结构体dict_index_t;

/** InnoDB B-tree index */
typedef struct dict_index_struct dict_index_t;

/** Data structure for an index.  Most fields will be
initialized to 0, NULL or FALSE in dict_mem_index_create(). */
struct dict_index_struct{
    index_id_t    id;    /*!< id of the index */
    mem_heap_t*    heap;    /*!< memory heap */
    const char*    name;    /*!< index name */
    const char*    table_name;/*!< table name */
    dict_table_t*    table;    /*!< back pointer to table */ //详见
#ifndef UNIV_HOTBACKUP
    unsigned    space:32;
                /*!< space where the index tree is placed */
    unsigned    page:32;/*!< index tree root page number */
#endif /* !UNIV_HOTBACKUP */
    unsigned    type:DICT_IT_BITS;
                /*!< index type (DICT_CLUSTERED, DICT_UNIQUE,
                DICT_UNIVERSAL, DICT_IBUF, DICT_CORRUPT) */
#define MAX_KEY_LENGTH_BITS 12
    unsigned    trx_id_offset:MAX_KEY_LENGTH_BITS;
                /*!< position of the trx id column
                in a clustered index record, if the fields
                before it are known to be of a fixed size,
                0 otherwise */
#if (1<<MAX_KEY_LENGTH_BITS) < MAX_KEY_LENGTH
# error (1<<MAX_KEY_LENGTH_BITS) < MAX_KEY_LENGTH
#endif
    unsigned    n_user_defined_cols:10;
                /*!< number of columns the user defined to
                be in the index: in the internal
                representation we add more columns */
    unsigned    n_uniq:10;/*!< number of fields from the beginning
                which are enough to determine an index
                entry uniquely */
    unsigned    n_def:10;/*!< number of fields defined so far */
    unsigned    n_fields:10;/*!< number of fields in the index */
    unsigned    n_nullable:10;/*!< number of nullable fields */
    unsigned    cached:1;/*!< TRUE if the index object is in the
                dictionary cache */
    unsigned    to_be_dropped:1;
                /*!< TRUE if this index is marked to be
                dropped in ha_innobase::prepare_drop_index(),
                otherwise FALSE. Protected by
                dict_sys->mutex, dict_operation_lock and
                index->lock.*/
    dict_field_t*    fields;    /*!< array of field descriptions */
#ifndef UNIV_HOTBACKUP
    UT_LIST_NODE_T(dict_index_t)
            indexes;/*!< list of indexes of the table */
    btr_search_t*    search_info; /*!< info used in optimistic searches */
    /*----------------------*/
    /** Statistics for query optimization */
    /* @{ */
    ib_int64_t*    stat_n_diff_key_vals;
                /*!< approximate number of different
                key values for this index, for each
                n-column prefix where n <=
                dict_get_n_unique(index); we
                periodically calculate new
                estimates */
    ib_int64_t*    stat_n_non_null_key_vals;
                /* approximate number of non-null key values
                for this index, for each column where
                n < dict_get_n_unique(index); This
                is used when innodb_stats_method is
                "nulls_ignored". */
    ulint        stat_index_size;
                /*!< approximate index size in
                database pages */
    ulint        stat_n_leaf_pages;
                /*!< approximate number of leaf pages in the
                index tree */
    /* @} */
    rw_lock_t    lock;    /*!< read-write lock protecting the
                upper levels of the index tree */
    trx_id_t    trx_id; /*!< id of the transaction that created this
                index, or 0 if the index existed
                when InnoDB was started up */
#endif /* !UNIV_HOTBACKUP */
#ifdef UNIV_BLOB_DEBUG
    mutex_t        blobs_mutex;
                /*!< mutex protecting blobs */
    void*        blobs;    /*!< map of (page_no,heap_no,field_no)
                to first_blob_page_no; protected by
                blobs_mutex; @see btr_blob_dbg_t */
#endif /* UNIV_BLOB_DEBUG */
#ifdef UNIV_DEBUG
    ulint        magic_n;/*!< magic number */
/** Value of dict_index_struct::magic_n */
# define DICT_INDEX_MAGIC_N    76789786
#endif
};