mtbl_fileset(3) automatic multiple MTBL data file merger


#include <mtbl.h>

Fileset objects:

struct mtbl_fileset *
mtbl_fileset_init(const char *

, const struct mtbl_fileset_options *

mtbl_fileset_destroy(struct mtbl_fileset **f);

mtbl_fileset_reload(struct mtbl_fileset *f);

mtbl_fileset_reload_now(struct mtbl_fileset *f);

const struct mtbl_source *
mtbl_fileset_source(struct mtbl_fileset *f);

Fileset options:

struct mtbl_fileset_options *

mtbl_fileset_options_destroy(struct mtbl_fileset_options **fopt);

        struct mtbl_fileset_options *fopt,
        mtbl_merge_func fp,
        void *clos);

        struct mtbl_fileset_options *fopt,
        uint32_t reload_interval);


The mtbl_fileset is a convenience interface for automatically maintaining a merged view of a set of MTBL data files. The merged entries may be consumed via the mtbl_source(3) and mtbl_iter(3) interfaces.

mtbl_fileset objects are initialized from a "setfile", which specifies a list of filenames of MTBL data files, one per line. Internally, an mtbl_reader object is initialized from each filename and added to an mtbl_merger object. The setfile is watched for changes and the addition or removal of filenames from the setfile will result in the corresponding addition or removal of mtbl_reader objects.

Because the MTBL format does not allow duplicate keys, the caller must provide a function which will accept a key and two conflicting values for that key and return a replacement value. This function may be called multiple times for the same key if the same key is inserted more than twice. See mtbl_merger(3) for further details about the merge function.

mtbl_fileset objects are created with the mtbl_fileset_init() function, which requires the path to a "setfile", fname, and a non-NULL fopt argument which has been configured with a merge function fp. mtbl_fileset_source() should then be called in order to consume output via the mtbl_source(3) interface.

Accesses via the mtbl_source(3) interface will implicitly check for updates to the setfile. However, it may be necessary to explicitly call the mtbl_fileset_reload() function in order to check for updates, especially if files are being removed from the setfile and the mtbl_source is infrequently accessed.

The mtbl_fileset_reload() function avoids checking for updates more frequently than every reload_interval seconds. The mtbl_fileset_reload_now() function can be called to bypass the reload_interval check.

Fileset options


See mtbl_merger(3). An mtbl_merger object is used internally for the external sort.


Specifies the interval between checks for updates to the setfile, in seconds. Defaults to 60 seconds.