trx_sys.recovered_binlog_filename, "compatibility");

      /* Always prefer a position from rollback segment over
      a legacy position from before version 10.3.5. */
      int cmp= *trx_sys.recovered_binlog_filename &&
        !trx_sys.recovered_binlog_is_legacy_pos
        ? strncmp(reinterpret_cast<const char*>(binlog_name),
                  trx_sys.recovered_binlog_filename,
                  TRX_RSEG_BINLOG_NAME_LEN)
        : 1;

      if (cmp >= 0) {
        uint64_t binlog_offset =
          mach_read_from_8(TRX_RSEG + TRX_RSEG_BINLOG_OFFSET +
                           rseg_hdr->page.frame);
        if (cmp)
        {
          memcpy(trx_sys.recovered_binlog_filename, binlog_name,
                 TRX_RSEG_BINLOG_NAME_LEN);
          trx_sys.recovered_binlog_offset= binlog_offset;
        }
        else if (binlog_offset > trx_sys.recovered_binlog_offset)
          trx_sys.recovered_binlog_offset= binlog_offset;
        trx_sys.recovered_binlog_is_legacy_pos= false;
      }
    }
#ifdef WITH_WSREP
    XID tmp_xid;
    tmp_xid.null();
    /* Update recovered wsrep xid only if we found wsrep xid from
       rseg header page and read xid seqno is larger than currently
       recovered xid seqno. */
    if (trx_rseg_read_wsrep_checkpoint(rseg_hdr, tmp_xid) &&
        wsrep_xid_seqno(&tmp_xid) > wsrep_xid_seqno(&trx_sys.recovered_wsrep_xid))
      trx_sys.recovered_wsrep_xid.set(&tmp_xid);
#endif
  }

  if (srv_operation == SRV_OPERATION_RESTORE)
    /* mariabackup --prepare only deals with
    the redo log and the data files, not with
    transactions or the data dictionary. */
    return DB_SUCCESS;

  /* Initialize the undo log lists according to the rseg header */

  rseg->curr_size = mach_read_from_4(TRX_RSEG + TRX_RSEG_HISTORY_SIZE +
                                     rseg_hdr->page.frame) + 1;
  err= trx_undo_lists_init(rseg, rseg_hdr);
  if (err != DB_SUCCESS);
  else if (auto len= flst_get_len(TRX_RSEG + TRX_RSEG_HISTORY +
                                  rseg_hdr->page.frame))
  {
    rseg->history_size+= len;

    fil_addr_t node_addr= flst_get_last(TRX_RSEG + TRX_RSEG_HISTORY +
                                        rseg_hdr->page.frame);
    if (node_addr.page >= rseg->space->free_limit ||
        node_addr.boffset < TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_NODE ||
        node_addr.boffset >= srv_page_size - TRX_UNDO_LOG_OLD_HDR_SIZE)
      return DB_CORRUPTION;

    node_addr.boffset= static_cast<uint16_t>(node_addr.boffset -
                                             TRX_UNDO_HISTORY_NODE);
    rseg->last_page_no= node_addr.page;

    const buf_block_t* block=
      buf_page_get_gen(page_id_t(rseg->space->id, node_addr.page),
                       0, RW_S_LATCH, nullptr, BUF_GET, mtr, &err);
    if (!block)
      return err;

    trx_id_t id= mach_read_from_8(block->page.frame + node_addr.boffset +
                                  TRX_UNDO_TRX_ID);
    if (id > rseg->needs_purge)
      rseg->needs_purge= id;
    id= mach_read_from_8(block->page.frame + node_addr.boffset +
                         TRX_UNDO_TRX_NO);
    if (id > rseg->needs_purge)
      rseg->needs_purge= id;

    rseg->set_last_commit(node_addr.boffset, id);

    if (rseg->last_page_no != FIL_NULL)
      /* There is no need to cover this operation by the purge
      mutex because we are still bootstrapping. */
      purge_sys.enqueue(*rseg);
  }

  trx_sys.set_undo_non_empty(rseg->history_size > 0);
  return err;
}

/** Read binlog metadata from the TRX_SYS page, in case we are upgrading
from MySQL or a MariaDB version older than 10.3.5. */
static void trx_rseg_init_binlog_info(const page_t* page)
{
	if (mach_read_from_4(TRX_SYS + TRX_SYS_MYSQL_LOG_INFO
			     + TRX_SYS_MYSQL_LOG_MAGIC_N_FLD
			     + page)
	    == TRX_SYS_MYSQL_LOG_MAGIC_N) {
		memcpy(trx_sys.recovered_binlog_filename,
		       TRX_SYS_MYSQL_LOG_INFO + TRX_SYS_MYSQL_LOG_NAME
		       + TRX_SYS + page, TRX_SYS_MYSQL_LOG_NAME_LEN);
		trx_sys.recovered_binlog_offset = mach_read_from_8(
			TRX_SYS_MYSQL_LOG_INFO + TRX_SYS_MYSQL_LOG_OFFSET
			+ TRX_SYS + page);
		trx_sys.recovered_binlog_is_legacy_pos= true;
	}
}

/** Initialize or recover the rollback segments at startup. */
dberr_t trx_rseg_array_init()
{
	trx_id_t max_trx_id = 0;

	*trx_sys.recovered_binlog_filename = '\0';
	trx_sys.recovered_binlog_offset = 0;
	trx_sys.recovered_binlog_is_legacy_pos= false;
#ifdef WITH_WSREP
	trx_sys.recovered_wsrep_xid.null();
	XID wsrep_sys_xid;
	wsrep_sys_xid.null();
	bool wsrep_xid_in_rseg_found = false;
#endif
	mtr_t mtr;
	dberr_t err = DB_SUCCESS;
	/* mariabackup --prepare only deals with the redo log and the data
	files, not with	transactions or the data dictionary, that's why
	trx_lists_init_at_db_start() does not invoke purge_sys.create() and
	purge queue mutex stays uninitialized, and trx_rseg_mem_restore() quits
	before initializing undo log lists. */
	if (srv_operation != SRV_OPERATION_RESTORE)
		/* Acquiring purge queue mutex here should be fine from the
		deadlock prevention point of view, because executing that
		function is a prerequisite for starting the purge subsystem or
		any transactions. */
		purge_sys.queue_lock();
	for (ulint rseg_id = 0; rseg_id < TRX_SYS_N_RSEGS; rseg_id++) {
		mtr.start();
		if (const buf_block_t* sys = trx_sysf_get(&mtr, true)) {
			if (rseg_id == 0) {
				/* In case this is an upgrade from
				before MariaDB 10.3.5, fetch the base
				information from the TRX_SYS page. */
				max_trx_id = mach_read_from_8(
					TRX_SYS + TRX_SYS_TRX_ID_STORE
					+ sys->page.frame);
				trx_rseg_init_binlog_info(sys->page.frame);
#ifdef WITH_WSREP
				if (trx_rseg_init_wsrep_xid(
					    sys->page.frame, trx_sys.recovered_wsrep_xid)) {
					wsrep_sys_xid.set(
						&trx_sys.recovered_wsrep_xid);
				}
#endif
			}

			const uint32_t	page_no = trx_sysf_rseg_get_page_no(
				sys, rseg_id);
			if (page_no != FIL_NULL) {
				trx_rseg_t& rseg = trx_sys.rseg_array[rseg_id];
				uint32_t space_id=
					trx_sysf_rseg_get_space(
						sys, rseg_id);

				fil_space_t *rseg_space =
					fil_space_get(space_id);
				if (!rseg_space) {
					mtr.commit();
					err = DB_ERROR;
					sql_print_error(
					  "InnoDB: Failed to open the undo "
					  "tablespace undo%03" PRIu32,
					  (space_id -
					   srv_undo_space_id_start + 1));
					break;
				}

				rseg.destroy();
				rseg.init(rseg_space, page_no);
				ut_ad(rseg.is_persistent());
				err = trx_rseg_mem_restore(&rseg, &mtr);
				if (rseg.needs_purge > max_trx_id) {
					max_trx_id = rseg.needs_purge;
				}
				if (err != DB_SUCCESS) {
					mtr.commit();
					break;
				}
#ifdef WITH_WSREP
				if (!wsrep_sys_xid.is_null() &&
				    !wsrep_sys_xid.eq(&trx_sys.recovered_wsrep_xid)) {
					wsrep_xid_in_rseg_found = true;
					ut_ad(memcmp(wsrep_xid_uuid(&wsrep_sys_xid),
						     wsrep_xid_uuid(&trx_sys.recovered_wsrep_xid),
						     sizeof wsrep_uuid)
					      || wsrep_xid_seqno(
						      &wsrep_sys_xid)
					      <= wsrep_xid_seqno(
						      &trx_sys.recovered_wsrep_xid));
				}
#endif
			}
		}

		mtr.commit();
	}
	if (srv_operation != SRV_OPERATION_RESTORE)
		purge_sys.queue_unlock();
	if (err != DB_SUCCESS) {
		for (auto& rseg : trx_sys.rseg_array) {
			while (auto u = UT_LIST_GET_FIRST(rseg.undo_list)) {
				UT_LIST_REMOVE(rseg.undo_list, u);
				ut_free(u);
			}
		}
		return err;
	}

#ifdef WITH_WSREP
	if (srv_operation == SRV_OPERATION_NORMAL && !wsrep_sys_xid.is_null()) {
		/* Upgrade from a version prior to 10.3.5,
		where WSREP XID was stored in TRX_SYS page.
		If no rollback segment has a WSREP XID set,
		we must copy the XID found in TRX_SYS page
		to rollback segments. */
		mtr.start();

		if (!wsrep_xid_in_rseg_found) {
			trx_rseg_update_wsrep_checkpoint(&wsrep_sys_xid, &mtr);
		}

		/* Finally, clear WSREP XID in TRX_SYS page. */
		mtr.memset(trx_sysf_get(&mtr),
			   TRX_SYS + TRX_SYS_WSREP_XID_INFO,
			   TRX_SYS_WSREP_XID_LEN, 0);
		mtr.commit();
	}
#endif

	trx_sys.init_max_trx_id(max_trx_id + 1);
	return DB_SUCCESS;
}

/** Create the temporary rollback segments. */
dberr_t trx_temp_rseg_create(mtr_t *mtr)
{
  for (ulong i= 0; i < array_elements(trx_sys.temp_rsegs); i++)
  {
    mtr->start();
    mtr->set_log_mode(MTR_LOG_NO_REDO);
    mtr->x_lock_space(fil_system.temp_space);
    dberr_t err;
    buf_block_t *rblock=
      trx_rseg_header_create(fil_system.temp_space, i, 0, mtr, &err);
    if (UNIV_UNLIKELY(!rblock))
    {
      mtr->commit();
      return err;
    }
    trx_sys.temp_rsegs[i].destroy();
    trx_sys.temp_rsegs[i].init(fil_system.temp_space,
                               rblock->page.id().page_no());
    mtr->commit();
  }
  return DB_SUCCESS;
}

/** Update the offset information about the end of the binlog entry
which corresponds to the transaction just being committed.
In a replication slave, this updates the master binlog position
up to which replication has proceeded.
@param[in,out]	rseg_header	rollback segment header
@param[in]	log_file_name	binlog file name
@param[in]	log_offset	binlog file offset
@param[in,out]	mtr		mini-transaction */
void trx_rseg_update_binlog_offset(buf_block_t *rseg_header,
                                   const char *log_file_name,
                                   ulonglong log_offset,
                                   mtr_t *mtr)
{
  DBUG_PRINT("trx", ("trx_mysql_binlog_offset %llu", log_offset));
  const size_t len= strlen(log_file_name) + 1;
  ut_ad(len > 1);

  if (UNIV_UNLIKELY(len > TRX_RSEG_BINLOG_NAME_LEN))
    return;

  mtr->write<8,mtr_t::MAYBE_NOP>(
    *rseg_header,
    TRX_RSEG + TRX_RSEG_BINLOG_OFFSET + rseg_header->page.frame,
    log_offset);

  byte *name= TRX_RSEG + TRX_RSEG_BINLOG_NAME + rseg_header->page.frame;

  if (memcmp(log_file_name, name, len))
    mtr->memcpy(*rseg_header, name, log_file_name, len);
}