[20200401]优化的困惑5.txt--//春节前对一个生产系统做优化，完成后使用ash_wait_chains.sql检查，发现control file parallel write有点多。--//当时并没有在意，总感觉哪里
![[20200401]优化的困惑5.txt](/upload/202205/01/ws3pb1tb314.jpg)
[20200401]优化的困惑5.txt
--//春节前对一个生产系统做优化，完成后使用ash_wait_chains.sql检查，发现control file parallel write有点多。
--//当时并没有在意，总感觉哪里不对，感觉这套系统磁盘io有问题，现在有空分析看看。
1.环境：
> @ 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.问题提出：
> @ 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) 范围在2020/3/29 2020/3/30 之间,是星期天.
--//很明显这是一套根本不忙的系统(我已经做了许多优化),当然的时间区间也很大，不过还是可以看出服务器不忙。
--//同时很不理解为什么control file parallel write能达到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
--//仅仅进程3831有写。
# ps -ef | grep 383[1]
oracle 3831 1 0 2016 ? 04:13:39 ora_ckpt_xxxyyy
--//正是ckpt进程。
SYS@xxxyyy> show parameter filesystem
NAME TYPE VALUE
-------------------- ------ -------
filesystemio_options string ASYNCH
--//打开了磁盘异步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
--//控制文件对应文件句柄是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
--//你可以发现每秒都调用一次io_submit写入，时间间隔大约1秒1次，实际上就是写增量检查点,数据库很空闲。
0.022249+0.015565+0.016591+0.015069+0.015453+0.014407+0.023324+0.032261+0.081960 = .236879
.236879/9 = .02632,平均占.02632秒。
--//如果换算成毫秒的话,相当于26ms.这是一个相当差劲的IO,我严重怀疑BiOS没有打开写回功能(write back),而是设置在写通模式
--//(write through)上.
--//相当于一天调用 86400 /(1+.02632) = 84184次。需要84184*.02632 = 2215.72288秒,当然这是io_submit的时间,并非control file
--//parallel write.非常接近上面看到control file parallel write=2790秒。
--//再加大取样量看看。
# 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
--//取样42次，0.0248849秒相当于25ms。相当慢的磁盘IO。
4.如何确定磁盘在write back还是write Through状态呢？
--//方法一：首先想到的进入BIOS检查，当然目前不行。
--//方法二：dmesg,没有发现相关信息。
--//方法三：我知道dell随机光盘里面有一个使用程序可以通过浏览器查看硬件配置的程序。这个比较麻烦，机器已经太老了。相关资料
--//放在哪里也不知道。
--//方法四：hdparm，看了一下man文档也没有发现相关设置与检查。
# 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，感觉这个命令很危险DANGEROUS,放弃。
--//方法五：想想linux还有什么命令了解硬件配置呢，马上想到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
--//很明显了安装人员没有很好的设置磁盘操作模式。
# 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:
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
--//找了一台相似的机器检查发现：
# 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
--//基本可以验证我的推断，安装OS的人员没有很好的设置BIOS，设置在Write Through模式导致写入磁盘IO有点慢。
--//要么还有一种可能就是板上可能有电池，已经没电了，无法设置在write back模式。仅仅是我的推断。
5.顺便测试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
检查点队列
当前时间 脏块数量
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, "x15xc2x00x00x01x00x00x00x00x00x00x00x00x00x01x04x15x4cx00x00x00x00x00x00x00x00x20x0bx56x37x09x0f"..., 16384, 16384) = 16384 <0.000024>
09:45:36.707785 pread(257, "x15xc2x00x00x0fx00x00x00xd7x59x19x00xffxffx01x04xa8x3cx00x00x00x47x00x00x00x00x00x00x00x00x00x45"..., 16384, 245760) = 16384 <0.000018>
09:45:36.707888 pread(257, "x15xc2x00x00x11x00x00x00xd7x59x19x00xffxffx01x04xc4x34x00x00x00x00x00x00x00x00x00x00xd6x6axdcx33"..., 16384, 278528) = 16384 <0.000018>
09:45:36.707985 pread(257, "x15xc2x00x00x14x00x00x00xc8x59x19x00xffxffx01x04x2ex77x00x00x0fx00x00x00x9axb2x19x2bx07x00x1cx0a"..., 16384, 327680) = 16384 <0.000017>
09:45:36.708108 pread(257, "x15xc2x00x00x03x00x00x00x00x00x00x00x00x00x01x04x5bx9ax00x00x02x00x00x00x00x00x00x00xe6x01x00x00"..., 16384, 49152) = 16384 <0.000019>
Process 4912 detached
--//异步IO读取使用pread函数吗，数据库没有使用asm原因？
--//参考链接Http://blog.itpub.net/267265/viewspace-2222208/,执行如下：
> @ 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
检查点队列
当前时间 脏块数量
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
--//上下比较，可以发现physical read total IO requests增加5次(278-273=5)，physical read total bytes增加 6915072-6833152=81920,正好等于16384*5= 81920.
--//你可以发现读16384字节 每次pread的时间很小。
总结：
--//再次提醒自己注意一些细节。数据库上线前给仔细检查，实际上还是我提到的分工问题，如果节点上的人做好自己的工作，
--//链接：http://blog.itpub.net/267265/viewspace-2102914/ => [20160519]浅谈行业分工.txt ,这台机器就是当年的这台服务器。
--//实际上如果当时我没有再仔细看，这个问题就给划过了。
--//还有一点要说明的是通过awr报表很容易划过这个问题。
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
--//负载太轻了。不在前台等待事件。
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) ,只能讲自己功力还是不够，没有仔细看这些细节，主要精力放在前台事件的优化上了，忽略后后台事件。
--//磁盘IO存在问题。
--//附上测试脚本：
$ 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 "检查点队列|脏块数量|CPDRT"
column cpodt_on_disk_rba heading "检查点队列|on disk rba|时间戳|CPODT"
column cpods heading "检查点队列|on disk rba scn|CPODS"
column cphbt heading "检查点心跳|CPHBT"
column current_sysdate heading "当前时间|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;
--结束END--
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