MTBL_WRITER(3)

NAME
mtbl_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. No data may have been written to the file descriptor.

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, 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 VALUE

mtbl_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.