MySQL 8.0 information_schema系統庫的改進

時間 2019-12-13

標籤 mysql 8.0 information schema 系統改進欄目 MySQL 简体版

原文原文鏈接

目錄mysql

information_schema有何用？

經過I_S獲取mysql的一些元數據信息
獲取表的數據文件、索引文件的大小、碎片狀況、錶行數、自增列增加狀況等
獲取正在運行的事務有那些，是否有阻塞等
獲取當前mysql的鏈接processlist等等

mysql8.0 以前的查詢方式

會在查詢information_schema 某個表時建立臨時表sql

來自文件的元數據，掃描文件系統獲取FRM文件的表定義
存儲引擎的詳細信息，例如動態表統計信息
來自MySQL服務器中全局數據結構的數據

在表的數量不少時，每次查詢I_S會從文件系統中讀取每一個單獨的FRM文件，使用更多的CPU週期來打開表並準備相關的內存數據結構數據庫

mysql8.0 開始的查詢方式

引入了基於InnoDB的本地數據字典表
表中不在有FRM表定義文件
全部數據庫表的元數據都存儲在事務數據字典表中
I_S中表被設計爲數據字典表上的VIEW（有些仍是臨時表0_0）

消除了如下成本
查詢INFORMATION_SCHEMA時建立的臨時表
掃描文件系統目錄以查找FRM文件bash

改進
利用MySQL優化器的所有功能，使用數據字典表上的索引來更好的查詢服務器

mysql5.7中表文件
ll test*
Jul 10 10:52 testse.frm
Jul 10 10:52 testse.ibd數據結構

mysql8.0中表文件併發

ll test*
Jul 10 10:25 testse.ibddom

mysql5.7 和mysql8.0 I_S 中tables 表的存在方式ide

mysql5.7.22 
show create table information_schema.tables\G
*************************** 1. row ***************************
       Table: TABLES
Create Table: CREATE TEMPORARY TABLE `TABLES` (
  `TABLE_CATALOG` varchar(512) NOT NULL DEFAULT '',
  `TABLE_SCHEMA` varchar(64) NOT NULL DEFAULT '',
  `TABLE_NAME` varchar(64) NOT NULL DEFAULT '',
  `TABLE_TYPE` varchar(64) NOT NULL DEFAULT '',
  `ENGINE` varchar(64) DEFAULT NULL,

mysql8.0.15
  show create table information_schema.tables\G
*************************** 1. row ***************************
                View: TABLES
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`mysql.infoschema`@`localhost` SQL SECURITY DEFINER VIEW `

mysql5.7 中I_S中tables表是以臨時表的形式存在的（查詢該表就會建立臨時表，建立的臨時表過多，可能會致使mysql佔用的內存暴漲，出現OOM）
mysql8.0 中I_S中tables表以視圖的形式存在（查詢該視圖，不會建立臨時表，會使用到視圖中表的索引）

mysql5.7中獲取表大小狀況sqlserver

SELECT   table_name,   CONCAT(FORMAT(data_length / 1024 / 1024, 2),   'M') AS dbdata_size,   CONCAT(FORMAT(index_length / 1024 / 1024, 2),   'M') AS dbindex_size,   CONCAT(     FORMAT((data_length + index_length) / 1024 / 1024 / 1024,2),   'G') AS `db_size(G)`,   AVG_ROW_LENGTH,   table_rows,   update_time FROM   information_schema.tables WHERE table_schema = 'test'   AND table_name = 'testse';
+------------+-------------+--------------+------------+----------------+------------+---------------------+
| table_name | dbdata_size | dbindex_size | db_size(G) | AVG_ROW_LENGTH | table_rows | update_time         |
+------------+-------------+--------------+------------+----------------+------------+---------------------+
| testse     | 0.02M       | 0.02M        | 0.00G      |            862 |         19 | 2019-07-10 10:52:02 |
+------------+-------------+--------------+------------+----------------+------------+---------------------+


執行計劃中出現了where，未用到索引（存儲引擎檢索數據後，server層進行過濾）
desc SELECT   table_name,   CONCAT(FORMAT(data_length / 1024 / 1024, 2),   'M') AS dbdata_size,   CONCAT(FORMAT(index_length / 1024 / 1024, 2),   'M') AS dbindex_size,   CONCAT(     FORMAT(data_length + index_length / 1024 / 1024 / 1024,     2   ),   'G') AS `db_size(G)`,   AVG_ROW_LENGTH,   table_rows,   update_time FROM   information_schema.tables WHERE table_schema = 'test'   AND table_name = 'testse';
+----+-------------+--------+------------+------+---------------+-------------------------+---------+------+------+----------+---------------------------------------------------+
| id | select_type | table  | partitions | type | possible_keys | key                     | key_len | ref  | rows | filtered | Extra                                             |
+----+-------------+--------+------------+------+---------------+-------------------------+---------+------+------+----------+---------------------------------------------------+
|  1 | SIMPLE      | tables | NULL       | ALL  | NULL          | TABLE_SCHEMA,TABLE_NAME | NULL    | NULL | NULL |     NULL | Using where; Open_full_table; Scanned 0 databases |
+----+-------------+--------+------------+------+---------------+-------------------------+---------+------+------+----------+---------------------------------------------------+

mysql8.0中獲取表大小狀況

SELECT   table_name,   CONCAT(FORMAT(data_length / 1024 / 1024, 2),   'M') AS dbdata_size,   CONCAT(FORMAT(index_length / 1024 / 1024, 2),   'M') AS dbindex_size,   CONCAT(     FORMAT((data_length + index_length) / 1024 / 1024 / 1024,2),   'G') AS `db_size(G)`,   AVG_ROW_LENGTH,   table_rows,   update_time FROM   information_schema.tables WHERE table_schema = 'test'   AND table_name = 'testse';
+------------+-------------+--------------+------------+----------------+------------+---------------------+
| TABLE_NAME | dbdata_size | dbindex_size | db_size(G) | AVG_ROW_LENGTH | TABLE_ROWS | UPDATE_TIME         |
+------------+-------------+--------------+------------+----------------+------------+---------------------+
| testse     | 0.02M       | 0.02M        | 0.00G      |            862 |         19 | 2019-07-10 10:25:16 |
+------------+-------------+--------------+------------+----------------+------------+---------------------+



能使用到數據字典表的索引
desc SELECT   table_name,   CONCAT(FORMAT(data_length / 1024 / 1024, 2),   'M') AS dbdata_size,   CONCAT(FORMAT(index_length / 1024 / 1024, 2),   'M') AS dbindex_size,   CONCAT(     FORMAT((data_length + index_length) / 1024 / 1024 / 1024,2),   'G') AS `db_size(G)`,   AVG_ROW_LENGTH,   table_rows,   update_time FROM   information_schema.tables WHERE table_schema = 'test'   AND table_name = 'testse';
+----+-------------+-------+------------+--------+--------------------+------------+---------+-------------------------+------+----------+-------------+
| id | select_type | table | partitions | type   | possible_keys      | key        | key_len | ref                     | rows | filtered | Extra       |
+----+-------------+-------+------------+--------+--------------------+------------+---------+-------------------------+------+----------+-------------+
|  1 | SIMPLE      | cat   | NULL       | index  | PRIMARY            | name       | 194     | NULL                    |    1 |   100.00 | Using index |
|  1 | SIMPLE      | sch   | NULL       | eq_ref | PRIMARY,catalog_id | catalog_id | 202     | mysql.cat.id,const      |    1 |   100.00 | Using index |
|  1 | SIMPLE      | tbl   | NULL       | eq_ref | schema_id          | schema_id  | 202     | mysql.sch.id,const      |    1 |   100.00 | Using where |
|  1 | SIMPLE      | stat  | NULL       | const  | PRIMARY            | PRIMARY    | 388     | const,const             |    1 |   100.00 | NULL        |
|  1 | SIMPLE      | ts    | NULL       | eq_ref | PRIMARY            | PRIMARY    | 8       | mysql.tbl.tablespace_id |    1 |   100.00 | NULL        |
|  1 | SIMPLE      | col   | NULL       | eq_ref | PRIMARY            | PRIMARY    | 8       | mysql.tbl.collation_id  |    1 |   100.00 | Using index |
+----+-------------+-------+------------+--------+--------------------+------------+---------+-------------------------+------+----------+-------------+

測試5.7和8.0不一樣版本訪問I_S庫的性能

機器

cat /etc/redhat-release | xargs echo '版本 ' && dmidecode -s system-product-name | xargs echo '是否虛擬化 ' && cat /proc/cpuinfo |grep "processor"|wc -l | xargs echo 'cpu核數 '
版本  CentOS Linux release 7.5.1804 (Core)
是否虛擬化  KVM
cpu核數  4

一、分別在mysql5.7和mysql8.0 中建立5個庫，每一個庫中30個表（共1500個表），每一個表記錄數爲10000

user=admin
passwd=admin
port=57222
host=127.0.0.1

#建立5個庫,分別在每一個庫中建立30個表
for i in {1..5};do

mysql -u$user -p$passwd -P$port -h$host<<EOF
  create database if not exists test_${i};

EOF

sysbench /usr/local/share/sysbench/oltp_read_write.lua --mysql_storage_engine=innodb  --table-size=10000 --tables=30 --mysql-db=test_${i} --mysql-user=$user --mysql-password=$passwd --mysql-port=$port  --mysql-host=$host --threads=8 --time=10 --report-interval=1 --events=0 --db-driver=mysql prepare
done;

二、自定義訪問I_S.tables表的sysbench腳本
cat tests/mytest.lua

require("oltp_common")


function thread_init(thread_id)
 drv=sysbench.sql.driver()
 con=drv:connect()
end


local function get_rand_db()
   return sysbench.rand.uniform(1, 5)
end



function event(thread_id)
local vid1
local dbprefix


vid1=get_rand_db()
dbprefix = "test_"

-- 生成5個db中的隨機一個db,如 test_1 ,test_5
-- vid2=string.format("'%s%s'",test_,vid1)
vid2="'" .. dbprefix .. vid1 .. "'"

con:query("SELECT   table_name,   CONCAT(FORMAT(data_length / 1024 / 1024, 2),   'M') AS dbdata_size,   CONCAT(FORMAT(index_length / 1024 / 1024, 2),   'M') AS dbindex_size,   CONCAT(     FORMAT((data_length + index_length) / 1024 / 1024 / 1024,2),   'G') AS `db_size(G)`,   AVG_ROW_LENGTH,   table_rows,   update_time FROM   information_schema.tables WHERE table_schema =" .. vid2)

end

function thread_done()
 con:disconnect()
end

三、腳本經過sysbench測試訪問I_S.tables的qps
cat test_I_S_access.sh

user=admin
passwd=admin
host=127.0.0.1
#輸入mysql端口參數
port=$1
# port=8015
#輸入sysbench測試時間參數多少秒
run_time=$2

function get_create_tmp_tables(){
mysql -u$user -p$passwd -P$port -h$host<<EOF
select @@version as 'mysql version';

show global  status like '%tmp_table%';
EOF
} 2>/dev/null

function begin_test(){
  cd /usr/local/share/sysbench
   sysbench ./tests/mytest.lua --mysql-db=test_1  --mysql-host=$host --mysql-port=$port --mysql-user=$user --mysql-password=$passwd  --threads=40  --report-interval=10 --rand-type=uniform --time=$run_time    run
}


service mysqld${port} restart
get_create_tmp_tables
begin_test
get_create_tmp_tables

四、mysql5.7和mysql8.0 主要配置

mysql5.7.22

5.7.22-log
innodb_buffer_pool_size 128M
innodb_log_buffer_size  64M
innodb_log_file_size    48M
binlog_format   ROW
innodb_flush_log_at_trx_commit  1
sync_binlog     1

mysql8.0.15

8.0.15
innodb_buffer_pool_size 128M
innodb_log_buffer_size  64M
innodb_log_file_size    48M
binlog_format   ROW
innodb_flush_log_at_trx_commit  1
sync_binlog     1

五、mysql5.7開啓測試
bash test_I_S_acess.sh 57222 60

Shutting down MySQL.. SUCCESS!
Starting MySQL.. SUCCESS!
mysql version
5.7.22-log
Variable_name   Value
Created_tmp_tables      1
sysbench 1.1.0 (using bundled LuaJIT 2.1.0-beta3)

Running the test with following options:
Number of threads: 40
Report intermediate results every 10 second(s)
Initializing random number generator from current time


Initializing worker threads...

Threads started!

[ 10s ] thds: 40 tps: 4765.73 qps: 4765.73 (r/w/o: 4765.73/0.00/0.00) lat (ms,95%): 18.95 err/s: 0.00 reconn/s:                                                                                                              0.00
[ 20s ] thds: 40 tps: 5409.00 qps: 5409.00 (r/w/o: 5409.00/0.00/0.00) lat (ms,95%): 17.95 err/s: 0.00 reconn/s:                                                                                                              0.00
[ 30s ] thds: 40 tps: 5154.45 qps: 5154.45 (r/w/o: 5154.45/0.00/0.00) lat (ms,95%): 18.61 err/s: 0.00 reconn/s:                                                                                                              0.00
[ 40s ] thds: 40 tps: 5383.50 qps: 5383.50 (r/w/o: 5383.50/0.00/0.00) lat (ms,95%): 17.63 err/s: 0.00 reconn/s:                                                                                                              0.00
[ 50s ] thds: 40 tps: 5456.11 qps: 5456.11 (r/w/o: 5456.11/0.00/0.00) lat (ms,95%): 17.63 err/s: 0.00 reconn/s:                                                                                                              0.00
[ 60s ] thds: 40 tps: 5458.66 qps: 5458.66 (r/w/o: 5458.66/0.00/0.00) lat (ms,95%): 17.63 err/s: 0.00 reconn/s:                                                                                                              0.00
SQL statistics:
    queries performed:
        read:                            316322
        write:                           0
        other:                           0
        total:                           316322
    transactions:                        316322 (5270.99 per sec.)
    queries:                             316322 (5270.99 per sec.)
    ignored errors:                      0      (0.00 per sec.)
    reconnects:                          0      (0.00 per sec.)

Throughput:
    events/s (eps):                      5270.9892
    time elapsed:                        60.0119s
    total number of events:              316322

Latency (ms):
         min:                                    0.42
         avg:                                    7.59
         max:                                  858.18
         95th percentile:                       17.95
         sum:                              2399738.58

Threads fairness:
    events (avg/stddev):           7908.0500/53.41
    execution time (avg/stddev):   59.9935/0.00

mysql version
5.7.22-log
Variable_name   Value
Created_tmp_tables      316327

cpu使用率接近100%

mysql5.7.22 40個併發線程壓力測試60秒，訪問I_S.tables 平均qps爲5k，並建立了31w個臨時表!

六、mysql8.0開啓測試

Shutting down MySQL.. SUCCESS!
Starting MySQL.... SUCCESS!
mysql version
8.0.15
Variable_name   Value
Created_tmp_tables      1
sysbench 1.1.0 (using bundled LuaJIT 2.1.0-beta3)

Running the test with following options:
Number of threads: 40
Report intermediate results every 10 second(s)
Initializing random number generator from current time


Initializing worker threads...

Threads started!

[ 10s ] thds: 40 tps: 1283.76 qps: 1283.76 (r/w/o: 1283.76/0.00/0.00) lat (ms,95%): 41.10 err/s: 0.00 reconn/s: 0.00
[ 20s ] thds: 40 tps: 1286.43 qps: 1286.43 (r/w/o: 1286.43/0.00/0.00) lat (ms,95%): 39.65 err/s: 0.00 reconn/s: 0.00
[ 30s ] thds: 40 tps: 1333.00 qps: 1333.00 (r/w/o: 1333.00/0.00/0.00) lat (ms,95%): 37.56 err/s: 0.00 reconn/s: 0.00
[ 40s ] thds: 40 tps: 1280.79 qps: 1280.79 (r/w/o: 1280.79/0.00/0.00) lat (ms,95%): 40.37 err/s: 0.00 reconn/s: 0.00
[ 50s ] thds: 40 tps: 1313.57 qps: 1313.57 (r/w/o: 1313.57/0.00/0.00) lat (ms,95%): 38.94 err/s: 0.00 reconn/s: 0.00
[ 60s ] thds: 40 tps: 1222.95 qps: 1222.95 (r/w/o: 1222.95/0.00/0.00) lat (ms,95%): 42.61 err/s: 0.00 reconn/s: 0.00
SQL statistics:
    queries performed:
        read:                            77248
        write:                           0
        other:                           0
        total:                           77248
    transactions:                        77248  (1286.95 per sec.)
    queries:                             77248  (1286.95 per sec.)
    ignored errors:                      0      (0.00 per sec.)
    reconnects:                          0      (0.00 per sec.)

Throughput:
    events/s (eps):                      1286.9486
    time elapsed:                        60.0242s
    total number of events:              77248

Latency (ms):
         min:                                    1.88
         avg:                                   31.08
         max:                                  692.98
         95th percentile:                       40.37
         sum:                              2400505.33

Threads fairness:
    events (avg/stddev):           1931.2000/51.17
    execution time (avg/stddev):   60.0126/0.00

mysql version
8.0.15
Variable_name   Value
Created_tmp_tables      2

cpu使用率接近100%

mysql8.0.15 40個併發線程，壓力測試60秒，訪問I_S.tables 平均qps爲1.2k，並建立了1個臨時表!

結論

mysql8.0開始查詢I_S中表不會再從文件系統(FRM, TRG，OPT文件)和myisam、innodb系統表讀取元數據信息（8.0開始元數據信息統一存放在數據字典表中）
mysql8.0 訪問I_S.tables不會建立臨時表，這減小了內存暴漲的可能，但訪問I_S.tables的qps大約是mysql5.7.22的1/5，訪問速度沒有mysql5.7.22的快
mysql8.0 訪問I_S.tables 用戶空間cpu消耗沒有mysql5.7的高（沒有建立臨時表的緣故吧），但系統空間cpu消耗高於mysql5.7！

參考
MySQL 8.0: Improvements to Information_schema