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
 
#include "fut0lst.h"
#include "mtr0mtr.h"
#include "page0types.h"
#include "sql/xa.h"
#include "trx0sys.h"
#include "trx0types.h"
#include "trx0xa.h"
#include "univ.i"
 
#ifndef UNIV_HOTBACKUP
/** Returns true if the roll pointer is of the insert type.
 @return true if insert undo log */
static 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). */
[[nodiscard]] static inline bool trx_undo_trx_id_is_insert(
    const byte *trx_id); /*!< in: DB_TRX_ID, followed by DB_ROLL_PTR */
#endif                   /* !UNIV_HOTBACKUP */
 
/** Writes a roll ptr to an index page. In case that the size changes in
some future version, this function should be used instead of
mach_write_...
@param[in]      ptr             pointer to memory where written
@param[in]      roll_ptr        roll ptr */
static inline void trx_write_roll_ptr(byte *ptr, roll_ptr_t roll_ptr);
 
/** Reads a roll ptr from an index page. In case that the roll ptr size
 changes in some future version, this function should be used instead of
 mach_read_...
 @return roll ptr */
static inline roll_ptr_t trx_read_roll_ptr(
    const byte *ptr); /*!< in: pointer to memory from where to read */
#ifndef UNIV_HOTBACKUP
 
/** Gets an undo log page and x-latches it.
@param[in]      page_id         Page id
@param[in]      page_size       Page size
@param[in,out]  mtr             Mini-transaction
@return pointer to page x-latched */
static inline page_t *trx_undo_page_get(const page_id_t &page_id,
                                        const page_size_t &page_size,
                                        mtr_t *mtr);
 
/** Gets an undo log page and s-latches it.
@param[in]      page_id         Page id
@param[in]      page_size       Page size
@param[in,out]  mtr             Mini-transaction
@return pointer to page s-latched */
static inline page_t *trx_undo_page_get_s_latched(const page_id_t &page_id,
                                                  const page_size_t &page_size,
                                                  mtr_t *mtr);
 
/** Returns the previous undo record on the page in the specified log, or
NULL if none exists.
@param[in]      rec             undo log record
@param[in]      page_no         undo log header page number
@param[in]      offset          undo log header offset on page
@return pointer to record, NULL if none */
static inline trx_undo_rec_t *trx_undo_page_get_prev_rec(trx_undo_rec_t *rec,
                                                         page_no_t page_no,
                                                         ulint offset);
 
/** Returns the next undo log record on the page in the specified log, or
NULL if none exists.
@param[in]      rec             undo log record
@param[in]      page_no         undo log header page number
@param[in]      offset          undo log header offset on page
@return pointer to record, NULL if none */
static inline trx_undo_rec_t *trx_undo_page_get_next_rec(trx_undo_rec_t *rec,
                                                         page_no_t page_no,
                                                         ulint offset);
 
/** Returns the last undo record on the page in the specified undo log, or
NULL if none exists.
@param[in]      undo_page       undo log page
@param[in]      page_no         undo log header page number
@param[in]      offset          undo log header offset on page
@return pointer to record, NULL if none */
static inline trx_undo_rec_t *trx_undo_page_get_last_rec(page_t *undo_page,
                                                         page_no_t page_no,
                                                         ulint offset);
 
/** Returns the first undo record on the page in the specified undo log, or
NULL if none exists.
@param[in]      undo_page       undo log page
@param[in]      page_no         undo log header page number
@param[in]      offset          undo log header offset on page
@return pointer to record, NULL if none */
static inline trx_undo_rec_t *trx_undo_page_get_first_rec(page_t *undo_page,
                                                          page_no_t page_no,
                                                          ulint offset);
 
/** Gets the previous record in an undo log.
NOTE! In case of shared=false, which is used in scanning for tablespace ids, but
not in rollback, this function might skip over non-relevant records.
@param[in]     rec             undo record
@param[in]     page_no         undo log header page number
@param[in]     offset          undo log header offset on page
@param[in]     shared          true=S-latch, false=X-latch
@param[in,out] mtr             mtr
@return undo log record, the page s-latched, NULL if none */
trx_undo_rec_t *trx_undo_get_prev_rec(trx_undo_rec_t *rec, page_no_t page_no,
                                      ulint offset, bool shared, mtr_t *mtr);
 
/** Gets the next record in an undo log.
 @return undo log record, the page s-latched, NULL if none */
trx_undo_rec_t *trx_undo_get_next_rec(
    trx_undo_rec_t *rec, /*!< in: undo record */
    page_no_t page_no,   /*!< in: undo log header page number */
    ulint offset,        /*!< in: undo log header offset on page */
    mtr_t *mtr);         /*!< in: mtr */
 
/** Gets the first record in an undo log.
@param[out]     modifier_trx_id The modifier trx identifier.
@param[in]      space           Undo log header space
@param[in]      page_size       Page size
@param[in]      page_no         Undo log header page number
@param[in]      offset          Undo log header offset on page
@param[in]      mode            Latching mode: RW_S_LATCH or 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_first_rec(trx_id_t *modifier_trx_id,
                                       space_id_t space,
                                       const page_size_t &page_size,
                                       page_no_t page_no, ulint offset,
                                       ulint mode, mtr_t *mtr);
 
/** Tries to add a page to the undo log segment where the undo log is placed.
 @return X-latched block if success, else NULL */
[[nodiscard]] buf_block_t *trx_undo_add_page(
    trx_t *trx,               /*!< in: transaction */
    trx_undo_t *undo,         /*!< in: undo log memory object */
    trx_undo_ptr_t *undo_ptr, /*!< in: assign undo log from
                              referred rollback segment. */
    mtr_t *mtr);              /*!< in: mtr which does not have
                             a latch to any undo log page;
                             the caller must have reserved
                             the rollback segment mutex */
 
/** Frees the last undo log page.
 The caller must hold the rollback segment mutex.
 @param[in] trx transaction
 @param[in,out] undo  undo log memory copy
 @param[in,out] mtr mini-transaction which does not have a latch to any undo log
 page or which has allocated the undo log page */
void trx_undo_free_last_page_func(IF_DEBUG(const trx_t *trx, ) trx_undo_t *undo,
                                  mtr_t *mtr);
 
static inline void trx_undo_free_last_page(const trx_t *trx [[maybe_unused]],
                                           trx_undo_t *undo, mtr_t *mtr) {
  trx_undo_free_last_page_func(IF_DEBUG(trx, ) undo, mtr);
}
 
/** Truncates an undo log from the end. This function is used during
a rollback to free space from an undo log.
@param[in]  trx    transaction for this undo log
@param[in]  undo   undo log
@param[in]  limit  all undo records with undo number;
                   This value should be truncated. */
void trx_undo_truncate_end_func(IF_DEBUG(const trx_t *trx, ) trx_undo_t *undo,
                                undo_no_t limit);
 
static inline void trx_undo_truncate_end(const trx_t *trx [[maybe_unused]],
                                         trx_undo_t *undo, undo_no_t limit) {
  trx_undo_truncate_end_func(IF_DEBUG(trx, ) undo, limit);
}
 
/** 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) */
void trx_undo_truncate_start(trx_rseg_t *rseg, page_no_t hdr_page_no,
                             ulint hdr_offset, undo_no_t limit);
 
/** Initializes the undo log lists for a rollback segment memory copy.
 This function is only called when the database is started or a new
 rollback segment created.
 @return the combined size of undo log segments in pages */
ulint trx_undo_lists_init(
    trx_rseg_t *rseg); /*!< in: rollback segment memory object */
 
/** Assigns an undo log for a transaction. A new undo log is created or a cached
 undo log reused.
 @return DB_SUCCESS if undo log assign successful, possible error codes
 are: DB_TOO_MANY_CONCURRENT_TRXS DB_OUT_OF_FILE_SPACE DB_READ_ONLY
 DB_OUT_OF_MEMORY */
[[nodiscard]] dberr_t trx_undo_assign_undo(
    trx_t *trx,               /*!< in: transaction */
    trx_undo_ptr_t *undo_ptr, /*!< in: assign undo log from
                              referred rollback segment. */
    ulint type);              /*!< in: TRX_UNDO_INSERT or
                             TRX_UNDO_UPDATE */
 
/** Sets the state of the undo log segment at a transaction finish.
 @param[in] undo    undo log memory copy
 @param[in] mtr     Mini-transaction
 @return undo log segment header page, x-latched
 */
page_t *trx_undo_set_state_at_finish(trx_undo_t *undo, mtr_t *mtr);
 
/** Set the state of the undo log segment at a XA PREPARE or XA ROLLBACK.
@param[in,out]  trx             Transaction
@param[in,out]  undo            Insert_undo or update_undo log
@param[in]      rollback        false=XA PREPARE, true=XA ROLLBACK
@param[in,out]  mtr             Mini-transaction
@return undo log segment header page, x-latched */
page_t *trx_undo_set_state_at_prepare(trx_t *trx, trx_undo_t *undo,
                                      bool rollback, mtr_t *mtr);
 
/** Set the state of the undo log segment as prepared in TC.
@param[in,out] trx   Transaction
@param[in,out] undo  Insert_undo or update_undo log
@param[in,out] mtr   Mini-transaction
@return undo log segment header page, x-latched */
page_t *trx_undo_set_prepared_in_tc(trx_t *trx, trx_undo_t *undo, mtr_t *mtr);
 
/** Adds the update undo log header as the first in the history list, and
 frees the memory object, or puts it to the list of cached update undo log
 segments.
@param[in] trx Trx owning the update undo log
@param[in] undo_ptr Update undo log.
@param[in] undo_page Update undo log header page, x-latched
@param[in] update_rseg_history_len If true: update rseg history len else
skip updating it.
@param[in] n_added_logs Number of logs added
@param[in] mtr Mini-transaction */
void trx_undo_update_cleanup(trx_t *trx, trx_undo_ptr_t *undo_ptr,
                             page_t *undo_page, bool update_rseg_history_len,
 
                             ulint n_added_logs, mtr_t *mtr);
 
/** Frees an insert undo log after a transaction commit or rollback.
Knowledge of inserts is not needed after a commit or rollback, therefore
the data can be discarded.
@param[in,out]  undo_ptr        undo log to clean up
@param[in]      noredo          whether the undo tablespace is redo logged */
void trx_undo_insert_cleanup(trx_undo_ptr_t *undo_ptr, bool noredo);
 
/** Frees the trx_undo_t objects for logs of a transaction which was either
PREPARED or (ACTIVE and recovered).
@param[in]     trx       transaction which undo logs are freed
@param[in]     prepared  whether or not the undo segment is in prepared or
                         prepared in tc states */
void trx_undo_free_trx_with_prepared_or_active_logs(trx_t *trx,
                                                    bool prepared) UNIV_COLD;
 
/* Forward declaration. */
namespace undo {
struct Tablespace;
class Truncate;
}  // namespace undo
 
/** Truncate UNDO tablespace, reinitialize header and rseg.
@param[in]  marked_space  UNDO tablespace to truncate
@return true if success else false. */
bool trx_undo_truncate_tablespace(undo_truncate::Tablespace *marked_space);
 
#endif /* !UNIV_HOTBACKUP */
 
/** Parses the redo log entry of an undo log page initialization.
 @return end of log record or NULL */
byte *trx_undo_parse_page_init(const byte *ptr,     /*!< in: buffer */
                               const byte *end_ptr, /*!< in: buffer end */
                               page_t *page,        /*!< in: page or NULL */
                               mtr_t *mtr);         /*!< in: mtr or NULL */
 
/** Parse the redo log entry of an undo log page header create or reuse.
@param[in]      type    MLOG_UNDO_HDR_CREATE or MLOG_UNDO_HDR_REUSE
@param[in]      ptr     Redo log record
@param[in]      end_ptr End of log buffer
@param[in,out]  page    Page frame or NULL
@param[in,out]  mtr     Mini-transaction or NULL
@return end of log record or NULL */
byte *trx_undo_parse_page_header(mlog_id_t type, const byte *ptr,
                                 const byte *end_ptr, page_t *page, mtr_t *mtr);
 
/************************************************************************
Frees an undo log memory copy. */
void trx_undo_mem_free(trx_undo_t *undo); /* in: the undo object to be freed */
 
/** Types of an undo log segment */
/** contains undo entries for inserts */
constexpr uint32_t TRX_UNDO_INSERT = 1;
/** contains undo entries for updates and delete markings: in short, modifys
 (the name 'UPDATE' is a historical relic) */
constexpr uint32_t TRX_UNDO_UPDATE = 2;
 
/* States of an undo log segment */
/** contains an undo log of an active  transaction */
constexpr uint32_t TRX_UNDO_ACTIVE = 1;
/** cached for quick reuse */
constexpr uint32_t TRX_UNDO_CACHED = 2;
/** insert undo segment can be freed */
constexpr uint32_t TRX_UNDO_TO_FREE = 3;
/** update undo segment will not be reused: it can be freed in purge when all
 undo data in it is removed */
constexpr uint32_t TRX_UNDO_TO_PURGE = 4;
/** contains an undo log of an prepared transaction for a server version older
than 8.0.29 */
constexpr uint32_t TRX_UNDO_PREPARED_80028 = 5;
/** contains an undo log of an prepared transaction */
constexpr uint32_t TRX_UNDO_PREPARED = 6;
/* contains an undo log of a prepared transaction that has been processed by the
transaction coordinator */
constexpr uint32_t TRX_UNDO_PREPARED_IN_TC = 7;
 
#ifndef UNIV_HOTBACKUP
/** Transaction undo log memory object; this is protected by the undo_mutex
in the corresponding transaction object */
 
struct trx_undo_t {
  /** Undo log may could be allocated to store transaction GTIDs. */
  enum class Gtid_storage {
    /* No storage is allocated for GTID. */
    NONE,
    /* Storage is allocated for commit GTID. */
    COMMIT,
    /* Storage is allocated for both prepare and commit GTID. For external
    XA transaction, we have GTID fr both prepare and commit. */
    PREPARE_AND_COMMIT
  };
 
  /** Check if space for GTID is allocated in undo.
  @param[in]    is_prepare      if XA prepare GTID
  @return true iff space for GTID is allocated. */
  bool gtid_allocated(bool is_prepare) const;
 
  /** Get offset and flag for GTID stored in undo.
  @param[in]    is_prepare      if XA prepare GTID
  @return GTID flag and offset in a tuple. */
  std::tuple<int, size_t> gtid_get_details(bool is_prepare) const;
 
  /* Set undo segment to prepared state and set XID
  @param[in]     in_xid transaction XID. */
  inline void set_prepared(const XID *in_xid);
 
  /* Set undo segment to prepared in TC state and set XID */
  inline void set_prepared_in_tc();
 
  /* Checks whether or not this undo log segment is in prepared state, meaning,
  the `state` member variable is either `TRX_UNDO_PREPARED_80028`.
  `TRX_UNDO_PREPARED` or `TRX_UNDO_PREPARED_IN_TC`.
  @return true is the undo log segment is in prepared state, false otherwise.*/
  inline bool is_prepared() const;
 
  /*-----------------------------*/
  ulint id;        /*!< undo log slot number within the
                   rollback segment */
  ulint type;      /*!< TRX_UNDO_INSERT or
                   TRX_UNDO_UPDATE */
  ulint state;     /*!< state of the corresponding undo log
                   segment */
  bool del_marks;  /*!< relevant only in an update undo
                    log: this is true if the transaction may
                    have delete marked records, because of
                    a delete of a row or an update of an
                    indexed field; purge is then
                    necessary; also true if the transaction
                    has updated an externally stored
                    field */
  trx_id_t trx_id; /*!< id of the trx assigned to the undo
                   log */
  XID xid;         /*!< X/Open XA transaction
                   identification */
  ulint flag;      /*!< flag for current transaction XID and GTID.
                   Persisted in TRX_UNDO_FLAGS flag of undo header. */
 
  /** Storage space allocated for GTIDs. */
  Gtid_storage m_gtid_storage{Gtid_storage::NONE};
 
  bool dict_operation; /*!< true if a dict operation trx */
  trx_rseg_t *rseg;    /*!< rseg where the undo log belongs */
  /*-----------------------------*/
  space_id_t space; /*!< space id where the undo log
                    placed */
  page_size_t page_size;
  page_no_t hdr_page_no;  /*!< page number of the header page in
                          the undo log */
  ulint hdr_offset;       /*!< header offset of the undo log on
                          the page */
  page_no_t last_page_no; /*!< page number of the last page in the
                          undo log; this may differ from
                          top_page_no during a rollback */
  ulint size;             /*!< current size in pages */
  /*-----------------------------*/
  ulint empty;              /*!< true if the stack of undo log
                            records is currently empty */
  page_no_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 */
  ulint 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 */
  buf_block_t *guess_block; /*!< guess for the buffer block where
                            the top page might reside */
  /*-----------------------------*/
  UT_LIST_NODE_T(trx_undo_t) undo_list;
  /*!< undo log objects in the rollback
  segment are chained into lists */
};
 
UT_LIST_NODE_GETTER_DEFINITION(trx_undo_t, undo_list)
 
/** For saving GTID add update undo slot, if required.
@param[in]      trx             transaction
@param[in]      prepare         operation is prepare
@param[in]      rollback        operation is rollback
@return innodb error code. */
dberr_t trx_undo_gtid_add_update_undo(trx_t *trx, bool prepare, bool rollback);
 
/** Set GTID flag in undo if transaction has GTID/
@param[in,out]  trx             transaction
@param[in,out]  undo            undo log memory object
@param[in]      is_xa_prepare   GTID is for XA prepared transaction. */
void trx_undo_gtid_set(trx_t *trx, trx_undo_t *undo, bool is_xa_prepare);
 
/** Read and persist GTID from undo header during recovery.
@param[in]      undo_log        undo log header */
void trx_undo_gtid_read_and_persist(trx_ulogf_t *undo_log);
 
/** Write GTID information to undo log header.
@param[in,out]  trx             transaction
@param[in,out]  undo_header     undo log header
@param[in,out]  undo            undo log memory object
@param[in,out]  mtr             minit transaction for write
@param[in]      is_xa_prepare   GTID is for XA prepared transaction. */
void trx_undo_gtid_write(trx_t *trx, trx_ulogf_t *undo_header, trx_undo_t *undo,
                         mtr_t *mtr, bool is_xa_prepare);
 
#endif /* !UNIV_HOTBACKUP */
 
/** The offset of the undo log page header on pages of the undo log */
constexpr uint32_t TRX_UNDO_PAGE_HDR = FSEG_PAGE_DATA;
/*-------------------------------------------------------------*/
/** Transaction undo log page header offsets */
/** @{ */
/** TRX_UNDO_INSERT or TRX_UNDO_UPDATE */
constexpr uint32_t TRX_UNDO_PAGE_TYPE = 0;
/** 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) */
constexpr uint32_t TRX_UNDO_PAGE_START = 2;
/** On each page of the undo log this field contains the byte offset of the
 first free byte on the page */
constexpr uint32_t TRX_UNDO_PAGE_FREE = 4;
/** The file list node in the chain of undo log pages */
constexpr uint32_t TRX_UNDO_PAGE_NODE = 6;
/*-------------------------------------------------------------*/
/** Size of the transaction undo log page header, in bytes */
constexpr uint32_t TRX_UNDO_PAGE_HDR_SIZE = 6 + FLST_NODE_SIZE;
 
/** @} */
 
/** 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 * UNIV_PAGE_SIZE / 4)
 
/* 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 */
 
constexpr uint32_t TRX_UNDO_SEG_HDR =
    TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_HDR_SIZE;
/** Undo log segment header */
/** @{ */
/*-------------------------------------------------------------*/
/** TRX_UNDO_ACTIVE, ... */
constexpr uint32_t TRX_UNDO_STATE = 0;
/** Offset of the last undo log header on the segment header page, 0 if none */
constexpr uint32_t TRX_UNDO_LAST_LOG = 2;
/** Header for the file segment which the undo log segment occupies */
constexpr uint32_t TRX_UNDO_FSEG_HEADER = 4;
/** Base node for the list of pages in the undo log segment; defined only on the
 undo log segment's first page */
constexpr uint32_t TRX_UNDO_PAGE_LIST = 4 + FSEG_HEADER_SIZE;
/*-------------------------------------------------------------*/
/** Size of the undo log segment header */
constexpr uint32_t 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 id */
constexpr uint32_t TRX_UNDO_TRX_ID = 0;
/** Transaction number of the transaction; defined only if the log is in a
 history list */
constexpr uint32_t TRX_UNDO_TRX_NO = 8;
/** Defined only in an update undo log: true if the transaction may have done
 delete markings of records, and thus purge is necessary */
constexpr uint32_t TRX_UNDO_DEL_MARKS = 16;
/** 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 */
constexpr uint32_t TRX_UNDO_LOG_START = 18;
/** Transaction UNDO flags in one byte. This is backward compatible as earlier
 we were storing either 1 or 0 for TRX_UNDO_XID_EXISTS. */
constexpr uint32_t TRX_UNDO_FLAGS = 20;
/** true if undo log header includes X/Open XA transaction identification XID */
constexpr uint32_t TRX_UNDO_FLAG_XID = 0x01;
/** true if undo log header includes GTID information from replication */
constexpr uint32_t TRX_UNDO_FLAG_GTID = 0x02;
/** true if undo log header includes GTID information for XA PREPARE */
constexpr uint32_t TRX_UNDO_FLAG_XA_PREPARE_GTID = 0x04;
/** 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 */
constexpr uint32_t TRX_UNDO_DICT_TRANS = 21;
/** Id of the table if the preceding field is true. Note: deprecated */
constexpr uint32_t TRX_UNDO_TABLE_ID = 22;
/** Offset of the next undo log header on this page, 0 if none */
constexpr uint32_t TRX_UNDO_NEXT_LOG = 30;
/** Offset of the previous undo log header on this page, 0 if none */
constexpr uint32_t TRX_UNDO_PREV_LOG = 32;
/** If the log is put to the history list, the file list node is here */
constexpr uint32_t TRX_UNDO_HISTORY_NODE = 34;
/*-------------------------------------------------------------*/
/** Size of the undo log header without XID information */
constexpr uint32_t TRX_UNDO_LOG_OLD_HDR_SIZE = 34 + FLST_NODE_SIZE;
 
/* Note: the writing of the undo log old header is coded by a log record
MLOG_UNDO_HDR_CREATE or MLOG_UNDO_HDR_REUSE. The appending of an XID to the
header is logged separately. In this sense, the XID is not really a member
of the undo log header. TODO: do not append the XID to the log header if XA
is not needed by the user. The XID wastes about 150 bytes of space in every
undo log. In the history list we may have millions of undo logs, which means
quite a large overhead. */
/** @} */
 
/** X/Open XA Transaction Identification (XID) */
/** @{ */
/** xid_t::formatID */
constexpr uint32_t TRX_UNDO_XA_FORMAT = TRX_UNDO_LOG_OLD_HDR_SIZE;
/** xid_t::gtrid_length */
constexpr uint32_t TRX_UNDO_XA_TRID_LEN = TRX_UNDO_XA_FORMAT + 4;
/** xid_t::bqual_length */
constexpr uint32_t TRX_UNDO_XA_BQUAL_LEN = TRX_UNDO_XA_TRID_LEN + 4;
/** Distributed transaction identifier data */
constexpr uint32_t TRX_UNDO_XA_XID = TRX_UNDO_XA_BQUAL_LEN + 4;
/*--------------------------------------------------------------*/
constexpr uint32_t TRX_UNDO_LOG_XA_HDR_SIZE = TRX_UNDO_XA_XID + XIDDATASIZE;
/*!< Total size of the undo log header
with the XA XID */
/** @} */
 
/* GTID is generated by replication when binlog and GTID mode is on. We
persist GTID with undo record till it is written to gtid_exeuted table.
GTID information is present when TRX_UNDO_FLAG_GTID set. It follows XID
information */
 
/** GTID version offset */
constexpr uint32_t TRX_UNDO_LOG_GTID_VERSION = TRX_UNDO_LOG_XA_HDR_SIZE;
 
/** GTID offset */
constexpr uint32_t TRX_UNDO_LOG_GTID = TRX_UNDO_LOG_XA_HDR_SIZE + 1;
 
/** Total length of GTID */
constexpr uint32_t TRX_UNDO_LOG_GTID_LEN = 64;
 
/** Total size with GTID information. */
constexpr uint32_t TRX_UNDO_LOG_GTID_HDR_SIZE =
    TRX_UNDO_LOG_GTID + TRX_UNDO_LOG_GTID_LEN;
 
/** GTID offset for XA Prepare. */
constexpr uint32_t TRX_UNDO_LOG_GTID_XA = TRX_UNDO_LOG_GTID_HDR_SIZE;
 
/** Total size with XA GTID information. For external XA transaction we need
to store both prepare and commit GTID. */
constexpr uint32_t TRX_UNDO_LOG_GTID_XA_HDR_SIZE =
    TRX_UNDO_LOG_GTID_HDR_SIZE + TRX_UNDO_LOG_GTID_LEN;
 
#include "trx0undo.ic"
#endif