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DNSTABLE_MERGE_FUNC(3)                                  DNSTABLE_MERGE_FUNC(3)

NAME
       dnstable_merge_func - libmtbl merge function for dnstable key-value
       entries

SYNOPSIS
       #include <dnstable.h>

       void
       dnstable_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
       This is the libmtbl merging function for dnstable key-value entries.
       dnstable is built on libmtbl, and libmtbl requires a "merge function"
       to resolve conflicting values between identical keys. The symbol
       dnstable_merge_func can be provided to libmtbl functions requiring a
       merge function when dealing with dnstable key-value data.

       There are four dnstable MTBL key-value entry types. dnstable_merge_func
       handles them in the following manner:

       ENTRY_TYPE_RRSET_NAME_FWD and ENTRY_TYPE_RDATA_NAME_REV entries have no
       associated value (that is, the values for these types is zero length).
       A zero-length byte array is provided as the merged value.

       ENTRY_TYPE_RRSET and ENTRY_TYPE_RDATA entries have an identical
       encoding format. These types encode a triplet of varint-encoded
       integers representing the time_first, time_last, and count value
       fields. A new triplet of varint-encoded integers is generated as the
       merged value as follows:

       o   The earliest (that is, smallest) of the two time_first values is
           taken as the merged time_first value.

       o   The latest (that is, largest) of the two time_last values is taken
           as the merged time_last value.

       o   The two count values are added together.

SEE ALSO
       dnstable-encoding(5), mtbl_merger(3)

                                  11/10/2015            DNSTABLE_MERGE_FUNC(3)