path: root/storage/innobase/include/trx0undo.h

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/**************************************************//**
@file include/trx0undo.h
Transaction undo log

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

#ifndef trx0undo_h
#define trx0undo_h

#ifndef UNIV_INNOCHECKSUM
#include "trx0sys.h"

/** The LSB of the "is insert" flag in DB_ROLL_PTR */
#define ROLL_PTR_INSERT_FLAG_POS 55
/** The LSB of the 7-bit trx_rseg_t::id in DB_ROLL_PTR */
#define ROLL_PTR_RSEG_ID_POS 48
/** The LSB of the 32-bit undo log page number in DB_ROLL_PTR */
#define ROLL_PTR_PAGE_POS 16
/** The LSB of the 16-bit byte offset within an undo log page in DB_ROLL_PTR */
#define ROLL_PTR_BYTE_POS 0

/***********************************************************************//**
Builds a roll pointer.
@return roll pointer */
UNIV_INLINE
roll_ptr_t
trx_undo_build_roll_ptr(
/*====================*/
	bool	is_insert,	/*!< in: TRUE if insert undo log */
	ulint	rseg_id,	/*!< in: rollback segment id */
	uint32_t page_no,	/*!< in: page number */
	uint16_t offset);	/*!< in: offset of the undo entry within page */
/***********************************************************************//**
Decodes a roll pointer. */
UNIV_INLINE
void
trx_undo_decode_roll_ptr(
/*=====================*/
	roll_ptr_t	roll_ptr,	/*!< in: roll pointer */
	bool*		is_insert,	/*!< out: TRUE if insert undo log */
	ulint*		rseg_id,	/*!< out: rollback segment id */
	uint32_t*	page_no,	/*!< out: page number */
	uint16_t*	offset);	/*!< out: offset of the undo
					entry within page */
/***********************************************************************//**
Determine if DB_ROLL_PTR is of the insert type.
@return true if insert */
UNIV_INLINE
bool
trx_undo_roll_ptr_is_insert(
/*========================*/
	roll_ptr_t	roll_ptr);	/*!< in: roll pointer */
/***********************************************************************//**
Returns true if the record is of the insert type.
@return true if the record was freshly inserted (not updated). */
UNIV_INLINE
bool
trx_undo_trx_id_is_insert(
/*======================*/
	const byte*	trx_id)	/*!< in: DB_TRX_ID, followed by DB_ROLL_PTR */
	MY_ATTRIBUTE((warn_unused_result));
/** Write DB_ROLL_PTR.
@param[out]	ptr		buffer
@param[in]	roll_ptr	DB_ROLL_PTR value */
inline void trx_write_roll_ptr(byte* ptr, roll_ptr_t roll_ptr)
{
	compile_time_assert(DATA_ROLL_PTR_LEN == 7);
	mach_write_to_7(ptr, roll_ptr);
}
/** Read DB_ROLL_PTR.
@param[in]	ptr	buffer
@return roll ptr */
inline roll_ptr_t trx_read_roll_ptr(const byte* ptr)
{
	compile_time_assert(DATA_ROLL_PTR_LEN == 7);
	return mach_read_from_7(ptr);
}

/** Get the next record in an undo log.
@param[in]      undo_page       undo log page
@param[in]      rec             undo record offset in the page
@param[in]      page_no         undo log header page number
@param[in]      offset          undo log header offset on page
@return undo log record, the page latched, NULL if none */
inline trx_undo_rec_t*
trx_undo_page_get_next_rec(const buf_block_t *undo_page, uint16_t rec,
                           uint32_t page_no, uint16_t offset);
/** Get the previous record in an undo log.
@param[in,out]  block   undo log page
@param[in]      rec     undo record offset in the page
@param[in]      page_no undo log header page number
@param[in]      offset  undo log header offset on page
@param[in]      shared  latching mode: true=RW_S_LATCH, false=RW_X_LATCH
@param[in,out]  mtr     mini-transaction
@return undo log record, the page latched, NULL if none */
trx_undo_rec_t*
trx_undo_get_prev_rec(buf_block_t *&block, uint16_t rec, uint32_t page_no,
                      uint16_t offset, bool shared, mtr_t *mtr);

/** Get the first undo log record on a page.
@param[in]	block	undo log page
@param[in]	page_no	undo log header page number
@param[in]	offset	undo log header page offset
@return	pointer to first record
@retval	nullptr	if none exists */
trx_undo_rec_t*
trx_undo_page_get_first_rec(const buf_block_t *block, uint32_t page_no,
                            uint16_t offset);

/** Initialize an undo log page.
NOTE: This corresponds to a redo log record and must not be changed!
@see mtr_t::undo_create()
@param[in,out]	block	undo log page */
void trx_undo_page_init(const buf_block_t &block);

/** Allocate an undo log page.
@param[in,out]	undo	undo log
@param[in,out]	mtr	mini-transaction that does not hold any page latch
@param[out]	err	error code
@return	X-latched block if success
@retval	nullptr	on failure */
buf_block_t *trx_undo_add_page(trx_undo_t *undo, mtr_t *mtr, dberr_t *err)
  MY_ATTRIBUTE((nonnull, warn_unused_result));

/** Free the last undo log page. The caller must hold the rseg mutex.
@param[in,out]	undo	undo log
@param[in,out]	mtr	mini-transaction that does not hold any undo log page
			or that has allocated the undo log page
@return error code */
dberr_t trx_undo_free_last_page(trx_undo_t *undo, mtr_t *mtr)
  MY_ATTRIBUTE((nonnull, warn_unused_result));

/** Try to truncate the undo logs.
@param trx transaction
@return error code */
dberr_t trx_undo_try_truncate(const trx_t &trx);

/** Truncate the head of an undo log.
NOTE that only whole pages are freed; the header page is not
freed, but emptied, if all the records there are below the limit.
@param[in,out]	rseg		rollback segment
@param[in]	hdr_page_no	header page number
@param[in]	hdr_offset	header offset on the page
@param[in]	limit		first undo number to preserve
(everything below the limit will be truncated)
@return error code */
dberr_t
trx_undo_truncate_start(
	trx_rseg_t*	rseg,
	uint32_t	hdr_page_no,
	uint16_t	hdr_offset,
	undo_no_t	limit)
	MY_ATTRIBUTE((nonnull, warn_unused_result));
/** Mark that an undo log header belongs to a data dictionary transaction.
@param[in]	trx	dictionary transaction
@param[in,out]	undo	undo log
@param[in,out]	mtr	mini-transaction */
void trx_undo_mark_as_dict(const trx_t* trx, trx_undo_t* undo, mtr_t* mtr);
/** Assign an undo log for a persistent transaction.
A new undo log is created or a cached undo log reused.
@param[in,out]	trx	transaction
@param[out]	err	error code
@param[in,out]	mtr	mini-transaction
@return	the undo log block
@retval	NULL	on error */
buf_block_t*
trx_undo_assign(trx_t* trx, dberr_t* err, mtr_t* mtr)
	MY_ATTRIBUTE((nonnull));
/** Assign an undo log for a transaction.
A new undo log is created or a cached undo log reused.
@tparam is_temp  whether this is temporary undo log
@param[in,out]	trx	transaction
@param[in]	rseg	rollback segment
@param[out]	undo	the undo log
@param[in,out]	mtr	mini-transaction
@param[out]	err	error code
@return	the undo log block
@retval	nullptr	on error */
template<bool is_temp>
buf_block_t*
trx_undo_assign_low(trx_t *trx, trx_rseg_t *rseg, trx_undo_t **undo,
                    mtr_t *mtr, dberr_t *err)
	MY_ATTRIBUTE((nonnull, warn_unused_result));

/** Set the state of the undo log segment at a XA PREPARE or XA ROLLBACK.
@param[in,out]	trx		transaction
@param[in,out]	undo		undo log
@param[in]	rollback	false=XA PREPARE, true=XA ROLLBACK
@param[in,out]	mtr		mini-transaction */
void trx_undo_set_state_at_prepare(trx_t *trx, trx_undo_t *undo, bool rollback,
                                   mtr_t *mtr)
  MY_ATTRIBUTE((nonnull));

/** At shutdown, frees the undo logs of a transaction. */
void
trx_undo_free_at_shutdown(trx_t *trx);

/** Read an undo log when starting up the database.
@param[in,out]	rseg		rollback segment
@param[in]	id		rollback segment slot
@param[in]	page_no		undo log segment page number
@return	the undo log
@retval nullptr on error */
trx_undo_t *
trx_undo_mem_create_at_db_start(trx_rseg_t *rseg, ulint id, uint32_t page_no);

#endif /* !UNIV_INNOCHECKSUM */

/** the only rollback segment type since MariaDB 10.3.1 */
constexpr uint16_t TRX_UNDO_UPDATE= 2;
/* TRX_UNDO_STATE values of an undo log segment */
/** contains an undo log of an active transaction */
constexpr uint16_t TRX_UNDO_ACTIVE = 1;
/** cached for quick reuse */
constexpr uint16_t TRX_UNDO_CACHED = 2;
/** can be freed in purge when all undo data in it is removed */
constexpr uint16_t TRX_UNDO_TO_PURGE = 4;
/** contains an undo log of a prepared transaction */
constexpr uint16_t TRX_UNDO_PREPARED = 5;

#ifndef UNIV_INNOCHECKSUM

/** Transaction undo log memory object; modified by the thread associated
with the transaction. */

struct trx_undo_t {
	/*-----------------------------*/
	ulint		id;		/*!< undo log slot number within the
					rollback segment */
	ulint		state;		/*!< state of the corresponding undo log
					segment */
	trx_id_t	trx_id;		/*!< id of the trx assigned to the undo
					log */
	XID		xid;		/*!< X/Open XA transaction
					identification */
	bool		dict_operation;	/*!< TRUE if a dict operation trx */
	trx_rseg_t*	rseg;		/*!< rseg where the undo log belongs */
	/*-----------------------------*/
	uint32_t	hdr_page_no;	/*!< page number of the header page in
					the undo log */
	uint32_t	last_page_no;	/*!< page number of the last page in the
					undo log; this may differ from
					top_page_no during a rollback */
	uint16_t	hdr_offset;	/*!< header offset of the undo log on
				       	the page */
	uint32_t	size;		/*!< current size in pages */
	/*-----------------------------*/
	uint32_t	top_page_no;	/*!< page number where the latest undo
					log record was catenated; during
					rollback the page from which the latest
					undo record was chosen */
	uint16_t	top_offset;	/*!< offset of the latest undo record,
					i.e., the topmost element in the undo
					log if we think of it as a stack */
	undo_no_t	top_undo_no;	/*!< undo number of the latest record
					(IB_ID_MAX if the undo log is empty) */
	buf_block_t*	guess_block;	/*!< guess for the buffer block where
					the top page might reside */

	/** @return whether the undo log is empty */
	bool empty() const { return top_undo_no == IB_ID_MAX; }

	/*-----------------------------*/
	UT_LIST_NODE_T(trx_undo_t) undo_list;
					/*!< undo log objects in the rollback
					segment are chained into lists */
};

/** Cache a pointer to an undo record in a latched buffer pool page,
parse the undo log record and store the record type, update vector
and compiler information */
class UndorecApplier
{
  /** Undo log block page id */
  page_id_t page_id;
  /** Pointer to within undo log record */
  const trx_undo_rec_t *undo_rec;
  /** Undo log record type */
  byte type;
  /** compiler information */
  byte cmpl_info;
  /** page_offset(undo_rec) of the start of undo_rec */
  uint16_t offset;
  /** Transaction id of the undo log */
  const trx_id_t trx_id;
  /** Update vector */
  upd_t *update;
  /** memory heap which can be used to build previous version of
  the index record and its offsets */
  mem_heap_t *heap;
  /** mini-transaction for accessing B-tree pages */
  mtr_t mtr;

public:
  UndorecApplier(page_id_t page_id, trx_id_t trx_id) :
    page_id(page_id), trx_id(trx_id), heap(mem_heap_create(100))
  {
  }

  /** Assign the next page id */
  void assign_next(const page_id_t next_page_id)
  {
    page_id= next_page_id;
  }

  page_id_t get_page_id() const { return page_id; }

  /** Handle the DML undo log and apply it on online indexes */
  inline void apply_undo_rec(const trx_undo_rec_t *rec);

  ~UndorecApplier()
  {
    mem_heap_free(heap);
  }

private:
  /** Handle the insert undo log and apply it on online indexes
  @param  tuple		row reference from undo log record
  @param  clust_index	clustered index */
  void log_insert(const dtuple_t &tuple, dict_index_t *clust_index);

  /** Handle the update, delete undo log and apply it on online
  indexes.
  @param  tuple		row reference from undo log record
  @param  clust_index	clustered index */
  void log_update(const dtuple_t &tuple, dict_index_t *clust_index);

  /** Check whether the given roll pointer is generated by
  the current undo log record information stored.
  @return true if roll pointer matches with current undo log info */
  inline bool is_same(roll_ptr_t roll_ptr) const;

  /** Clear the undo log record information */
  void clear_undo_rec()
  {
    undo_rec= nullptr;
    cmpl_info= 0;
    type= 0;
    update= nullptr;
    mem_heap_empty(heap);
  }

  /** Get the correct version of the clustered index record that
  was modified by the current undo log record. Because there could
  be the multiple successive updates of the same record within the
  same transaction.
  @param	tuple		tuple contains primary key value
  @param	index		clustered index
  @param[out]	clust_rec	current clustered index record
  @param	offsets		offsets points to the record
  @return clustered index record which was changed by
  the undo log record or nullptr when there is no clustered
  index record changed by undo log record */
  const rec_t* get_old_rec(const dtuple_t &tuple, dict_index_t *index,
                           const rec_t **clust_rec, rec_offs **offsets);
};

#endif /* !UNIV_INNOCHECKSUM */

/** The offset of the undo log page header on pages of the undo log */
#define	TRX_UNDO_PAGE_HDR	FSEG_PAGE_DATA
/*-------------------------------------------------------------*/
/** Transaction undo log page header offsets */
/* @{ */
#define	TRX_UNDO_PAGE_TYPE	0	/*!< unused; 0 (before MariaDB 10.3.1:
					1=TRX_UNDO_INSERT or
					2=TRX_UNDO_UPDATE) */
#define	TRX_UNDO_PAGE_START	2	/*!< Byte offset where the undo log
					records for the LATEST transaction
					start on this page (remember that
					in an update undo log, the first page
					can contain several undo logs) */
#define	TRX_UNDO_PAGE_FREE	4	/*!< On each page of the undo log this
					field contains the byte offset of the
					first free byte on the page */
#define TRX_UNDO_PAGE_NODE	6	/*!< The file list node in the chain
					of undo log pages */
/*-------------------------------------------------------------*/
#define TRX_UNDO_PAGE_HDR_SIZE	(6 + FLST_NODE_SIZE)
					/*!< Size of the transaction undo
					log page header, in bytes */
/* @} */

/** An update undo segment with just one page can be reused if it has
at most this many bytes used; we must leave space at least for one new undo
log header on the page */

#define TRX_UNDO_PAGE_REUSE_LIMIT	(3 << (srv_page_size_shift - 2))

/* An update undo log segment may contain several undo logs on its first page
if the undo logs took so little space that the segment could be cached and
reused. All the undo log headers are then on the first page, and the last one
owns the undo log records on subsequent pages if the segment is bigger than
one page. If an undo log is stored in a segment, then on the first page it is
allowed to have zero undo records, but if the segment extends to several
pages, then all the rest of the pages must contain at least one undo log
record. */

/** The offset of the undo log segment header on the first page of the undo
log segment */

#define	TRX_UNDO_SEG_HDR	(TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_HDR_SIZE)
/** Undo log segment header */
/* @{ */
/*-------------------------------------------------------------*/
#define	TRX_UNDO_STATE		0	/*!< TRX_UNDO_ACTIVE, ... */

#ifndef UNIV_INNOCHECKSUM

#define	TRX_UNDO_LAST_LOG	2	/*!< Offset of the last undo log header
					on the segment header page, 0 if
					none */
#define	TRX_UNDO_FSEG_HEADER	4	/*!< Header for the file segment which
					the undo log segment occupies */
#define	TRX_UNDO_PAGE_LIST	(4 + FSEG_HEADER_SIZE)
					/*!< Base node for the list of pages in
					the undo log segment; defined only on
					the undo log segment's first page */
/*-------------------------------------------------------------*/
/** Size of the undo log segment header */
#define TRX_UNDO_SEG_HDR_SIZE	(4 + FSEG_HEADER_SIZE + FLST_BASE_NODE_SIZE)
/* @} */

/** The undo log header. There can be several undo log headers on the first
page of an update undo log segment. */
/* @{ */
/*-------------------------------------------------------------*/
/** Transaction start identifier, or 0 if the undo log segment has been
completely purged and trx_purge_free_segment() has started freeing it */
#define	TRX_UNDO_TRX_ID		0
/** Transaction end identifier (if the log is in a history list),
or 0 if the transaction has not been committed */
#define	TRX_UNDO_TRX_NO		8
/* Before MariaDB 10.3.1, when purge did not reset DB_TRX_ID of
surviving user records, this used to be called TRX_UNDO_DEL_MARKS.

This field was removed in MariaDB 11.0.

The value 1 indicates that purge needs to process the undo log segment.
The value 0 indicates that all of it has been processed, and
trx_purge_free_segment() has been invoked, so the log is not safe to access.

Before MariaDB 10.3.1, a log segment may carry the value 0 even before
trx_purge_free_segment() was called, for those undo log records for
which purge would not result in removing delete-marked records. */
/*#define	TRX_UNDO_NEEDS_PURGE	16*/
#define	TRX_UNDO_LOG_START	18	/*!< Offset of the first undo log record
					of this log on the header page; purge
					may remove undo log record from the
					log start, and therefore this is not
					necessarily the same as this log
					header end offset */
#define	TRX_UNDO_XID_EXISTS	20	/*!< TRUE if undo log header includes
					X/Open XA transaction identification
					XID */
#define	TRX_UNDO_DICT_TRANS	21	/*!< TRUE if the transaction is a table
					create, index create, or drop
					transaction: in recovery
					the transaction cannot be rolled back
					in the usual way: a 'rollback' rather
					means dropping the created or dropped
					table, if it still exists */
#define TRX_UNDO_TABLE_ID	22	/*!< Id of the table if the preceding
					field is TRUE */
#define	TRX_UNDO_NEXT_LOG	30	/*!< Offset of the next undo log header
					on this page, 0 if none */
#define	TRX_UNDO_PREV_LOG	32	/*!< Offset of the previous undo log
					header on this page, 0 if none */
#define TRX_UNDO_HISTORY_NODE	34	/*!< If the log is put to the history
					list, the file list node is here */
/*-------------------------------------------------------------*/
/** Size of the undo log header without XID information */
#define TRX_UNDO_LOG_OLD_HDR_SIZE (34 + FLST_NODE_SIZE)

/** X/Open XA Transaction Identification (XID) */
/* @{ */
/** xid_t::formatID */
#define	TRX_UNDO_XA_FORMAT	(TRX_UNDO_LOG_OLD_HDR_SIZE)
/** xid_t::gtrid_length */
#define	TRX_UNDO_XA_TRID_LEN	(TRX_UNDO_XA_FORMAT + 4)
/** xid_t::bqual_length */
#define	TRX_UNDO_XA_BQUAL_LEN	(TRX_UNDO_XA_TRID_LEN + 4)
/** Distributed transaction identifier data */
#define	TRX_UNDO_XA_XID		(TRX_UNDO_XA_BQUAL_LEN + 4)
/*--------------------------------------------------------------*/
#define TRX_UNDO_LOG_XA_HDR_SIZE (TRX_UNDO_XA_XID + XIDDATASIZE)
					/*!< Total size of the undo log header
					with the XA XID */
/* @} */

#include "trx0undo.inl"
#endif /* !UNIV_INNOCHECKSUM */

#endif