hdfsOpenFile2()

Supported by libMapRClient for hadoop-2.x

Opens a file in a given mode. Creates the file if the file does not exist.

If hdfsOpenFile2() creates a file, it stores the size of the name container in a location that you pass a pointer into, so that you can keep track of this size. The size is in bytes.

Keeping track of the size of the name container is useful when you are creating files that are less than or equal to 64 KB. When the size of all of the such files together for one name container exceeds 64 GB, operations on the name container can become inefficient. If the size of a name container reaches 64 GB, you can switch to a new or different volume.

Before the call to hdfsOpenFile2(), hdfsExists() can check that the file exists, if a check is needed.

After finishing work on a file, call hdfsCloseFile() to free the resources that are associated with the file.

Signature

hdfsFile hdfsOpenFile2(hdfsFS fs, const char* path, int flags, int bufferSize, short replication, tSize blocksize, tSize *nameSizeInBytes)

Parameters

Parameter Description
fs The handle of the filesystem where the file is located. Obtain this handle with one of the hdfsConnect() APIs.
path The full path to the file.
flags One of the following values. These flags are included in the fcntl.h header file.
O_RDONLY
Opens the file in read-only mode with the current offset at 0.
O_RDWR
Opens the file in read-write mode. If the file already exists, it is truncated to offset 0, effectively deleting the content of the file.
O_RDWR | O_APPEND
Opens the file in read-write mode with the current offset at 0. Writing to the file with hdfsWrite() appends the written data to the end of the file. Data written with hdfsPwrite() is not appended, but written starting at the offset specified in the call to that API.
O_WRONLY
Opens the file in write-only mode. If the file already exists, it is truncated to offset 0, effectively deleting the content of the file.
O_WRONLY | O_APPEND
Opens the file in write-only mode with the current offset at 0. Writing to the file with hdfsWrite() appends the written data to the end of the file. Data written with hdfsPwrite() is not appended, but written starting at the offset specified in the call to that API.
bufferSize Ignored for files on MapR file system
replication Ignored for files on MapR file system
blocksize The size of chunks for the file in bytes. Use 0 if you want to use the value that is specified for the fs.mapr.block.size parameter in the /opt/mapr/hadoop/hadoop-2.x/etc/hadoop/core-site.xml file on the client (if the client is using the libMapRClient version of hadoop-2.x). If this parameter is not set in core-site.xml, the default value is taken from the directory’s .dfs_attrributes file.
nameSizeInBytes A pointer to a memory buffer that can store the size in bytes of the name container. The value is returned only if hdfsOpenFile2() creates the specified file because the file does not already exist.

Return Value

Returns the handle to the open file or NULL on error.

Check errno for error codes and meanings.