DragonFly On-Line Manual Pages

Search: Section:  

MTBL_READER(3)                                                  MTBL_READER(3)


NAME

       mtbl_reader - read an MTBL file


SYNOPSIS

       #include <mtbl.h>

       Reader objects:

       struct mtbl_reader *
       mtbl_reader_init(const char *fname, const struct mtbl_reader_options *ropt);

       struct mtbl_reader *
       mtbl_reader_init_fd(int fd, const struct mtbl_reader_options *ropt);

       void
       mtbl_reader_destroy(struct mtbl_reader **r);

       const struct mtbl_source *
       mtbl_reader_source(struct mtbl_reader *r);

       const struct mtbl_metadata *
       mtbl_reader_metadata(struct mtbl_reader *r);

       Reader options:

       struct mtbl_reader_options *
       mtbl_reader_options_init(void);

       void
       mtbl_reader_options_destroy(struct mtbl_reader_options **ropt);

       void
       mtbl_reader_options_set_verify_checksums(
               struct mtbl_reader_options *ropt,
               bool verify_checksums);

       void
       mtbl_reader_options_set_madvise_random(
               struct mtbl_reader_options *ropt,
               bool madvise_random);


DESCRIPTION

       MTBL files are accessed by creating an mtbl_reader object, calling
       mtbl_reader_source() to obtain an mtbl_source handle, and using the
       mtbl_source(3) interface to read entries.

       mtbl_reader objects may be created by calling mtbl_reader_init() with
       an fname argument specifying the filename to be opened, or
       mtbl_reader_init_fd() may be called with an fd argument specifying an
       open, readable file descriptor. Since MTBL files are immutable, the
       same MTBL file may be opened and read from concurrently by independent
       threads or processes.

       If the ropt parameter to mtbl_reader_init() or mtbl_reader_init_fd() is
       non-NULL, the parameters specified in the mtbl_reader_options object
       will be configured into the mtbl_reader object.

       File-level metadata may be accessed using the mtbl_metadata(3)
       interface, using the object returned by mtbl_reader_metadata(). Note
       that the metadata object is valid only as long as the reader object
       exists.

   Reader options
       verify_checksums

           Specifies whether or not the CRC32C checksum on each data block
           should be verified or not. If verify_checksums is enabled, a
           checksum mismatch will cause a runtime error. Note that the
           checksum on the index block is always verified, since the overhead
           of doing this once when the reader object is instantiated is
           minimal. The default is to not verify data block checksums.

       madvise_random

           Specifies whether the kernel should be advised if the data access
           patterns are expected to be random or not. This may hurt some
           workloads but help others. The default is to not set this advisory
           information.

           This option can be explicitly overridden by setting the environment
           variable MTBL_READER_MADVISE_RANDOM to the string "0" (force
           disable) or "1" (force enable).

           This option only has any effect on systems that have the
           posix_madvise or madvise system calls.


RETURN VALUE

       mtbl_reader_init() and mtbl_reader_init_fd() return NULL on failure,
       and non-NULL on success.

                                  02/03/2015                    MTBL_READER(3)

Search: Section: