Module lmdb_zero::open
[−]
[src]
Flags used when opening an LMDB environment.
Structs
Flags |
Flags used when opening an LMDB environment. |
Constants
FIXEDMAP |
Use a fixed address for the mmap region. This flag must be specified when creating the environment, and is stored persistently in the environment. If successful, the memory map will always reside at the same virtual address and pointers used to reference data items in the database will be constant across multiple invocations. This option may not always work, depending on how the operating system has allocated memory to shared libraries and other uses. The feature is highly experimental. |
MAPASYNC |
When using |
NOLOCK |
Don't do any locking. If concurrent access is anticipated, the caller must manage all concurrency itself. For proper operation the caller must enforce single-writer semantics, and must ensure that no readers are using old transactions while a writer is active. The simplest approach is to use an exclusive lock so that no readers may be active at all when a writer begins. |
NOMEMINIT |
Don't initialize malloc'd memory before writing to unused
spaces in the data file. By default, memory for pages written
to the data file is obtained using malloc. While these pages
may be reused in subsequent transactions, freshly malloc'd
pages will be initialized to zeroes before use. This avoids
persisting leftover data from other code (that used the heap
and subsequently freed the memory) into the data file. Note
that many other system libraries may allocate and free memory
from the heap for arbitrary uses. E.g., stdio may use the heap
for file I/O buffers. This initialization step has a modest
performance cost so some applications may want to disable it
using this flag. This option can be a problem for applications
which handle sensitive data like passwords, and it makes memory
checkers like Valgrind noisy. This flag is not needed with
|
NOMETASYNC |
Flush system buffers to disk only once per transaction, omit
the metadata flush. Defer that until the system flushes files
to disk, or next non- |
NORDAHEAD |
Turn off readahead. Most operating systems perform readahead on read requests by default. This option turns it off if the OS supports it. Turning it off may help random read performance when the DB is larger than RAM and system RAM is full. The option is not implemented on Windows. |
NOSUBDIR |
By default, LMDB creates its environment in a directory whose
pathname is given in path, and creates its data and lock files
under that directory. With this option, the |
NOSYNC |
Don't flush system buffers to disk when committing a
transaction. This optimization means a system crash can corrupt
the database or lose the last transactions if buffers are not
yet flushed to disk. The risk is governed by how often the
system flushes dirty buffers to disk and how often
|
NOTLS |
Don't use Thread-Local Storage. Tie reader locktable slots to
transaction objects instead of to threads. I.e.
|
RDONLY |
Open the environment in read-only mode. No write operations will be allowed. LMDB will still modify the lock file - except on read-only filesystems, where LMDB does not use locks. |
WRITEMAP |
Use a writeable memory map unless |