[20200401]優化的困惑5.txt

lfree發表於2020-04-02

[20200401]優化的困惑5.txt

--//春節前對一個生產系統做優化,完成後使用ash_wait_chains.sql檢查,發現control file parallel write有點多。
--//當時並沒有在意,總感覺哪裡不對,感覺這套系統磁碟IO有問題,現在有空分析看看。

1.環境:
> @ ver1
PORT_STRING                    VERSION        BANNER
------------------------------ -------------- --------------------------------------------------------------------------------
x86_64/Linux 2.4.xx            11.2.0.3.0     Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production

2.問題提出:
> @ tpt/ash/dash_wait_chains event2 1=1 trunc(sysdate-2) trunc(sysdate-1)
%This     SECONDS     AAS WAIT_CHAIN
------ ---------- ------- ---------------------------------------------
  59%        2790      .0 -> control file parallel write
  21%         980      .0 -> ON CPU
  13%         640      .0 -> log file parallel write
   4%         170      .0 -> db file async I/O submit
   1%          70      .0 -> log file sync  -> log file parallel write
   1%          60      .0 -> db file sequential read
   0%          20      .0 -> LNS wait on SENDREQ
   0%          10      .0 -> os thread startup
   0%          10      .0 -> ADR block file read
9 rows selected.
--//trunc(sysdate-2) trunc(sysdate-1) 範圍在2020/3/29 2020/3/30 之間,是星期天.
--//很明顯這是一套根本不忙的系統(我已經做了許多優化),當然的時間區間也很大,不過還是可以看出伺服器不忙。
--//同時很不理解為什麼control file parallel write能達到2790秒。

3.分析:
# lsof /u01/app/oracle/oradata/xxxyyy/control01.ctl
COMMAND   PID   USER   FD   TYPE DEVICE SIZE/OFF     NODE NAME
oracle   3827 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle   3829 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle   3831 oracle  256uW  REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
oracle   3837 oracle  257u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle   3861 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle   3995 oracle  257u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle   4112 oracle  257u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  10221 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  18633 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  18688 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  18732 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  23969 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
oracle  24082 oracle  256u   REG    8,3 11812864 35061901 /u01/app/oracle/oradata/xxxyyy/control01.ctl
--//僅僅程式3831有寫。

# ps -ef | grep 383[1]
oracle    3831     1  0  2016 ?        04:13:39 ora_ckpt_xxxyyy
--//正是ckpt程式。

SYS@xxxyyy> show parameter filesystem
NAME                 TYPE   VALUE
-------------------- ------ -------
filesystemio_options string ASYNCH
--//開啟了磁碟非同步IO。

$ ls -l /proc/3831/fd  | grep control0
lrwx------ 1 oracle oinstall 64 2020-03-31 09:18:42 256 -> /u01/app/oracle/oradata/xxxyyy/control01.ctl
lrwx------ 1 oracle oinstall 64 2020-03-31 09:18:42 257 -> /u01/app/oracle/oradata/xxxyyy/control02.ctl
--//控制檔案對應檔案控制程式碼是256,257。

$ strace -f -e io_submit -Ttt  -p  3831
Process 3831 attached - interrupt to quit
09:24:52.522886 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.022249>
09:24:53.545944 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.015565>
09:24:54.561196 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.016591>
09:24:55.579054 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.015069>
09:24:56.594928 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.015453>
09:24:57.612264 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.014407>
09:24:58.627982 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.023324>
09:24:59.652000 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.032261>
09:25:00.685230 io_submit(47787382317056, 2, {{0x2b765df0c210, 0, 1, 0, 256}, {0x2b765df0c460, 0, 1, 0, 257}}) = 2 <0.081960>
Process 3831 detached
--//你可以發現每秒都呼叫一次io_submit寫入,時間間隔大約1秒1次,實際上就是寫增量檢查點,資料庫很空閒。

0.022249+0.015565+0.016591+0.015069+0.015453+0.014407+0.023324+0.032261+0.081960 = .236879
.236879/9 = .02632,平均佔.02632秒。
--//如果換算成毫秒的話,相當於26ms.這是一個相當差勁的IO,我嚴重懷疑BIOS沒有開啟寫回功能(write back),而是設定在寫通模式
--//(write through)上.

--//相當於一天呼叫 86400 /(1+.02632) = 84184次。需要84184*.02632 = 2215.72288秒,當然這是io_submit的時間,並非control file
--//parallel write.非常接近上面看到control file parallel write=2790秒。

--//再加大取樣量看看。
# strace -f -e io_submit -Ttt  -p  3831  -o/tmp/aaa
Process 3831 attached - interrupt to quit
Process 3831 detached

# cat /tmp/aaa | awk '{print $17}' | tr -d "<>"  | awk '{j++;i=i+$NF}END{print j,i,i/j}'
42 1.04516 0.0248849

--//取樣42次,0.0248849秒相當於25ms。相當慢的磁碟IO。

4.如何確定磁碟在write back還是write Through狀態呢?
--//方法一:首先想到的進入BIOS檢查,當然目前不行。
--//方法二:dmesg,沒有發現相關資訊。
--//方法三:我知道dell隨機光碟裡面有一個使用程式可以通過瀏覽器檢視硬體配置的程式。這個比較麻煩,機器已經太老了。相關資料
--//放在哪裡也不知道。
--//方法四:hdparm,看了一下man文件也沒有發現相關設定與檢查。
# hdparm 2>&1 | grep -i write
 --Istdout write identify data to stdout as ASCII hex
 -n   get/set ignore-write-errors flag (0/1)
 -W   set drive write-caching flag (0/1) (DANGEROUS)
--//看man hdparm,感覺這個命令很危險DANGEROUS,放棄。
--//方法五:想想linux還有什麼命令瞭解硬體配置呢,馬上想到dmidecode。

# dmidecode | grep -i write
        Operational Mode: Write Through
        Operational Mode: Write Through
        Operational Mode: Write Back
        Operational Mode: Write Through
        Operational Mode: Write Through
        Operational Mode: Write Back
--//很明顯了安裝人員沒有很好的設定磁碟操作模式。

# dmidecode > /tmp/aaa1
# dmidecode -t 7
# dmidecode 2.11
SMBIOS 2.7 present.

Handle 0x0700, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 1
        Operational Mode: Write Through
        Location: Internal
        Installed Size: 128 kB
        Maximum Size: 128 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Single-bit ECC
        System Type: Data
        Associativity: 8-way Set-associative

Handle 0x0701, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 2
        Operational Mode: Write Through
        Location: Internal
        Installed Size: 1024 kB
        Maximum Size: 1024 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Single-bit ECC
        System Type: Unified
        Associativity: 8-way Set-associative

Handle 0x0702, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 3
        Operational Mode: Write Back
        Location: Internal
        Installed Size: 10240 kB
        Maximum Size: 10240 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Single-bit ECC
        System Type: Unified
        Associativity: <OUT OF SPEC>

Handle 0x0703, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 1
        Operational Mode: Write Through
        Location: Internal
        Installed Size: 0 kB
        Maximum Size: 0 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Unknown
        System Type: Data
        Associativity: Unknown

Handle 0x0704, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 2
        Operational Mode: Write Through
        Location: Internal
        Installed Size: 0 kB
        Maximum Size: 0 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Unknown
        System Type: Unified
        Associativity: Unknown

Handle 0x0705, DMI type 7, 19 bytes
Cache Information
        Socket Designation: Not Specified
        Configuration: Enabled, Not Socketed, Level 3
        Operational Mode: Write Back
        Location: Internal
        Installed Size: 0 kB
        Maximum Size: 0 kB
        Supported SRAM Types:
                Unknown
        Installed SRAM Type: Unknown
        Speed: Unknown
        Error Correction Type: Unknown
        System Type: Unified
        Associativity: Unknown

# dmidecode -t 7 | egrep -i "write|Installed Size"
        Operational Mode: Write Through
        Installed Size: 128 kB
        Operational Mode: Write Through
        Installed Size: 1024 kB
        Operational Mode: Write Back
        Installed Size: 10240 kB
        Operational Mode: Write Through
        Installed Size: 0 kB
        Operational Mode: Write Through
        Installed Size: 0 kB
        Operational Mode: Write Back
        Installed Size: 0 kB

--//找了一臺相似的機器檢查發現:
# dmidecode | grep -i write
        Operational Mode: Write Back
        Operational Mode: Write Back
        Operational Mode: Write Back
        Operational Mode: Write Back
        Operational Mode: Write Back
        Operational Mode: Write Back

--//基本可以驗證我的推斷,安裝OS的人員沒有很好的設定BIOS,設定在Write Through模式導致寫入磁碟IO有點慢。
--//要麼還有一種可能就是板上可能有電池,已經沒電了,無法設定在write back模式。僅僅是我的推斷。

5.順便測試read看看:
--//session 1:
> @ spid
         SID      SERIAL# PROCESS                  SERVER    SPID       PID    P_SERIAL# C50
------------ ------------ ------------------------ --------- ------ ------- ------------ --------------------------------------------------
         843        60253 40936                    DEDICATED 4912       126           56 alter system kill session '843,60253' immediate;

> @ check
                                                                                                                                                                                                           檢查點佇列
                                                                                                                                                                                     當前時間                髒塊數量
low_rba              on_disk_rba          on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba   full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE                    CPDRT
-------------------- -------------------- ---------------- ------------------- --------------------- ---------------- ------------------- ---------------------------- ------------- ------------------- ------------
12898.27952.0        12898.31085.0        30787894340      2020-04-02 09:45:35 12898.2.16            30787875482      2020-04-02 08:53:27                        18858             1 2020-04-02 09:45:36          486

--//session 2:
# strace -x -f -e pread,io_getevents,io_submit -Ttt  -p  4912
Process 4912 attached - interrupt to quit
09:45:36.707530 pread(257, "\x15\xc2\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x04\x15\x4c\x00\x00\x00\x00\x00\x00\x00\x00\x20\x0b\x56\x37\x09\x0f"..., 16384, 16384) = 16384 <0.000024>
09:45:36.707785 pread(257, "\x15\xc2\x00\x00\x0f\x00\x00\x00\xd7\x59\x19\x00\xff\xff\x01\x04\xa8\x3c\x00\x00\x00\x47\x00\x00\x00\x00\x00\x00\x00\x00\x00\x45"..., 16384, 245760) = 16384 <0.000018>
09:45:36.707888 pread(257, "\x15\xc2\x00\x00\x11\x00\x00\x00\xd7\x59\x19\x00\xff\xff\x01\x04\xc4\x34\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xd6\x6a\xdc\x33"..., 16384, 278528) = 16384 <0.000018>
09:45:36.707985 pread(257, "\x15\xc2\x00\x00\x14\x00\x00\x00\xc8\x59\x19\x00\xff\xff\x01\x04\x2e\x77\x00\x00\x0f\x00\x00\x00\x9a\xb2\x19\x2b\x07\x00\x1c\x0a"..., 16384, 327680) = 16384 <0.000017>
09:45:36.708108 pread(257, "\x15\xc2\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x04\x5b\x9a\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\xe6\x01\x00\x00"..., 16384, 49152) = 16384 <0.000019>
Process 4912 detached

--//非同步IO讀取使用pread函式嗎,資料庫沒有使用asm原因?
--//參考連結http://blog.itpub.net/267265/viewspace-2222208/,執行如下:

> @ viewsess 'physical read total'
NAME                                     STATISTIC#        VALUE          SID
---------------------------------------- ---------- ------------ ------------
physical read total IO requests                  48          273          843
physical read total multi block requests         49            6          843
physical read total bytes                        52      6833152          843

> @ check
                                                                                                                                                                                                           檢查點佇列
                                                                                                                                                                                     當前時間                髒塊數量
low_rba              on_disk_rba          on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba   full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE                    CPDRT
-------------------- -------------------- ---------------- ------------------- --------------------- ---------------- ------------------- ---------------------------- ------------- ------------------- ------------
12898.34936.0        12898.36928.0        30787898313      2020-04-02 09:58:32 12898.2.16            30787875482      2020-04-02 08:53:27                        22831             1 2020-04-02 09:58:33          332

> @ viewsess 'physical read total'
NAME                                     STATISTIC#        VALUE          SID
---------------------------------------- ---------- ------------ ------------
physical read total IO requests                  48          278          843
physical read total multi block requests         49            6          843
physical read total bytes                        52      6915072          843

--//上下比較,可以發現physical read total IO requests增加5次(278-273=5),physical read total bytes增加 6915072-6833152=81920,正好等於16384*5= 81920.
--//你可以發現讀16384位元組 每次pread的時間很小。

總結:
--//再次提醒自己注意一些細節。資料庫上線前給仔細檢查,實際上還是我提到的分工問題,如果節點上的人做好自己的工作,
--//連結:http://blog.itpub.net/267265/viewspace-2102914/ => [20160519]淺談行業分工.txt ,這臺機器就是當年的這臺伺服器。
--//實際上如果當時我沒有再仔細看,這個問題就給劃過了。
--//還有一點要說明的是通過awr報表很容易劃過這個問題。

Top 5 Timed Foreground Events

Event                            Waits    Time(s)    Avg wait (ms)  % DB time  Wait Class
DB CPU                           265                                73.26
log file sync                    8,377         98    12             27.09      Commit
db file sequential read          6,670         15    2              4.28       User I/O
enq: KO - fast object checkpoint 151           7     47             1.95       Application
SQL*Net more data to client      176,457       3     0              0.82       Network
--//負載太輕了。不在前臺等待事件。

Background Wait Events

    ordered by wait time desc, waits desc (idle events last)
    Only events with Total Wait Time (s) >= .001 are shown
    %Timeouts: value of 0 indicates value was < .5%. Value of null is truly 0

Event                           Waits  %Time -outs  Total Wait Time (s)  Avg wait (ms)   Waits /txn      % bg time
log file parallel write         9,963            0                 112             11          1.16      37.05
control file parallel write     3,610            0                 106             29          0.42      35.23
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
db file async I/O submit        877              0                  51             59          0.10      17.08
os thread startup               37               0                   1             25          0.00      0.30
LNS wait on SENDREQ             9,935            0                   1             0           1.16      0.17
--//注意看 Avg wait (ms) ,只能講自己功力還是不夠,沒有仔細看這些細節,主要精力放在前臺事件的優化上了,忽略後後臺事件。
--//磁碟IO存在問題。

--//附上測試指令碼:
$ cat check.sql
column "full checkpoint_rba" format a21
column low_rba format a20
column low_rba16 format a20
column on_disk_rba format a20
column on_disk_rba16 format a20
column rtckp_rba format a20
column diff_date format 9999999.99
rem column CPOSD_ono_disk_rba_scn format 99999999999999999999999999999999
column cpdrt heading "檢查點佇列|髒塊數量|CPDRT"
column cpodt_on_disk_rba heading "檢查點佇列|on disk rba|時間戳|CPODT"
column cpods heading "檢查點佇列|on disk rba scn|CPODS"
column cphbt heading "檢查點心跳|CPHBT"
column current_sysdate heading "當前時間|SYSDATE"
set num 12

SELECT b.cplrba_seq || '.' || b.cplrba_bno || '.' || b.cplrba_bof "low_rba"
      ,b.cpodr_seq || '.' || b.cpodr_bno || '.' || b.cpodr_bof "on_disk_rba"
      ,b.CPODS "on_disk_rba_scn(CPODS)"
      ,TO_DATE (b.CPODT, 'MM-DD-YYYY HH24:MI:SS') "on_disk_rba_time(CPODT)"
      ,a.rtckp_rba_seq || '.' || a.rtckp_rba_bno || '.' || a.rtckp_rba_bof
          "full checkpoint_rba"
      ,a.rtckp_scn "full_checkpoint(rtckp_scn)"
      ,TO_DATE (a.rtckp_tim, 'MM-DD-YYYY HH24:MI:SS')
          "full_checkpoint_time_rtckp_tim"
      ,b.CPODS - a.rtckp_scn "diff_scn(on_disk_rdb-ch_scn)"
      ,a.rtcln "current_group"
      ,sysdate current_sysdate
          ,CPDRT
  FROM x$kccrt a, x$kcccp b
 WHERE a.rtnum = b.cptno AND A.INST_ID = b.inst_id;

$ cat viewsess.sql
set verify off
column name format a70
SELECT b.NAME, a.statistic#, a.VALUE,a.sid
  FROM v$mystat a, v$statname b
 WHERE lower(b.NAME) like lower('%&1%') AND a.statistic# = b.statistic#
 and a.value>0;

來自 “ ITPUB部落格 ” ,連結:http://blog.itpub.net/267265/viewspace-2684072/,如需轉載,請註明出處,否則將追究法律責任。

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