MySQL中Innodb表Data free怎么计算

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大概是空闲extent的大小。

ST_FIELD_INFO tables_fields_info[]={...  {"DATA_FREE", MY_INT64_NUM_DECIMAL_DIGITS, MYSQL_TYPE_LONGLONG, 0,   (MY_I_S_MAYBE_NULL | MY_I_S_UNSIGNED), "Data_free", OPEN_FULL_TABLE},...}tables_fields_info[12]就是Data_free

ST_SCHEMA_TABLE schema_tables[]={... {"TABLES", tables_fields_info, create_schema_table,    get_all_tables, make_old_format, get_schema_tables_record, 1, 2, 0,   OPTIMIZE_I_S_TABLE},...}填充方式get_schema_tables_record函数

其中有一句table->field[12]->store((longlong) file->stats.delete_length, TRUE);实际就是 file->stats.delete_length

其中 file->stats.delete_length调用进行取值

ha_innobase::info_low其中包含avail_space = fsp_get_available_space_in_free_extents(ib_table->space);stats.delete_length = avail_space * 1024;

uintmax_tfsp_get_available_space_in_free_extents(    const fil_space_t*  space){    ut_ad(space->n_pending_ops > 0);    ulint   size_in_header = space->size_in_header;//总的页面大小    if (size_in_header < FSP_EXTENT_SIZE) { //碎片页 直接返回0        return(0);      /* TODO: count free frag pages and                    return a value based on that */    }    /* Below we play safe when counting free extents above the free limit:    some of them will contain extent descriptor pages, and therefore    will not be free extents */    ut_ad(size_in_header >= space->free_limit);    ulint   n_free_up =        (size_in_header - space->free_limit) / FSP_EXTENT_SIZE; //(总的页面大小-已经初始化大小)/EXTENT SIZE    page_size_t page_size(space->flags);    if (n_free_up > 0) {        n_free_up--;        n_free_up -= n_free_up / (page_size.physical()                      / FSP_EXTENT_SIZE); //减去extent管理块?    }    /* We reserve 1 extent + 0.5 % of the space size to undo logs    and 1 extent + 0.5 % to cleaning operations; NOTE: this source    code is duplicated in the function above! */    ulint   reserve = 2 + ((size_in_header / FSP_EXTENT_SIZE) * 2) / 200;    ulint   n_free = space->free_len + n_free_up;    if (reserve > n_free) {        return(0);    }    return(static_cast(n_free - reserve)           * FSP_EXTENT_SIZE * (page_size.physical() / 1024));}

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