mariadb/storage/innobase/include/trx0sys.h

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

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

/**************************************************//**
@file include/trx0sys.h
Transaction system

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

#ifndef trx0sys_h
#define trx0sys_h

#include "univ.i"

#include "trx0types.h"
#include "fsp0types.h"
#include "fil0fil.h"
#include "buf0buf.h"
#ifndef UNIV_HOTBACKUP
#include "mtr0mtr.h"
#include "ut0byte.h"
#include "mem0mem.h"
#include "sync0sync.h"
#include "ut0lst.h"
#include "ut0bh.h"
#include "read0types.h"
#include "page0types.h"
#include "ut0bh.h"
#ifdef WITH_WSREP
#include "trx0xa.h"
#endif /* WITH_WSREP */

typedef UT_LIST_BASE_NODE_T(trx_t) trx_list_t;

/** In a MySQL replication slave, in crash recovery we store the master log
file name and position here. */
/* @{ */
/** Master binlog file name */
extern char		trx_sys_mysql_master_log_name[];
/** Master binlog file position.  We have successfully got the updates
up to this position.  -1 means that no crash recovery was needed, or
there was no master log position info inside InnoDB.*/
extern ib_int64_t	trx_sys_mysql_master_log_pos;
/* @} */

/** If this MySQL server uses binary logging, after InnoDB has been inited
and if it has done a crash recovery, we store the binlog file name and position
here. */
/* @{ */
/** Binlog file name */
extern char		trx_sys_mysql_bin_log_name[];
/** Binlog file position, or -1 if unknown */
extern ib_int64_t	trx_sys_mysql_bin_log_pos;
/* @} */

/** The transaction system */
extern trx_sys_t*	trx_sys;

/***************************************************************//**
Checks if a page address is the trx sys header page.
@return	TRUE if trx sys header page */
UNIV_INLINE
ibool
trx_sys_hdr_page(
/*=============*/
	ulint	space,	/*!< in: space */
	ulint	page_no);/*!< in: page number */
/*****************************************************************//**
Creates and initializes the central memory structures for the transaction
system. This is called when the database is started.
@return min binary heap of rsegs to purge */
UNIV_INTERN
ib_bh_t*
trx_sys_init_at_db_start(void);
/*==========================*/
/*****************************************************************//**
Creates the trx_sys instance and initializes ib_bh and mutex. */
UNIV_INTERN
void
trx_sys_create(void);
/*================*/
/*****************************************************************//**
Creates and initializes the transaction system at the database creation. */
UNIV_INTERN
void
trx_sys_create_sys_pages(void);
/*==========================*/
/****************************************************************//**
Looks for a free slot for a rollback segment in the trx system file copy.
@return	slot index or ULINT_UNDEFINED if not found */
UNIV_INTERN
ulint
trx_sysf_rseg_find_free(
/*====================*/
	mtr_t*		mtr);		/*!< in: mtr */
/***************************************************************//**
Gets the pointer in the nth slot of the rseg array.
@return	pointer to rseg object, NULL if slot not in use */
UNIV_INLINE
trx_rseg_t*
trx_sys_get_nth_rseg(
/*=================*/
	trx_sys_t*	sys,	/*!< in: trx system */
	ulint		n);	/*!< in: index of slot */
/**********************************************************************//**
Gets a pointer to the transaction system file copy and x-locks its page.
@return	pointer to system file copy, page x-locked */
UNIV_INLINE
trx_sysf_t*
trx_sysf_get(
/*=========*/
	mtr_t*	mtr);	/*!< in: mtr */
/*****************************************************************//**
Gets the space of the nth rollback segment slot in the trx system
file copy.
@return	space id */
UNIV_INLINE
ulint
trx_sysf_rseg_get_space(
/*====================*/
	trx_sysf_t*	sys_header,	/*!< in: trx sys file copy */
	ulint		i,		/*!< in: slot index == rseg id */
	mtr_t*		mtr);		/*!< in: mtr */
/*****************************************************************//**
Gets the page number of the nth rollback segment slot in the trx system
file copy.
@return	page number, FIL_NULL if slot unused */
UNIV_INLINE
ulint
trx_sysf_rseg_get_page_no(
/*======================*/
	trx_sysf_t*	sys_header,	/*!< in: trx sys file copy */
	ulint		i,		/*!< in: slot index == rseg id */
	mtr_t*		mtr);		/*!< in: mtr */
/*****************************************************************//**
Sets the space id of the nth rollback segment slot in the trx system
file copy. */
UNIV_INLINE
void
trx_sysf_rseg_set_space(
/*====================*/
	trx_sysf_t*	sys_header,	/*!< in: trx sys file copy */
	ulint		i,		/*!< in: slot index == rseg id */
	ulint		space,		/*!< in: space id */
	mtr_t*		mtr);		/*!< in: mtr */
/*****************************************************************//**
Sets the page number of the nth rollback segment slot in the trx system
file copy. */
UNIV_INLINE
void
trx_sysf_rseg_set_page_no(
/*======================*/
	trx_sysf_t*	sys_header,	/*!< in: trx sys file copy */
	ulint		i,		/*!< in: slot index == rseg id */
	ulint		page_no,	/*!< in: page number, FIL_NULL if
					the slot is reset to unused */
	mtr_t*		mtr);		/*!< in: mtr */
/*****************************************************************//**
Allocates a new transaction id.
@return	new, allocated trx id */
UNIV_INLINE
trx_id_t
trx_sys_get_new_trx_id(void);
/*========================*/
/*****************************************************************//**
Determines the maximum transaction id.
@return maximum currently allocated trx id; will be stale after the
next call to trx_sys_get_new_trx_id() */
UNIV_INLINE
trx_id_t
trx_sys_get_max_trx_id(void);
/*========================*/

#ifdef UNIV_DEBUG
/* Flag to control TRX_RSEG_N_SLOTS behavior debugging. */
extern uint			trx_rseg_n_slots_debug;
#endif

/*****************************************************************//**
Writes a trx id to an index page. In case that the id size changes in
some future version, this function should be used instead of
mach_write_... */
UNIV_INLINE
void
trx_write_trx_id(
/*=============*/
	byte*		ptr,	/*!< in: pointer to memory where written */
	trx_id_t	id);	/*!< in: id */
/*****************************************************************//**
Reads a trx id from an index page. In case that the id size changes in
some future version, this function should be used instead of
mach_read_...
@return	id */
UNIV_INLINE
trx_id_t
trx_read_trx_id(
/*============*/
	const byte*	ptr);	/*!< in: pointer to memory from where to read */
/****************************************************************//**
Looks for the trx instance with the given id in the rw trx_list.
The caller must be holding trx_sys->mutex.
@return	the trx handle or NULL if not found;
the pointer must not be dereferenced unless lock_sys->mutex was
acquired before calling this function and is still being held */
UNIV_INLINE
trx_t*
trx_get_rw_trx_by_id(
/*=================*/
	trx_id_t	trx_id);/*!< in: trx id to search for */
/****************************************************************//**
Returns the minimum trx id in rw trx list. This is the smallest id for which
the trx can possibly be active. (But, you must look at the trx->state to
find out if the minimum trx id transaction itself is active, or already
committed.)
@return	the minimum trx id, or trx_sys->max_trx_id if the trx list is empty */
UNIV_INLINE
trx_id_t
trx_rw_min_trx_id(void);
/*===================*/
/****************************************************************//**
Checks if a rw transaction with the given id is active. Caller must hold
trx_sys->mutex in shared mode. If the caller is not holding
lock_sys->mutex, the transaction may already have been committed.
@return	transaction instance if active, or NULL;
the pointer must not be dereferenced unless lock_sys->mutex was
acquired before calling this function and is still being held */
UNIV_INLINE
trx_t*
trx_rw_is_active_low(
/*=================*/
	trx_id_t	trx_id,		/*!< in: trx id of the transaction */
	ibool*		corrupt);	/*!< in: NULL or pointer to a flag
					that will be set if corrupt */
/****************************************************************//**
Checks if a rw transaction with the given id is active. If the caller is
not holding lock_sys->mutex, the transaction may already have been
committed.
@return	transaction instance if active, or NULL;
the pointer must not be dereferenced unless lock_sys->mutex was
acquired before calling this function and is still being held */
UNIV_INLINE
trx_t*
trx_rw_is_active(
/*=============*/
	trx_id_t	trx_id,		/*!< in: trx id of the transaction */
	ibool*		corrupt);	/*!< in: NULL or pointer to a flag
					that will be set if corrupt */
#ifdef UNIV_DEBUG
/****************************************************************//**
Checks whether a trx is in one of rw_trx_list or ro_trx_list.
@return	TRUE if is in */
UNIV_INTERN
ibool
trx_in_trx_list(
/*============*/
	const trx_t*	in_trx)		/*!< in: transaction */
	MY_ATTRIBUTE((nonnull, warn_unused_result));
#endif /* UNIV_DEBUG */
#if defined UNIV_DEBUG || defined UNIV_BLOB_LIGHT_DEBUG
/***********************************************************//**
Assert that a transaction has been recovered.
@return TRUE */
UNIV_INLINE
ibool
trx_assert_recovered(
/*=================*/
	trx_id_t	trx_id)		/*!< in: transaction identifier */
	MY_ATTRIBUTE((warn_unused_result));
#endif /* UNIV_DEBUG || UNIV_BLOB_LIGHT_DEBUG */
/*****************************************************************//**
Updates the offset information about the end of the MySQL binlog entry
which corresponds to the transaction just being committed. In a MySQL
replication slave updates the latest master binlog position up to which
replication has proceeded. */
UNIV_INTERN
void
trx_sys_update_mysql_binlog_offset(
/*===============================*/
	const char*	file_name,/*!< in: MySQL log file name */
	ib_int64_t	offset,	/*!< in: position in that log file */
	ulint		field,	/*!< in: offset of the MySQL log info field in
				the trx sys header */
#ifdef WITH_WSREP
        trx_sysf_t*     sys_header, /*!< in: trx sys header */
#endif /* WITH_WSREP */
	mtr_t*		mtr);	/*!< in: mtr */
/*****************************************************************//**
Prints to stderr the MySQL binlog offset info in the trx system header if
the magic number shows it valid. */
UNIV_INTERN
void
trx_sys_print_mysql_binlog_offset(void);
/*===================================*/
#ifdef WITH_WSREP
/** Update WSREP checkpoint XID in sys header. */
void
trx_sys_update_wsrep_checkpoint(
        const XID*      xid,         /*!< in: WSREP XID */
        trx_sysf_t*     sys_header,  /*!< in: sys_header */
        mtr_t*          mtr);        /*!< in: mtr       */

void
/** Read WSREP checkpoint XID from sys header. */
trx_sys_read_wsrep_checkpoint(
        XID* xid); /*!< out: WSREP XID */
#endif /* WITH_WSREP */
/*****************************************************************//**
Prints to stderr the MySQL master log offset info in the trx system header if
the magic number shows it valid. */
UNIV_INTERN
void
trx_sys_print_mysql_master_log_pos(void);
/*====================================*/
/*****************************************************************//**
Initializes the tablespace tag system. */
UNIV_INTERN
void
trx_sys_file_format_init(void);
/*==========================*/
/*****************************************************************//**
Closes the tablespace tag system. */
UNIV_INTERN
void
trx_sys_file_format_close(void);
/*===========================*/
/********************************************************************//**
Tags the system table space with minimum format id if it has not been
tagged yet.
WARNING: This function is only called during the startup and AFTER the
redo log application during recovery has finished. */
UNIV_INTERN
void
trx_sys_file_format_tag_init(void);
/*==============================*/
/*****************************************************************//**
Shutdown/Close the transaction system. */
UNIV_INTERN
void
trx_sys_close(void);
/*===============*/
/*****************************************************************//**
Get the name representation of the file format from its id.
@return	pointer to the name */
UNIV_INTERN
const char*
trx_sys_file_format_id_to_name(
/*===========================*/
	const ulint	id);		/*!< in: id of the file format */
/*****************************************************************//**
Set the file format id unconditionally except if it's already the
same value.
@return	TRUE if value updated */
UNIV_INTERN
ibool
trx_sys_file_format_max_set(
/*========================*/
	ulint		format_id,	/*!< in: file format id */
	const char**	name);		/*!< out: max file format name or
					NULL if not needed. */
/*********************************************************************
Creates the rollback segments
@return number of rollback segments that are active. */
UNIV_INTERN
ulint
trx_sys_create_rsegs(
/*=================*/
	ulint	n_spaces,	/*!< number of tablespaces for UNDO logs */
	ulint	n_rsegs);	/*!< number of rollback segments to create */
/*****************************************************************//**
Get the number of transaction in the system, independent of their state.
@return count of transactions in trx_sys_t::trx_list */
UNIV_INLINE
ulint
trx_sys_get_n_rw_trx(void);
/*======================*/

/*********************************************************************
Check if there are any active (non-prepared) transactions.
@return total number of active transactions or 0 if none */
UNIV_INTERN
ulint
trx_sys_any_active_transactions(void);
/*=================================*/
#else /* !UNIV_HOTBACKUP */
/*****************************************************************//**
Prints to stderr the MySQL binlog info in the system header if the
magic number shows it valid. */
UNIV_INTERN
void
trx_sys_print_mysql_binlog_offset_from_page(
/*========================================*/
	const byte*	page);	/*!< in: buffer containing the trx
				system header page, i.e., page number
				TRX_SYS_PAGE_NO in the tablespace */
/*****************************************************************//**
Reads the file format id from the first system table space file.
Even if the call succeeds and returns TRUE, the returned format id
may be ULINT_UNDEFINED signalling that the format id was not present
in the data file.
@return TRUE if call succeeds */
UNIV_INTERN
ibool
trx_sys_read_file_format_id(
/*========================*/
	const char *pathname,	/*!< in: pathname of the first system
				table space file */
	ulint *format_id);	/*!< out: file format of the system table
				space */
/*****************************************************************//**
Reads the file format id from the given per-table data file.
@return TRUE if call succeeds */
UNIV_INTERN
ibool
trx_sys_read_pertable_file_format_id(
/*=================================*/
	const char *pathname,	/*!< in: pathname of a per-table
				datafile */
	ulint *format_id);	/*!< out: file format of the per-table
				data file */
#endif /* !UNIV_HOTBACKUP */
/*****************************************************************//**
Get the name representation of the file format from its id.
@return	pointer to the max format name */
UNIV_INTERN
const char*
trx_sys_file_format_max_get(void);
/*=============================*/
/*****************************************************************//**
Check for the max file format tag stored on disk.
@return	DB_SUCCESS or error code */
UNIV_INTERN
dberr_t
trx_sys_file_format_max_check(
/*==========================*/
	ulint		max_format_id);	/*!< in: the max format id to check */
/********************************************************************//**
Update the file format tag in the system tablespace only if the given
format id is greater than the known max id.
@return	TRUE if format_id was bigger than the known max id */
UNIV_INTERN
ibool
trx_sys_file_format_max_upgrade(
/*============================*/
	const char**	name,		/*!< out: max file format name */
	ulint		format_id);	/*!< in: file format identifier */
/*****************************************************************//**
Get the name representation of the file format from its id.
@return	pointer to the name */
UNIV_INTERN
const char*
trx_sys_file_format_id_to_name(
/*===========================*/
	const ulint	id);	/*!< in: id of the file format */

#ifdef UNIV_DEBUG
/*************************************************************//**
Validate the trx_sys_t::trx_list. */
UNIV_INTERN
ibool
trx_sys_validate_trx_list(void);
/*===========================*/
#endif /* UNIV_DEBUG */

/* The automatically created system rollback segment has this id */
#define TRX_SYS_SYSTEM_RSEG_ID	0

/* Space id and page no where the trx system file copy resides */
#define	TRX_SYS_SPACE	0	/* the SYSTEM tablespace */
#include "fsp0fsp.h"
#define	TRX_SYS_PAGE_NO	FSP_TRX_SYS_PAGE_NO

/* The offset of the transaction system header on the page */
#define	TRX_SYS		FSEG_PAGE_DATA

/** Transaction system header */
/*------------------------------------------------------------- @{ */
#define	TRX_SYS_TRX_ID_STORE	0	/*!< the maximum trx id or trx
					number modulo
					TRX_SYS_TRX_ID_UPDATE_MARGIN
					written to a file page by any
					transaction; the assignment of
					transaction ids continues from
					this number rounded up by
					TRX_SYS_TRX_ID_UPDATE_MARGIN
					plus
					TRX_SYS_TRX_ID_UPDATE_MARGIN
					when the database is
					started */
#define TRX_SYS_FSEG_HEADER	8	/*!< segment header for the
					tablespace segment the trx
					system is created into */
#define	TRX_SYS_RSEGS		(8 + FSEG_HEADER_SIZE)
					/*!< the start of the array of
					rollback segment specification
					slots */
/*------------------------------------------------------------- @} */

/* Max number of rollback segments: the number of segment specification slots
in the transaction system array; rollback segment id must fit in one (signed)
byte, therefore 128; each slot is currently 8 bytes in size. If you want
to raise the level to 256 then you will need to fix some assertions that
impose the 7 bit restriction. e.g., mach_write_to_3() */
#define	TRX_SYS_N_RSEGS			128
/* Originally, InnoDB defined TRX_SYS_N_RSEGS as 256 but created only one
rollback segment.  It initialized some arrays with this number of entries.
We must remember this limit in order to keep file compatibility. */
#define TRX_SYS_OLD_N_RSEGS		256

/** Maximum length of MySQL binlog file name, in bytes.
@see trx_sys_mysql_master_log_name
@see trx_sys_mysql_bin_log_name */
#define TRX_SYS_MYSQL_LOG_NAME_LEN	512
/** Contents of TRX_SYS_MYSQL_LOG_MAGIC_N_FLD */
#define TRX_SYS_MYSQL_LOG_MAGIC_N	873422344

#if UNIV_PAGE_SIZE_MIN < 4096
# error "UNIV_PAGE_SIZE_MIN < 4096"
#endif
/** The offset of the MySQL replication info in the trx system header;
this contains the same fields as TRX_SYS_MYSQL_LOG_INFO below */
#define TRX_SYS_MYSQL_MASTER_LOG_INFO	(UNIV_PAGE_SIZE - 2000)

/** The offset of the MySQL binlog offset info in the trx system header */
#define TRX_SYS_MYSQL_LOG_INFO		(UNIV_PAGE_SIZE - 1000)
#define	TRX_SYS_MYSQL_LOG_MAGIC_N_FLD	0	/*!< magic number which is
						TRX_SYS_MYSQL_LOG_MAGIC_N
						if we have valid data in the
						MySQL binlog info */
#define TRX_SYS_MYSQL_LOG_OFFSET_HIGH	4	/*!< high 4 bytes of the offset
						within that file */
#define TRX_SYS_MYSQL_LOG_OFFSET_LOW	8	/*!< low 4 bytes of the offset
						within that file */
#define TRX_SYS_MYSQL_LOG_NAME		12	/*!< MySQL log file name */

#ifdef WITH_WSREP
/* The offset to WSREP XID headers */
#define TRX_SYS_WSREP_XID_INFO (UNIV_PAGE_SIZE - 3500)
#define TRX_SYS_WSREP_XID_MAGIC_N_FLD 0
#define TRX_SYS_WSREP_XID_MAGIC_N 0x77737265

/* XID field: formatID, gtrid_len, bqual_len, xid_data */
#define TRX_SYS_WSREP_XID_LEN        (4 + 4 + 4 + XIDDATASIZE)
#define TRX_SYS_WSREP_XID_FORMAT     4
#define TRX_SYS_WSREP_XID_GTRID_LEN  8
#define TRX_SYS_WSREP_XID_BQUAL_LEN 12
#define TRX_SYS_WSREP_XID_DATA      16
#endif /* WITH_WSREP*/

/** Doublewrite buffer */
/* @{ */
/** The offset of the doublewrite buffer header on the trx system header page */
#define TRX_SYS_DOUBLEWRITE		(UNIV_PAGE_SIZE - 200)
/*-------------------------------------------------------------*/
#define TRX_SYS_DOUBLEWRITE_FSEG	0	/*!< fseg header of the fseg
						containing the doublewrite
						buffer */
#define TRX_SYS_DOUBLEWRITE_MAGIC	FSEG_HEADER_SIZE
						/*!< 4-byte magic number which
						shows if we already have
						created the doublewrite
						buffer */
#define TRX_SYS_DOUBLEWRITE_BLOCK1	(4 + FSEG_HEADER_SIZE)
						/*!< page number of the
						first page in the first
						sequence of 64
						(= FSP_EXTENT_SIZE) consecutive
						pages in the doublewrite
						buffer */
#define TRX_SYS_DOUBLEWRITE_BLOCK2	(8 + FSEG_HEADER_SIZE)
						/*!< page number of the
						first page in the second
						sequence of 64 consecutive
						pages in the doublewrite
						buffer */
#define TRX_SYS_DOUBLEWRITE_REPEAT	12	/*!< we repeat
						TRX_SYS_DOUBLEWRITE_MAGIC,
						TRX_SYS_DOUBLEWRITE_BLOCK1,
						TRX_SYS_DOUBLEWRITE_BLOCK2
						so that if the trx sys
						header is half-written
						to disk, we still may
						be able to recover the
						information */
/** If this is not yet set to TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED_N,
we must reset the doublewrite buffer, because starting from 4.1.x the
space id of a data page is stored into
FIL_PAGE_ARCH_LOG_NO_OR_SPACE_ID. */
#define TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED (24 + FSEG_HEADER_SIZE)

/*-------------------------------------------------------------*/
/** Contents of TRX_SYS_DOUBLEWRITE_MAGIC */
#define TRX_SYS_DOUBLEWRITE_MAGIC_N	536853855
/** Contents of TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED */
#define TRX_SYS_DOUBLEWRITE_SPACE_ID_STORED_N 1783657386

/** Size of the doublewrite block in pages */
#define TRX_SYS_DOUBLEWRITE_BLOCK_SIZE	FSP_EXTENT_SIZE
/* @} */

/** File format tag */
/* @{ */
/** The offset of the file format tag on the trx system header page
(TRX_SYS_PAGE_NO of TRX_SYS_SPACE) */
#define TRX_SYS_FILE_FORMAT_TAG		(UNIV_PAGE_SIZE - 16)

/** Contents of TRX_SYS_FILE_FORMAT_TAG when valid. The file format
identifier is added to this constant. */
#define TRX_SYS_FILE_FORMAT_TAG_MAGIC_N_LOW	3645922177UL
/** Contents of TRX_SYS_FILE_FORMAT_TAG+4 when valid */
#define TRX_SYS_FILE_FORMAT_TAG_MAGIC_N_HIGH	2745987765UL
/** Contents of TRX_SYS_FILE_FORMAT_TAG when valid. The file format
identifier is added to this 64-bit constant. */
#define TRX_SYS_FILE_FORMAT_TAG_MAGIC_N					\
	((ib_uint64_t) TRX_SYS_FILE_FORMAT_TAG_MAGIC_N_HIGH << 32	\
	 | TRX_SYS_FILE_FORMAT_TAG_MAGIC_N_LOW)
/* @} */

#ifndef UNIV_HOTBACKUP
/** The transaction system central memory data structure. */
struct trx_sys_t{

	ib_mutex_t		mutex;		/*!< mutex protecting most fields in
					this structure except when noted
					otherwise */
	ulint		n_prepared_trx;	/*!< Number of transactions currently
					in the XA PREPARED state */
	ulint		n_prepared_recovered_trx; /*!< Number of transactions
					currently in XA PREPARED state that are
					also recovered. Such transactions cannot
					be added during runtime. They can only
					occur after recovery if mysqld crashed
					while there were XA PREPARED
					transactions. We disable query cache
					if such transactions exist. */
	trx_id_t	max_trx_id;	/*!< The smallest number not yet
					assigned as a transaction id or
					transaction number */
#ifdef UNIV_DEBUG
	trx_id_t	rw_max_trx_id;	/*!< Max trx id of read-write transactions
					which exist or existed */
#endif
	trx_list_t	rw_trx_list;	/*!< List of active and committed in
					memory read-write transactions, sorted
					on trx id, biggest first. Recovered
					transactions are always on this list. */
	trx_list_t	ro_trx_list;	/*!< List of active and committed in
					memory read-only transactions, sorted
					on trx id, biggest first. NOTE:
					The order for read-only transactions
					is not necessary. We should exploit
					this and increase concurrency during
					add/remove. */
	trx_list_t	mysql_trx_list;	/*!< List of transactions created
					for MySQL. All transactions on
					ro_trx_list are on mysql_trx_list. The
					rw_trx_list can contain system
					transactions and recovered transactions
					that will not be in the mysql_trx_list.
					There can be active non-locking
					auto-commit read only transactions that
					are on this list but not on ro_trx_list.
					mysql_trx_list may additionally contain
					transactions that have not yet been
					started in InnoDB. */
	trx_rseg_t*	const rseg_array[TRX_SYS_N_RSEGS];
					/*!< Pointer array to rollback
					segments; NULL if slot not in use;
					created and destroyed in
					single-threaded mode; not protected
					by any mutex, because it is read-only
					during multi-threaded operation */
	ulint		rseg_history_len;/*!< Length of the TRX_RSEG_HISTORY
					list (update undo logs for committed
					transactions), protected by
					rseg->mutex */
	UT_LIST_BASE_NODE_T(read_view_t) view_list;
					/*!< List of read views sorted
					on trx no, biggest first */
};

/** When a trx id which is zero modulo this number (which must be a power of
two) is assigned, the field TRX_SYS_TRX_ID_STORE on the transaction system
page is updated */
#define TRX_SYS_TRX_ID_WRITE_MARGIN	256
#endif /* !UNIV_HOTBACKUP */

#ifndef UNIV_NONINL
#include "trx0sys.ic"
#endif

#endif