函数 page_dir_get_n_heap

#define    PAGE_N_HEAP     4    /* number of records in the heap,
                bit 15=flag: new-style compact page format */

/*************************************************************//**
Gets the number of records in the heap.
@return    number of user records */
UNIV_INLINE
ulint
page_dir_get_n_heap(
/*================*/
    const page_t*    page)    /*!< in: index page */
{
    return(page_header_get_field(page, PAGE_N_HEAP) & 0x7fff);
}

/*************************************************************//**
Reads the given header field. */
UNIV_INLINE
ulint
page_header_get_field(
/*==================*/
    const page_t*    page,    /*!< in: page */
    ulint        field)    /*!< in: PAGE_LEVEL, ... */
{
    ut_ad(page);
    ut_ad(field <= PAGE_INDEX_ID);

    return(mach_read_from_2(page + PAGE_HEADER + field));
}

#define    PAGE_HEADER    FSEG_PAGE_DATA    /* index page header starts at this offset */

#define FSEG_PAGE_DATA        FIL_PAGE_DATA

#define FIL_PAGE_DATA        38