一个客户打过来的，说是碰到一个很奇怪的问题。在一张上千万记录的大表里，做一个SELECT * FROM lt;TAB_NAMEgt; WHERE ROWNUM
一个客户打过来的，说是碰到一个很奇怪的问题。在一张上千万记录的大表里，做一个SELECT * FROM call count cpu elapsed disk query currentrows ------- ------ -------- ---------- -------------------- ---------- ---------- Parse 1 0.14 0.17 44 198 0 0 Execute 1 0.00 0.00 0 0 0 0 Fetch 8 3.71 5.86 67489 68340 0 99 ------- ------ -------- -------------------- ---------- ---------- ---------- total 10 3.85 6.03 67533 68538 0 99 从这上面看，确实产生了67533个物理读和68538个逻辑读。执行时间为6.03秒。从等待事件来看： BINDS #39: EXEC #39:c=0,e=88,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,tim=1422207486718 WAIT #39: nam='SQL*Net message to client'ela= 7 driver id=1650815232 #bytes=1 p3=0 obj#=206418 tim=1422207486810 WAIT #39: nam='SQL*Net more data to client'ela= 203 driver id=1650815232 #bytes=2002 p3=0 obj#=206418 tim=1422207487071 WAIT #39: nam='SQL*Net more data to client'ela= 66 driver id=1650815232 #bytes=2020 p3=0 obj#=206418 tim=1422207487175 WAIT #39: nam='db file scattered read' ela=515 file#=146 block#=92900 blocks=5 obj#=206418 tim=1422207488208 WAIT #39: nam='db file scattered read' ela=918 file#=146 block#=92905 blocks=8 obj#=206418 tim=1422207489579 WAIT #39: nam='db file scattered read' ela=2121 file#=146 block#=92914 blocks=7 obj#=206418 tim=1422207492091 WAIT #39: nam='db file scattered read' ela=617 file#=146 block#=92921 blocks=8 obj#=206418 tim=1422207493135 WAIT #39: nam='db file scattered read' ela=493 file#=146 block#=92930 blocks=7 obj#=206418 tim=1422207494016 WAIT #39: nam='db file scattered read' ela=1666 file#=147 block#=897417 blocks=8 obj#=206418 tim=1422207496049 WAIT #39: nam='db file scattered read' ela=1026 file#=147 block#=897426 blocks=7 obj#=206418 tim=1422207497350 WAIT #39: nam='db file scattered read' ela=378 file#=147 block#=897433 blocks=8 obj#=206418 tim=1422207498049 WAIT #39: nam='db file scattered read' ela=1075 file#=147 block#=897442 blocks=7 obj#=206418 tim=1422207499416 WAIT #39: nam='db file scattered read' ela=1649 file#=147 block#=897449 blocks=3 obj#=206418 tim=1422207501237 WAIT #39: nam='db file scattered read' ela=2768 file#=147 block#=897453 blocks=4 obj#=206418 tim=1422207504191 WAIT #39: nam='db file scattered read' ela=653 file#=147 block#=897458 blocks=7 obj#=206418 tim=1422207505141 WAIT #39: nam='db file scattered read' ela=1588 file#=147 block#=897465 blocks=8 obj#=206418 tim=1422207507029 WAIT #39: nam='db file scattered read' ela=460 file#=147 block#=897474 blocks=7 obj#=206418 tim=1422207507787 WAIT #39: nam='db file scattered read' ela=608 file#=147 block#=897481 blocks=8 obj#=206418 tim=1422207508697 WAIT #39: nam='db file scattered read' ela=564 file#=147 block#=897490 blocks=7 obj#=206418 tim=1422207509571 WAIT #39: nam='db file scattered read' ela=832 file#=147 block#=897497 blocks=8 obj#=206418 tim=1422207510668 WAIT #39: nam='db file scattered read' ela=846 file#=148 block#=102411 blocks=16 obj#=206418 tim=1422207512030 WAIT #39: nam='db file scattered read' ela=4872 file#=148 block#=102427 blocks=16 obj#=206418 tim=1422207517488 WAIT #39: nam='db file scattered read' ela=1624 file#=148 block#=102443 blocks=16 obj#=206418 tim=1422207520062 确实存在大量的DB FILE SCATTERD READ。这更加坚信了我的观点，表里存在大量的碎片。找第一个SCATTERD READ的参数 file#=146 block#=92900，让客户执行alter system dump datafile 146 block min 92900 block max 92904。
获得的结果如下：
data_block_dump,data header at0x6000000000208e64
===============
tsiz: 0x1f98
hsiz: 0x4c
pbl: 0x6000000000208e64
bdba: 0x24816ae4 76543210
flag=--------
ntab=1
nrow=29
frre=0
fsbo=0x4c
fseo=0xf7
avsp=0x1f4c
tosp=0x1f4c
0xe:pti[0] nrow=29 offs=0
0x12:pri[0] sfll=1
0x14:pri[1] sfll=2
0x16:pri[2] sfll=3
0x18:pri[3] sfll=4
0x1a:pri[4] sfll=5
0x1c:pri[5] sfll=6
0x1e:pri[6] sfll=7
0x20:pri[7] sfll=8
0x22:pri[8] sfll=9
0x24:pri[9] sfll=10
0x26:pri[10] sfll=11
0x28:pri[11] sfll=12
0x2a:pri[12] sfll=13
0x2c:pri[13] sfll=14
0x2e:pri[14] sfll=15
0x30:pri[15] sfll=16
0x32:pri[16] sfll=17
0x34:pri[17] sfll=18
0x36:pri[18] sfll=19
0x38:pri[19] sfll=20
0x3a:pri[20] sfll=21
0x3c:pri[21] sfll=22
0x3e:pri[22] sfll=23
0x40:pri[23] sfll=24
0x42:pri[24] sfll=25
0x44:pri[25] sfll=26
0x46:pri[26] sfll=27
0x48:pri[27] sfll=28
0x4a:pri[28] sfll=-1
block_row_dump:
end_of_block_dump
里面全部是空块。建议客户做一个ALTER TABLE
What Are the Limitations of Using Views in MySQL?May 14, 2025 am 12:10 AMMySQLviewshavelimitations:1)Theydon'tsupportallSQLoperations,restrictingdatamanipulationthroughviewswithjoinsorsubqueries.2)Theycanimpactperformance,especiallywithcomplexqueriesorlargedatasets.3)Viewsdon'tstoredata,potentiallyleadingtooutdatedinforma
Securing Your MySQL Database: Adding Users and Granting PrivilegesMay 14, 2025 am 12:09 AMProperusermanagementinMySQLiscrucialforenhancingsecurityandensuringefficientdatabaseoperation.1)UseCREATEUSERtoaddusers,specifyingconnectionsourcewith@'localhost'or@'%'.2)GrantspecificprivilegeswithGRANT,usingleastprivilegeprincipletominimizerisks.3)
What Factors Influence the Number of Triggers I Can Use in MySQL?May 14, 2025 am 12:08 AMMySQLdoesn'timposeahardlimitontriggers,butpracticalfactorsdeterminetheireffectiveuse:1)Serverconfigurationimpactstriggermanagement;2)Complextriggersincreasesystemload;3)Largertablesslowtriggerperformance;4)Highconcurrencycancausetriggercontention;5)M
MySQL: Is it safe to store BLOB?May 14, 2025 am 12:07 AMYes,it'ssafetostoreBLOBdatainMySQL,butconsiderthesefactors:1)StorageSpace:BLOBscanconsumesignificantspace,potentiallyincreasingcostsandslowingperformance.2)Performance:LargerrowsizesduetoBLOBsmayslowdownqueries.3)BackupandRecovery:Theseprocessescanbe
MySQL: Adding a user through a PHP web interfaceMay 14, 2025 am 12:04 AMAdding MySQL users through the PHP web interface can use MySQLi extensions. The steps are as follows: 1. Connect to the MySQL database and use the MySQLi extension. 2. Create a user, use the CREATEUSER statement, and use the PASSWORD() function to encrypt the password. 3. Prevent SQL injection and use the mysqli_real_escape_string() function to process user input. 4. Assign permissions to new users and use the GRANT statement.
MySQL: BLOB and other no-sql storage, what are the differences?May 13, 2025 am 12:14 AMMySQL'sBLOBissuitableforstoringbinarydatawithinarelationaldatabase,whileNoSQLoptionslikeMongoDB,Redis,andCassandraofferflexible,scalablesolutionsforunstructureddata.BLOBissimplerbutcanslowdownperformancewithlargedata;NoSQLprovidesbetterscalabilityand
MySQL Add User: Syntax, Options, and Security Best PracticesMay 13, 2025 am 12:12 AMToaddauserinMySQL,use:CREATEUSER'username'@'host'IDENTIFIEDBY'password';Here'showtodoitsecurely:1)Choosethehostcarefullytocontrolaccess.2)SetresourcelimitswithoptionslikeMAX_QUERIES_PER_HOUR.3)Usestrong,uniquepasswords.4)EnforceSSL/TLSconnectionswith
MySQL: How to avoid String Data Types common mistakes?May 13, 2025 am 12:09 AMToavoidcommonmistakeswithstringdatatypesinMySQL,understandstringtypenuances,choosetherighttype,andmanageencodingandcollationsettingseffectively.1)UseCHARforfixed-lengthstrings,VARCHARforvariable-length,andTEXT/BLOBforlargerdata.2)Setcorrectcharacters
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
SublimeText3 Linux new version
SublimeText3 Linux latest version
SecLists
SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.
ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment
DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software
Notepad++7.3.1
Easy-to-use and free code editor
