MTBL_WRITER(3)MTBL_WRITER(3)NAMEmtbl_writer - create an MTBL file
SYNOPSIS
#include <mtbl.h>
Writer objects:
struct mtbl_writer *
mtbl_writer_init(const char *fname, const struct mtbl_writer_options *wopt);
struct mtbl_writer *
mtbl_writer_init_fd(int fd, const struct mtbl_writer_options *wopt);
void
mtbl_writer_destroy(struct mtbl_writer **w);
mtbl_res
mtbl_writer_add(struct mtbl_writer *w,
const uint8_t *key, size_t len_key,
const uint8_t *val, size_t len_val);
Writer options:
struct mtbl_writer_options *
mtbl_writer_options_init(void);
void
mtbl_writer_options_destroy(struct mtbl_writer_options **wopt);
void
mtbl_writer_options_set_compression(
struct mtbl_writer_options *wopt,
mtbl_compression_type compression_type);
void
mtbl_writer_options_set_block_size(
struct mtbl_writer_options *wopt,
size_t block_size);
void
mtbl_writer_options_set_block_restart_interval(
struct mtbl_writer_options *wopt,
size_t block_restart_interval);
DESCRIPTION
MTBL files are written to disk by creating an mtbl_writer object,
calling mtbl_writer_add() for each key-value entry, and then calling
mtbl_writer_destroy().
mtbl_writer_add() copies key-value pairs from the caller into the
mtbl_writer object. Keys are specified as a pointer to a buffer, key,
and the length of that buffer, len_key. Values are specified as a
pointer to a buffer, val, and the length of that buffer, len_val.
Keys must be in sorted, lexicographical byte order. The same key may
not be added to an mtbl_writer more than once. If the input entries are
not sorted or may contain duplicate keys, then the mtbl_sorter(3)
interface should be used instead.
mtbl_writer objects may be created by calling mtbl_writer_init() with
an fname argument specifying a filename to be created. The filename
must not already exist on the filesystem. Or, mtbl_writer_init_fd() may
be called with an fd argument specifying an open, writable file
descriptor. Prior to the call, moving fd's cursor via write(2) or
lseek(2) will have the effect of reserving the file’s initial bytes for
non-MTBL use. MTBL will only write at, or above the current offset.
Thereafter, only mtbl_writer may access this fd (including closing it),
and no other writes may be made to the underlying file above the first
offset of the MTBL data. The MTBL data must be last in the file.
If the wopt parameter to mtbl_writer_init() or mtbl_writer_init_fd() is
non-NULL, the parameters specified in the mtbl_writer_options object
will be configured into the mtbl_writer object.
Writer options
compression
Specifies the compression algorithm to use on data blocks. Possible
values are MTBL_COMPRESSION_NONE, MTBL_COMPRESSION_SNAPPY,
MTBL_COMPRESSION_LZ4, MTBL_COMPRESSION_LZ4HC, or
MTBL_COMPRESSION_ZLIB (the default).
block_size
The maximum size of uncompressed data blocks, specified in bytes.
The default is 8 kilobytes.
block_restart_interval
How frequently to restart intra-block key prefix compression. The
default is every 16 keys.
RETURN VALUEmtbl_writer_init() and mtbl_writer_init_fd() return NULL on failure,
and non-NULL on success.
mtbl_writer_add() returns mtbl_res_success if the key-value entry was
successfully copied into the mtbl_writer object, and mtbl_res_failure
if not, for instance if there has been a key-ordering violation.
07/17/2015 MTBL_WRITER(3)
