NAME

       mtbl_merger - merge multiple MTBL data sources into a single output

SYNOPSIS

       #include <mtbl.h>

       Merger objects:

       struct mtbl_merger *
       mtbl_merger_init(const struct mtbl_merger_options *mopt);

       void
       mtbl_merger_destroy(struct mtbl_merger **m);

       void
       mtbl_merger_add_source(struct mtbl_merger *m, const struct mtbl_source *s);

       const struct mtbl_source *
       mtbl_merger_source(struct mtbl_merger *m);

       Merger options:

       struct mtbl_merger_options *
       mtbl_merger_options_init(void);

       void
       mtbl_merger_options_destroy(struct mtbl_merger_options **mopt);

       void
       mtbl_merger_options_set_merge_func(
               struct mtbl_merger_options *mopt,
               mtbl_merge_func fp,
               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);

DESCRIPTION

       Multiple MTBL data sources may be merged together using the mtbl_merger interface, which
       reads key-value entries from one or more sources and provides these entries in sorted
       order. The sorted entries may be consumed via the mtbl_source(3) and mtbl_iter(3)
       interfaces.

       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 more than two
       sources are being merged.

       mtbl_merger objects are created with the mtbl_merger_init() function, which requires a
       non-NULL mopt argument which has been configured with a merge function fp.

       One or more mtbl_reader objects must be provided as input to the mtbl_merger object by
       calling mtbl_merger_add_source(). After the desired sources have been configured,
       mtbl_merger_source() should be called in order to consume the merged output via the
       mtbl_source(3) interface.

   Merger options
       merge_func
           This option specifies a merge function callback, consisting of a function pointer fp
           and a pointer to user data clos which will be passed as the first argument to fp. The
           merge function callback will be used during iteration over the mtbl_merger object to
           merge entries with duplicate keys in the input sources.

           The remaining arguments to the merge function are:

           key — pointer to the key for which there exist duplicate values.

           len_key — length of the key.

           val0 — pointer to the first value.

           len_val_0 — length of the first value.

           val1 — pointer to the second value.

           len_val_1 — length of the second value.

           merged_val — pointer to where the callee should place its merged value.

           len_merged_val — pointer to where the callee should place the length of its merged
           value.

           merged_val must be allocated with the system allocator, and the mtbl_merger interface
           takes responsibility for free()ing the value once it is no longer needed.

           The callee may provide an empty value as the merged value, in which case merged_val
           must still contain an allocated, non-NULL value and len_merged_val must contain the
           value 0.

           The callee may indicate an error by returning NULL in the merged_val argument, which
           will abort iteration over the mtbl_merger object.

RETURN VALUE

       If the merge function callback is unable to provide a merged value (that is, it fails to
       return a non-NULL value in its merged_val argument), the merge process will be aborted,
       and any iterators over the mtbl_merger object (via the mtbl_source(3) interface) will
       return mtbl_res_failure.

                                            01/31/2014                             MTBL_MERGER(3)