Public Attributes
uint32_t	mtb_magic
uint32_t	mtb_format
volatile txnid_t	mtb_txnid
volatile unsigned	mtb_numreaders
mdb_mutex_t	mtb_rmutex

Detailed Description

The header for the reader table. The table resides in a memory-mapped file. (This is a different file than is used for the main database.)

For POSIX the actual mutexes reside in the shared memory of this mapped file. On Windows, mutexes are named objects allocated by the kernel; we store the mutex names in this mapped file so that other processes can grab them. This same approach is also used on MacOSX/Darwin (using named semaphores) since MacOSX doesn't support process-shared POSIX mutexes. For these cases where a named object is used, the object name is derived from a 64 bit FNV hash of the environment pathname. As such, naming collisions are extremely unlikely. If a collision occurs, the results are unpredictable.

Member Data Documentation

◆ mtb_format

uint32_t MDB_txbody::mtb_format

Format of this lock file. Must be set to MDB_LOCK_FORMAT.

◆ mtb_magic

uint32_t MDB_txbody::mtb_magic

Stamp identifying this as an LMDB file. It must be set to MDB_MAGIC.

◆ mtb_numreaders

volatile unsigned MDB_txbody::mtb_numreaders

The number of slots that have been used in the reader table. This always records the maximum count, it is not decremented when readers release their slots.

◆ mtb_rmutex

mdb_mutex_t MDB_txbody::mtb_rmutex

Mutex protecting access to this table. This is the reader table lock used with LOCK_MUTEX().

◆ mtb_txnid

volatile txnid_t MDB_txbody::mtb_txnid

The ID of the last transaction committed to the database. This is recorded here only for convenience; the value can always be determined by reading the main database meta pages.

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

external/db_drivers/liblmdb/mdb.c