Device Characteristics

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## SQLite C Interface

## Device Characteristics

>     #define SQLITE_IOCAP_ATOMIC                 0x00000001
>     #define SQLITE_IOCAP_ATOMIC512              0x00000002
>     #define SQLITE_IOCAP_ATOMIC1K               0x00000004
>     #define SQLITE_IOCAP_ATOMIC2K               0x00000008
>     #define SQLITE_IOCAP_ATOMIC4K               0x00000010
>     #define SQLITE_IOCAP_ATOMIC8K               0x00000020
>     #define SQLITE_IOCAP_ATOMIC16K              0x00000040
>     #define SQLITE_IOCAP_ATOMIC32K              0x00000080
>     #define SQLITE_IOCAP_ATOMIC64K              0x00000100
>     #define SQLITE_IOCAP_SAFE_APPEND            0x00000200
>     #define SQLITE_IOCAP_SEQUENTIAL             0x00000400
>     #define SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN  0x00000800
>     #define SQLITE_IOCAP_POWERSAFE_OVERWRITE    0x00001000
>     #define SQLITE_IOCAP_IMMUTABLE              0x00002000
>     #define SQLITE_IOCAP_BATCH_ATOMIC           0x00004000
>     #define SQLITE_IOCAP_SUBPAGE_READ           0x00008000

The xDeviceCharacteristics method of the sqlite3_io_methods object returns an integer which is a vector of these bit values expressing I/O characteristics of the mass storage device that holds the file that the sqlite3_io_methods refers to.

The SQLITE_IOCAP_ATOMIC property means that all writes of any size are atomic. The SQLITE_IOCAP_ATOMICnnn values mean that writes of blocks that are nnn bytes in size and are aligned to an address which is an integer multiple of nnn are atomic. The SQLITE_IOCAP_SAFE_APPEND value means that when data is appended to a file, the data is appended first then the size of the file is extended, never the other way around. The SQLITE_IOCAP_SEQUENTIAL property means that information is written to disk in the same order as calls to xWrite(). The SQLITE_IOCAP_POWERSAFE_OVERWRITE property means that after reboot following a crash or power loss, the only bytes in a file that were written at the application level might have changed and that adjacent bytes, even bytes within the same sector are guaranteed to be unchanged. The SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN flag indicates that a file cannot be deleted when open. The SQLITE_IOCAP_IMMUTABLE flag indicates that the file is on read-only media and cannot be changed even by processes with elevated privileges.

The SQLITE_IOCAP_BATCH_ATOMIC property means that the underlying filesystem supports doing multiple write operations atomically when those write operations are bracketed by SQLITE_FCNTL_BEGIN_ATOMIC_WRITE and SQLITE_FCNTL_COMMIT_ATOMIC_WRITE.

The SQLITE_IOCAP_SUBPAGE_READ property means that it is ok to read from the database file in amounts that are not a multiple of the page size and that do not begin at a page boundary. Without this property, SQLite is careful to only do full-page reads and write on aligned pages, with the one exception that it will do a sub-page read of the first page to access the database header.

See also lists of Objects, Constants, and Functions.