Unmanaged database environment. More...

#include <mdbx.h++>

Classes
struct	geometry
	Database geometry for size management. More...

struct	limits

struct	operate_options
	Operate options. More...

struct	operate_parameters
	Operate parameters. More...

struct	reader_info
	Reader information. More...

struct	reclaiming_options
	Garbage reclaiming options. More...

Public Types
enum	mode { readonly, write_file_io, write_mapped_io }
	Operation mode. More...

enum	durability { robust_synchronous, half_synchronous_weak_last, lazy_weak_tail, whole_fragile }
	Durability level. More...

enum	remove_mode { just_remove = MDBX_ENV_JUST_DELETE, ensure_unused = MDBX_ENV_ENSURE_UNUSED, wait_for_unused = MDBX_ENV_WAIT_FOR_UNUSED }
	Deletion modes for remove(). More...

using	stat = ::MDBX_stat
	Statistics for a database in the MDBX environment. More...

using	info = ::MDBX_envinfo
	Information about the environment. More...

Public Member Functions
MDBX_CXX11_CONSTEXPR	env () noexcept=default

	env (const env &) noexcept=default

env &	operator= (env &&other) noexcept

	env (env &&other) noexcept

	~env () noexcept

MDBX_CXX14_CONSTEXPR	operator bool () const noexcept

MDBX_CXX14_CONSTEXPR	operator const MDBX_env * () const

MDBX_CXX14_CONSTEXPR	operator MDBX_env * ()

env::operate_parameters	get_operation_parameters () const
	Returns current operation parameters. More...

env::mode	get_mode () const
	Returns current operation mode. More...

env::durability	get_durability () const
	Returns current durability mode. More...

env::reclaiming_options	get_reclaiming () const
	Returns current reclaiming options. More...

env::operate_options	get_options () const
	Returns current operate options. More...

bool	is_pristine () const
	Returns `true` for a freshly created database, but `false` if at least one transaction was committed. More...

bool	is_empty () const
	Checks whether the database is empty. More...

size_t	dbsize_min () const
	Returns the minimal database size in bytes for the environment. More...

size_t	dbsize_max () const
	Returns the maximal database size in bytes for the environment. More...

size_t	key_min (key_mode mode) const noexcept
	Returns the minimal key size in bytes for specified keys mode. More...

size_t	key_max (key_mode mode) const
	Returns the maximal key size in bytes for specified keys mode. More...

size_t	value_min (value_mode mode) const noexcept
	Returns the minimal value size in bytes for specified values mode. More...

size_t	value_max (value_mode mode) const
	Returns the maximal value size in bytes for specified values mode. More...

size_t	transaction_size_max () const
	Returns the maximal write transaction size (i.e. limit for summary volume of dirty pages) in bytes. More...

env &	copy (const MDBX_STD_FILESYSTEM_PATH &destination, bool compactify, bool force_dynamic_size=false)
	Make a copy (backup) of an existing environment to the specified path. More...

env &	copy (const ::std::string &destination, bool compactify, bool force_dynamic_size=false)

env &	copy (filehandle fd, bool compactify, bool force_dynamic_size=false)
	Copy an environment to the specified file descriptor. More...

stat	get_stat () const
	Returns snapshot statistics about the MDBX environment. More...

size_t	get_pagesize () const
	Returns pagesize of this MDBX environment. More...

info	get_info () const
	Return snapshot information about the MDBX environment. More...

stat	get_stat (const txn &) const
	Return statistics about the MDBX environment accordingly to the specified transaction. More...

info	get_info (const txn &) const
	Return information about the MDBX environment accordingly to the specified transaction. More...

filehandle	get_filehandle () const
	Returns the file descriptor for the DXB file of MDBX environment. More...

path	get_path () const
	Return the path that was used for opening the environment. More...

MDBX_env_flags_t	get_flags () const
	Returns environment flags. More...

unsigned	max_readers () const
	Returns the maximum number of threads/reader slots for the environment. More...

unsigned	max_maps () const
	Returns the maximum number of named databases for the environment. More...

void *	get_context () const noexcept
	Returns the application context associated with the environment. More...

env &	set_context (void *)
	Sets the application context associated with the environment. More...

env &	set_sync_threshold (size_t bytes)
	Sets threshold to force flush the data buffers to disk, for non-sync durability modes. More...

env &	set_sync_period (unsigned seconds_16dot16)
	Sets relative period since the last unsteady commit to force flush the data buffers to disk, for non-sync durability modes. More...

env &	set_sync_period (double seconds)
	Sets relative period since the last unsteady commit to force flush the data buffers to disk, for non-sync durability modes. More...

env &	alter_flags (MDBX_env_flags_t flags, bool on_off)
	Alter environment flags. More...

env &	set_geometry (const geometry &size)
	Set all size-related parameters of environment. More...

bool	sync_to_disk (bool force=true, bool nonblock=false)
	Flush the environment data buffers. More...

bool	poll_sync_to_disk ()
	Performs non-blocking polling of sync-to-disk thresholds. More...

void	close_map (const map_handle &)
	Close a key-value map (aka sub-database) handle. Normally unnecessary. More...

template<typename VISITOR >
int	enumerate_readers (VISITOR &visitor)
	Enumerate readers. More...

unsigned	check_readers ()
	Checks for stale readers in the lock table and return number of cleared slots. More...

env &	set_HandleSlowReaders (MDBX_hsr_func *)
	Sets a Handle-Slow-Readers callback to resolve database full/overflow issue due to a reader(s) which prevents the old data from being recycled. More...

MDBX_hsr_func *	get_HandleSlowReaders () const noexcept
	Returns the current Handle-Slow-Readers callback used to resolve database full/overflow issue due to a reader(s) which prevents the old data from being recycled. More...

txn_managed	start_read () const
	Starts read (read-only) transaction. More...

txn_managed	prepare_read () const
	Creates but not start read transaction. More...

txn_managed	start_write (bool dont_wait=false)
	Starts write (read-write) transaction. More...

txn_managed	try_start_write ()
	Tries to start write (read-write) transaction without blocking. More...

Static Public Member Functions
static size_t	default_pagesize () noexcept
	Returns default page size for current system/platform. More...

static bool	remove (const MDBX_STD_FILESYSTEM_PATH &, const remove_mode mode=just_remove)
	Removes the environment's files in a proper and multiprocess-safe way. More...

static bool	remove (const ::std::string &, const remove_mode mode=just_remove)

Protected Member Functions
MDBX_CXX11_CONSTEXPR	env (MDBX_env *ptr) noexcept

Protected Attributes
MDBX_env *	handle_ {nullptr}

Friends
class	txn

MDBX_CXX11_CONSTEXPR bool	operator== (const env &a, const env &b) noexcept

MDBX_CXX11_CONSTEXPR bool	operator!= (const env &a, const env &b) noexcept

Detailed Description

Unmanaged database environment.

Like other unmanaged classes, env allows copying and assignment for instances, but does not destroys the represented underlying object from the own class destructor.

An environment supports multiple key-value sub-databases (aka key-value spaces or tables), all residing in the same shared-memory map.

Member Typedef Documentation

◆ info

using mdbx::env::info = ::MDBX_envinfo

Information about the environment.

◆ stat

using mdbx::env::stat = ::MDBX_stat

Statistics for a database in the MDBX environment.

Member Enumeration Documentation

◆ durability

enum mdbx::env::durability

Durability level.

Enumerator
robust_synchronous	Default robust and durable sync mode. Metadata is written and flushed to disk after a data is written and flushed, which guarantees the integrity of the database in the event of a crash at any time. Attention Please do not use other modes until you have studied all the details and are sure. Otherwise, you may lose your users' data, as happens in Miranda NG messenger.
half_synchronous_weak_last	Don't sync the meta-page after commit. Flush system buffers to disk only once per transaction commit, omit the metadata flush. Defer that until the system flushes files to disk, or next non-MDBX_RDONLY commit or mdbx_env_sync(). Depending on the platform and hardware, with MDBX_NOMETASYNC you may get a doubling of write performance. This trade-off maintains database integrity, but a system crash may undo the last committed transaction. I.e. it preserves the ACI (atomicity, consistency, isolation) but not D (durability) database property. `MDBX_NOMETASYNC` flag may be changed at any time using mdbx_env_set_flags() or by passing to mdbx_txn_begin() for particular write transaction. See also SYNC MODES
lazy_weak_tail	Don't sync anything but keep previous steady commits. Like MDBX_UTTERLY_NOSYNC the `MDBX_SAFE_NOSYNC` flag disable similarly flush system buffers to disk when committing a transaction. But there is a huge difference in how are recycled the MVCC snapshots corresponding to previous "steady" transactions (see below). With MDBX_WRITEMAP the `MDBX_SAFE_NOSYNC` instructs MDBX to use asynchronous mmap-flushes to disk. Asynchronous mmap-flushes means that actually all writes will scheduled and performed by operation system on it own manner, i.e. unordered. MDBX itself just notify operating system that it would be nice to write data to disk, but no more. Depending on the platform and hardware, with `MDBX_SAFE_NOSYNC` you may get a multiple increase of write performance, even 10 times or more. In contrast to MDBX_UTTERLY_NOSYNC mode, with `MDBX_SAFE_NOSYNC` flag MDBX will keeps untouched pages within B-tree of the last transaction "steady" which was synced to disk completely. This has big implications for both data durability and (unfortunately) performance: a system crash can't corrupt the database, but you will lose the last transactions; because MDBX will rollback to last steady commit since it kept explicitly. the last steady transaction makes an effect similar to "long-lived" read transaction (see above in the Restrictions & Caveats section) since prevents reuse of pages freed by newer write transactions, thus the any data changes will be placed in newly allocated pages. to avoid rapid database growth, the system will sync data and issue a steady commit-point to resume reuse pages, each time there is insufficient space and before increasing the size of the file on disk. In other words, with `MDBX_SAFE_NOSYNC` flag MDBX insures you from the whole database corruption, at the cost increasing database size and/or number of disk IOPs. So, `MDBX_SAFE_NOSYNC` flag could be used with mdbx_env_sync() as alternatively for batch committing or nested transaction (in some cases). As well, auto-sync feature exposed by mdbx_env_set_syncbytes() and mdbx_env_set_syncperiod() functions could be very useful with `MDBX_SAFE_NOSYNC` flag. The number and volume of of disk IOPs with MDBX_SAFE_NOSYNC flag will exactly the as without any no-sync flags. However, you should expect a larger process's work set and significantly worse a locality of reference, due to the more intensive allocation of previously unused pages and increase the size of the database. `MDBX_SAFE_NOSYNC` flag may be changed at any time using mdbx_env_set_flags() or by passing to mdbx_txn_begin() for particular write transaction.
whole_fragile	Don't sync anything and wipe previous steady commits. Don't flush system buffers to disk when committing a transaction. This optimization means a system crash can corrupt the database, if buffers are not yet flushed to disk. Depending on the platform and hardware, with `MDBX_UTTERLY_NOSYNC` you may get a multiple increase of write performance, even 100 times or more. If the filesystem preserves write order (which is rare and never provided unless explicitly noted) and the MDBX_WRITEMAP and MDBX_LIFORECLAIM flags are not used, then a system crash can't corrupt the database, but you can lose the last transactions, if at least one buffer is not yet flushed to disk. The risk is governed by how often the system flushes dirty buffers to disk and how often mdbx_env_sync() is called. So, transactions exhibit ACI (atomicity, consistency, isolation) properties and only lose `D` (durability). I.e. database integrity is maintained, but a system crash may undo the final transactions. Otherwise, if the filesystem not preserves write order (which is typically) or MDBX_WRITEMAP or MDBX_LIFORECLAIM flags are used, you should expect the corrupted database after a system crash. So, most important thing about `MDBX_UTTERLY_NOSYNC`: a system crash immediately after commit the write transaction high likely lead to database corruption. successful completion of mdbx_env_sync(force = true) after one or more committed transactions guarantees consistency and durability. BUT by committing two or more transactions you back database into a weak state, in which a system crash may lead to database corruption! In case single transaction after mdbx_env_sync, you may lose transaction itself, but not a whole database. Nevertheless, `MDBX_UTTERLY_NOSYNC` provides "weak" durability in case of an application crash (but no durability on system failure), and therefore may be very useful in scenarios where data durability is not required over a system failure (e.g for short-lived data), or if you can take such risk. `MDBX_UTTERLY_NOSYNC` flag may be changed at any time using mdbx_env_set_flags(), but don't has effect if passed to mdbx_txn_begin() for particular write transaction. See also SYNC MODES

◆ mode

enum mdbx::env::mode

Operation mode.

Enumerator

readonly

Read only mode.

Open the environment in read-only mode. No write operations will be allowed. MDBX will still modify the lock file - except on read-only filesystems, where MDBX does not use locks.

with MDBX_RDONLY = open environment in read-only mode. MDBX supports pure read-only mode (i.e. without opening LCK-file) only when environment directory and/or both files are not writable (and the LCK-file may be missing). In such case allowing file(s) to be placed on a network read-only share.
without MDBX_RDONLY = open environment in read-write mode.

This flag affects only at environment opening but can't be changed after.

write_file_io

write_mapped_io

Map data into memory with write permission.

Use a writeable memory map unless MDBX_RDONLY is set. This uses fewer mallocs and requires much less work for tracking database pages, but loses protection from application bugs like wild pointer writes and other bad updates into the database. This may be slightly faster for DBs that fit entirely in RAM, but is slower for DBs larger than RAM. Also adds the possibility for stray application writes thru pointers to silently corrupt the database.

with MDBX_WRITEMAP = all data will be mapped into memory in the read-write mode. This offers a significant performance benefit, since the data will be modified directly in mapped memory and then flushed to disk by single system call, without any memory management nor copying.
without MDBX_WRITEMAP = data will be mapped into memory in the read-only mode. This requires stocking all modified database pages in memory and then writing them to disk through file operations.

Warning: On the other hand, MDBX_WRITEMAP adds the possibility for stray application writes thru pointers to silently corrupt the database.

Note: The MDBX_WRITEMAP mode is incompatible with nested transactions, since this is unreasonable. I.e. nested transactions requires mallocation of database pages and more work for tracking ones, which neuters a performance boost caused by the MDBX_WRITEMAP mode.

This flag affects only at environment opening but can't be changed after.

◆ remove_mode

enum mdbx::env::remove_mode

Deletion modes for remove().

Enumerator

just_remove

Just delete the environment's files and directory if any.

Note: On POSIX systems, processes already working with the database will continue to work without interference until it close the environment.; On Windows, the behavior of just_remove is different because the system does not support deleting files that are currently memory mapped.

ensure_unused

Make sure that the environment is not being used by other processes, or return an error otherwise.

wait_for_unused

Wait until other processes closes the environment before deletion.

Constructor & Destructor Documentation

◆ env() [1/4]

MDBX_CXX11_CONSTEXPR mdbx::env::env ( MDBX_env * ptr )

protectednoexcept

◆ env() [2/4]

MDBX_CXX11_CONSTEXPR mdbx::env::env ( )

defaultnoexcept

◆ env() [3/4]

mdbx::env::env ( const env & )

defaultnoexcept

◆ env() [4/4]

mdbx::env::env ( env && other )

inlinenoexcept

◆ ~env()

mdbx::env::~env ( )

inlinenoexcept

Member Function Documentation

◆ alter_flags()

env & mdbx::env::alter_flags	(	MDBX_env_flags_t	flags,
		bool	on_off
	)

inline

Alter environment flags.

◆ check_readers()

unsigned mdbx::env::check_readers ( )

inline

Checks for stale readers in the lock table and return number of cleared slots.

◆ close_map()

void mdbx::env::close_map ( const map_handle & handle )

inline

Close a key-value map (aka sub-database) handle. Normally unnecessary.

Closing a database handle is not necessary, but lets txn::open_map() reuse the handle value. Usually it's better to set a bigger env::operate_parameters::max_maps, unless that value would be large.

Note: Use with care. This call is synchronized via mutex with other calls close_map(), but NOT with other transactions running by other threads. The "next" version of libmdbx (MithrilDB) will solve this issue.

Handles should only be closed if no other threads are going to reference the database handle or one of its cursors any further. Do not close a handle if an existing transaction has modified its database. Doing so can cause misbehavior from database corruption to errors like MDBX_BAD_DBI (since the DB name is gone).

◆ copy() [1/3]

env& mdbx::env::copy	(	const ::std::string &	destination,
		bool	compactify,
		bool	force_dynamic_size = `false`
	)

◆ copy() [2/3]

env& mdbx::env::copy	(	const MDBX_STD_FILESYSTEM_PATH &	destination,
		bool	compactify,
		bool	force_dynamic_size = `false`
	)

Make a copy (backup) of an existing environment to the specified path.

◆ copy() [3/3]

env& mdbx::env::copy	(	filehandle	fd,
		bool	compactify,
		bool	force_dynamic_size = `false`
	)

Copy an environment to the specified file descriptor.

◆ dbsize_max()

size_t mdbx::env::dbsize_max ( ) const

inline

Returns the maximal database size in bytes for the environment.

◆ dbsize_min()

size_t mdbx::env::dbsize_min ( ) const

inline

Returns the minimal database size in bytes for the environment.

◆ default_pagesize()

static size_t mdbx::env::default_pagesize ( )

inlinestaticnoexcept

Returns default page size for current system/platform.

◆ enumerate_readers()

template<typename VISITOR >

int mdbx::env::enumerate_readers ( VISITOR & visitor )

inline

Enumerate readers.

The VISITOR class must have int operator(const reader_info&, int serial) which should return continue_loop (zero) to continue enumeration, or any non-zero value to exit.

Returns: The last value returned from visitor' functor.

◆ get_context()

void * mdbx::env::get_context ( ) const

inlinenoexcept

Returns the application context associated with the environment.

◆ get_durability()

env::durability mdbx::env::get_durability ( ) const

inline

Returns current durability mode.

◆ get_filehandle()

filehandle mdbx::env::get_filehandle ( ) const

inline

Returns the file descriptor for the DXB file of MDBX environment.

◆ get_flags()

MDBX_env_flags_t mdbx::env::get_flags ( ) const

inline

Returns environment flags.

◆ get_HandleSlowReaders()

MDBX_hsr_func * mdbx::env::get_HandleSlowReaders ( ) const

inlinenoexcept

Returns the current Handle-Slow-Readers callback used to resolve database full/overflow issue due to a reader(s) which prevents the old data from being recycled.

See also: set_HandleSlowReaders()

◆ get_info() [1/2]

env::info mdbx::env::get_info ( ) const

inline

Return snapshot information about the MDBX environment.

◆ get_info() [2/2]

env::info mdbx::env::get_info ( const txn & txn ) const

inline

Return information about the MDBX environment accordingly to the specified transaction.

◆ get_mode()

env::mode mdbx::env::get_mode ( ) const

inline

Returns current operation mode.

◆ get_operation_parameters()

env::operate_parameters mdbx::env::get_operation_parameters ( ) const

inline

Returns current operation parameters.

◆ get_options()

env::operate_options mdbx::env::get_options ( ) const

inline

Returns current operate options.

◆ get_pagesize()

size_t mdbx::env::get_pagesize ( ) const

inline

Returns pagesize of this MDBX environment.

◆ get_path()

path mdbx::env::get_path ( ) const

Return the path that was used for opening the environment.

◆ get_reclaiming()

env::reclaiming_options mdbx::env::get_reclaiming ( ) const

inline

Returns current reclaiming options.

◆ get_stat() [1/2]

env::stat mdbx::env::get_stat ( ) const

inline

Returns snapshot statistics about the MDBX environment.

◆ get_stat() [2/2]

env::stat mdbx::env::get_stat ( const txn & txn ) const

inline

Return statistics about the MDBX environment accordingly to the specified transaction.

◆ is_empty()

bool mdbx::env::is_empty ( ) const

Checks whether the database is empty.

◆ is_pristine()

bool mdbx::env::is_pristine ( ) const

Returns true for a freshly created database, but false if at least one transaction was committed.

◆ key_max()

size_t mdbx::env::key_max ( key_mode mode ) const

inline

Returns the maximal key size in bytes for specified keys mode.

◆ key_min()

size_t mdbx::env::key_min ( key_mode mode ) const

inlinenoexcept

Returns the minimal key size in bytes for specified keys mode.

◆ max_maps()

unsigned mdbx::env::max_maps ( ) const

inline

Returns the maximum number of named databases for the environment.

◆ max_readers()

unsigned mdbx::env::max_readers ( ) const

inline

Returns the maximum number of threads/reader slots for the environment.

◆ operator bool()

MDBX_CXX14_CONSTEXPR mdbx::env::operator bool ( ) const

noexcept

◆ operator const MDBX_env *()

MDBX_CXX14_CONSTEXPR mdbx::env::operator const MDBX_env * ( ) const

◆ operator MDBX_env *()

MDBX_CXX14_CONSTEXPR mdbx::env::operator MDBX_env * ( )

◆ operator=()

env & mdbx::env::operator= ( env && other )

inlinenoexcept

◆ poll_sync_to_disk()

bool mdbx::env::poll_sync_to_disk ( )

inline

Performs non-blocking polling of sync-to-disk thresholds.

Returns: True if sync done or no data to sync, or false if the environment is busy by other thread or none of the thresholds are reached.

◆ prepare_read()

txn_managed mdbx::env::prepare_read ( ) const

inline

Creates but not start read transaction.

◆ remove() [1/2]

static bool mdbx::env::remove	(	const ::std::string &	,
		const remove_mode	mode = `just_remove`
	)

static

◆ remove() [2/2]

static bool mdbx::env::remove	(	const MDBX_STD_FILESYSTEM_PATH &	,
		const remove_mode	mode = `just_remove`
	)

static

Removes the environment's files in a proper and multiprocess-safe way.

◆ set_context()

env & mdbx::env::set_context ( void * ptr )

inline

Sets the application context associated with the environment.

◆ set_geometry()

env & mdbx::env::set_geometry ( const geometry & size )

inline

Set all size-related parameters of environment.

◆ set_HandleSlowReaders()

env & mdbx::env::set_HandleSlowReaders ( MDBX_hsr_func * cb )

inline

Sets a Handle-Slow-Readers callback to resolve database full/overflow issue due to a reader(s) which prevents the old data from being recycled.

Such callback will be triggered in a case where there is not enough free space in the database due to long read transaction(s) which impedes reusing the pages of an old MVCC snapshot(s).

Using this callback you can choose how to resolve the situation:

abort the write transaction with an error;
wait for the read transaction(s) to complete;
notify a thread performing a long-lived read transaction and wait for an effect;
kill the thread or whole process that performs the long-lived read transaction;

See also: long-lived-read

◆ set_sync_period() [1/2]

env & mdbx::env::set_sync_period ( double seconds )

inline

Sets relative period since the last unsteady commit to force flush the data buffers to disk, for non-sync durability modes.

The relative period value affects all processes which operates with given environment until the last process close environment or a new value will be settled. Data is always written to disk when txn_managed::commit() is called, but the operating system may keep it buffered. MDBX always flushes the OS buffers upon commit as well, unless the environment was opened with whole_fragile, lazy_weak_tail or in part half_synchronous_weak_last. Settled period don't checked asynchronously, but only by the txn_managed::commit() and env::sync_to_disk() functions. Therefore, in cases where transactions are committed infrequently and/or irregularly, polling by env::poll_sync_to_disk() may be a reasonable solution to timeout enforcement. The default is 0, than mean no any timeout checked, and no additional flush will be made.

Parameters

[in] seconds The period in second when a synchronous flush would be made since the last unsteady commit.

◆ set_sync_period() [2/2]

env & mdbx::env::set_sync_period ( unsigned seconds_16dot16 )

inline

Sets relative period since the last unsteady commit to force flush the data buffers to disk, for non-sync durability modes.

The relative period value affects all processes which operates with given environment until the last process close environment or a new value will be settled. Data is always written to disk when txn_managed::commit() is called, but the operating system may keep it buffered. MDBX always flushes the OS buffers upon commit as well, unless the environment was opened with whole_fragile, lazy_weak_tail or in part half_synchronous_weak_last. Settled period don't checked asynchronously, but only by the txn_managed::commit() and env::sync_to_disk() functions. Therefore, in cases where transactions are committed infrequently and/or irregularly, polling by env::poll_sync_to_disk() may be a reasonable solution to timeout enforcement. The default is 0, than mean no any timeout checked, and no additional flush will be made.

Parameters

[in] seconds_16dot16 The period in 1/65536 of second when a synchronous flush would be made since the last unsteady commit.

◆ set_sync_threshold()

env & mdbx::env::set_sync_threshold ( size_t bytes )

inline

Sets threshold to force flush the data buffers to disk, for non-sync durability modes.

The threshold value affects all processes which operates with given environment until the last process close environment or a new value will be settled. Data is always written to disk when txn_managed::commit() is called, but the operating system may keep it buffered. MDBX always flushes the OS buffers upon commit as well, unless the environment was opened with whole_fragile, lazy_weak_tail or in part half_synchronous_weak_last. The default is 0, than mean no any threshold checked, and no additional flush will be made.

◆ start_read()

txn_managed mdbx::env::start_read ( ) const

inline

Starts read (read-only) transaction.

◆ start_write()

txn_managed mdbx::env::start_write ( bool dont_wait = false )

inline

Starts write (read-write) transaction.

◆ sync_to_disk()

bool mdbx::env::sync_to_disk	(	bool	force = `true`,
		bool	nonblock = `false`
	)

inline

Flush the environment data buffers.

Returns: True if sync done or no data to sync, or false if the environment is busy by other thread or none of the thresholds are reached.

◆ transaction_size_max()

size_t mdbx::env::transaction_size_max ( ) const

inline

Returns the maximal write transaction size (i.e. limit for summary volume of dirty pages) in bytes.

◆ try_start_write()

txn_managed mdbx::env::try_start_write ( )

inline

Tries to start write (read-write) transaction without blocking.

◆ value_max()

size_t mdbx::env::value_max ( value_mode mode ) const

inline

Returns the maximal value size in bytes for specified values mode.

◆ value_min()

size_t mdbx::env::value_min ( value_mode mode ) const

inlinenoexcept

Returns the minimal value size in bytes for specified values mode.

Friends And Related Function Documentation

◆ operator!=

MDBX_CXX11_CONSTEXPR bool operator!=	(	const env &	a,
		const env &	b
	)

friend

◆ operator==

MDBX_CXX11_CONSTEXPR bool operator==	(	const env &	a,
		const env &	b
	)

friend

◆ txn

friend class txn

friend

Member Data Documentation

◆ handle_

MDBX_env* mdbx::env::handle_ {nullptr}

protected

The documentation for this class was generated from the following file:

mdbx.h++

Classes

Public Types

Public Member Functions

Static Public Member Functions

Protected Member Functions

Protected Attributes

Friends

Detailed Description

Member Typedef Documentation

◆ info

◆ stat

Member Enumeration Documentation

◆ durability

◆ mode

◆ remove_mode

Constructor & Destructor Documentation

◆ env() [1/4]

◆ env() [2/4]

◆ env() [3/4]

◆ env() [4/4]

◆ ~env()

Member Function Documentation

◆ alter_flags()

◆ check_readers()

◆ close_map()

◆ copy() [1/3]

◆ copy() [2/3]

◆ copy() [3/3]

◆ dbsize_max()

◆ dbsize_min()

◆ default_pagesize()

◆ enumerate_readers()

◆ get_context()

◆ get_durability()

◆ get_filehandle()

◆ get_flags()

◆ get_HandleSlowReaders()

◆ get_info() [1/2]

◆ get_info() [2/2]

◆ get_mode()

◆ get_operation_parameters()

◆ get_options()

◆ get_pagesize()

◆ get_path()

◆ get_reclaiming()

◆ get_stat() [1/2]

◆ get_stat() [2/2]

◆ is_empty()

◆ is_pristine()

◆ key_max()

◆ key_min()

◆ max_maps()

◆ max_readers()

◆ operator bool()

◆ operator const MDBX_env *()

◆ operator MDBX_env *()

◆ operator=()

◆ poll_sync_to_disk()

◆ prepare_read()

◆ remove() [1/2]

◆ remove() [2/2]

◆ set_context()

◆ set_geometry()

◆ set_HandleSlowReaders()

◆ set_sync_period() [1/2]

◆ set_sync_period() [2/2]

◆ set_sync_threshold()

◆ start_read()

◆ start_write()

◆ sync_to_disk()

◆ transaction_size_max()

◆ try_start_write()

◆ value_max()

◆ value_min()

Friends And Related Function Documentation

◆ operator!=

◆ operator==

◆ txn

Member Data Documentation

◆ handle_