SYNOPSIS

User-provided functions:

typedef void *
(*mtbl_merge_init_func)(void);

typedef void
(*mtbl_merge_free_func)(void *clos);

typedef void
(*mtbl_merge_func)(void *clos,
        const uint8_t *key, size_t len_key,
        const uint8_t *val0, size_t len_val0,
        const uint8_t *val1, size_t len_val1,
        uint8_t **merged_val, size_t *len_merged_val);

Command line tool:

export MTBL_MERGE_DSO="libexample.so.0"
export MTBL_MERGE_FUNC_PREFIX="example_merge"
mtbl_merge [-b SIZE] [-c COMPRESSION] INPUT [INPUT]... OUTPUT

DESCRIPTION

mtbl_merge(1) is a command-line driver for the mtbl_merger(3) interface. The mtbl_merger(3) interface requires a user-provided merge function, which is loaded from a shared object whose filename is specified in the environment variable MTBL_MERGE_DSO.

The user-provided merge function must have the same type as the mtbl_merge_func function type given above in the synopsis. The symbol name of the merge function to be loaded from the user-provided DSO will be constructed by appending "_func" to the string provided in the MTBL_MERGE_FUNC_PREFIX environment variable, which must be non-empty.

Additionally, two optional functions may be provided: an "init" function whose symbol name is "_init" appended to the function prefix, and a "free" function whose symbol name is "_free" appended to the function prefix. If the "init" function exists, it will be called at the beginning, before any calls to the merge function, and the return value from the init function will be passed as the first argument to the merge function. If the "free" function exists, it will be called at the end, after any calls to the merge function, and its argument will be the return value of the "init" function.

The environment variable MTBL_MERGE_BLOCK_SIZE may optionally be set in order to configure the MTBL block size (in bytes) of the output file.

OPTIONS

-b SIZE

The uncompressed data block size hint for the output file, in bytes. The default value if unspecified is 8192 bytes (8 kilobytes).

-c COMPRESSION

The compression algorithm to use for data blocks in the output file. The default value if unspecified is zlib. See the mtbl_info(1) manpage for the list of possible compression algorithms.