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MTBL_FILESET(3)   MTBL_FILESET(3)

mtbl_fileset - automatic multiple MTBL data file merger

#include <mtbl.h>
Fileset objects:
struct mtbl_fileset *
mtbl_fileset_init(const char *fname, const struct mtbl_fileset_options *fopt);
void
mtbl_fileset_destroy(struct mtbl_fileset **f);
void
mtbl_fileset_reload(struct mtbl_fileset *f);
void
mtbl_fileset_reload_now(struct mtbl_fileset *f);
const struct mtbl_source *
mtbl_fileset_source(struct mtbl_fileset *f);
void
mtbl_fileset_partition(struct mtbl_fileset *f,
                mtbl_filename_filter_func cb,
                void *clos,
                struct mtbl_merger **m1,
                struct mtbl_merger **m2);
Fileset options:
struct mtbl_fileset_options *
mtbl_fileset_options_init(void);
void
mtbl_fileset_options_destroy(struct mtbl_fileset_options **fopt);
void
mtbl_fileset_options_set_merge_func(
        struct mtbl_fileset_options *fopt,
        mtbl_merge_func fp,
        void *clos);
void
mtbl_fileset_options_set_reload_interval(
        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. If reload_interval is set to MTBL_FILESET_RELOAD_INTERVAL_NEVER, then mtbl_fileset_reload() function will only load the fileset once. The mtbl_fileset_reload_now() function can be called to bypass the reload_interval check.
The mtbl_fileset_partition() function yields two struct mtbl_merger objects that are split based on the output of a callback. The caller is responsible for calling mtbl_merger_destroy() on each of these mergers. Calls to mtbl_source_*() on the fileset’s source object, and calls to mtbl_fileset_reload() and mtbl_fileset_reload_now() may leave these mergers in an inconsistent state.

merge_func
 
See mtbl_merger(3). An mtbl_merger object is used internally for the external sort.
 
reload_interval
 
Specifies the interval between checks for updates to the setfile, in seconds. Defaults to 60 seconds. MTBL_FILESET_RELOAD_INTERVAL_NEVER is a special value that indicates to never reload the fileset.
05/22/2018  

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