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查看InnoDB的磁盘空间利用率 page利用率主要是指btee里面每个page的使用被使用的空间大小。我们知道InnoDB默认一个page大小是16k。但实际使用情况不会总用满我们定义为所有page的总使用字节除以总字节数。在理论分析之前，我们要先弄个工具，查一下。 实例统计写了一个简单的工具，读ibd文件上的每个page，算出每个page的实际使用字节，可以得到利用率。我们找了线上一个库来模拟。表中有1个自增主键和3个非聚簇索引。不影响结论地简化为如下：CREATE TABLE `ctu_factor_risk_99_03` (`seq_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,`a` varchar(32) DEFAULT NULL,`b` varchar(32) DEFAULT NULL,`c` varchar(32) DEFAULT NULL,KEY a (a),KEY bc (b,c),KEY cb (c,b),) ENGINE=InnoDB DEFAULT CHARSET=utf8; 插入数据中a,b,c均为长度为30字节的随机字符串。 显然主键和其他索引应该分开统计。统计结果发现，主键page利用率71%，其他索引利用率约52%。 简单分析上面的结果很好理解。因为按照主键递增顺序插入数据，因此主键上数据“紧凑”。 而其他三个索引，则都是随机更新，需要不停地作索引节点分裂。 如何提升磁盘空间利用率回到最开始的问题。其实我们关心的，是InnoDB为了保存相同的数据，用了多少空间。所以我们的问题变成，存储相同的数据，如何让占用的磁盘空间更小。 有一个很直观的结论。把这些索引删了重建，必然会减少空间消耗。因为这个操作之后，在新的数据插入之前，这些索引也变成“紧凑的”。 再建了一个与cb相同的索引，再跑，利用率居然高达98%。这个原理大家应该都知道了，只是量化一下而已。 工具附后， 用法 ./ibd_used tb.ibd N1 N2 >/tmp/r 最后几行为各个索引的利用率统计值 （附件）ibd_used.rar http:///uploadfile/2012/0429/20120429085005514.rar 作者 丁林.tb bitsCN.com
MySQL String Types: Storage, Performance, and Best PracticesMay 10, 2025 am 12:02 AMMySQLstringtypesimpactstorageandperformanceasfollows:1)CHARisfixed-length,alwaysusingthesamestoragespace,whichcanbefasterbutlessspace-efficient.2)VARCHARisvariable-length,morespace-efficientbutpotentiallyslower.3)TEXTisforlargetext,storedoutsiderows,
Understanding MySQL String Types: VARCHAR, TEXT, CHAR, and MoreMay 10, 2025 am 12:02 AMMySQLstringtypesincludeVARCHAR,TEXT,CHAR,ENUM,andSET.1)VARCHARisversatileforvariable-lengthstringsuptoaspecifiedlimit.2)TEXTisidealforlargetextstoragewithoutadefinedlength.3)CHARisfixed-length,suitableforconsistentdatalikecodes.4)ENUMenforcesdatainte
What are the String Data Types in MySQL?May 10, 2025 am 12:01 AMMySQLoffersvariousstringdatatypes:1)CHARforfixed-lengthstrings,2)VARCHARforvariable-lengthtext,3)BINARYandVARBINARYforbinarydata,4)BLOBandTEXTforlargedata,and5)ENUMandSETforcontrolledinput.Eachtypehasspecificusesandperformancecharacteristics,sochoose
How to Grant Permissions to New MySQL UsersMay 09, 2025 am 12:16 AMTograntpermissionstonewMySQLusers,followthesesteps:1)AccessMySQLasauserwithsufficientprivileges,2)CreateanewuserwiththeCREATEUSERcommand,3)UsetheGRANTcommandtospecifypermissionslikeSELECT,INSERT,UPDATE,orALLPRIVILEGESonspecificdatabasesortables,and4)
How to Add Users in MySQL: A Step-by-Step GuideMay 09, 2025 am 12:14 AMToaddusersinMySQLeffectivelyandsecurely,followthesesteps:1)UsetheCREATEUSERstatementtoaddanewuser,specifyingthehostandastrongpassword.2)GrantnecessaryprivilegesusingtheGRANTstatement,adheringtotheprincipleofleastprivilege.3)Implementsecuritymeasuresl
MySQL: Adding a new user with complex permissionsMay 09, 2025 am 12:09 AMToaddanewuserwithcomplexpermissionsinMySQL,followthesesteps:1)CreatetheuserwithCREATEUSER'newuser'@'localhost'IDENTIFIEDBY'password';.2)Grantreadaccesstoalltablesin'mydatabase'withGRANTSELECTONmydatabase.TO'newuser'@'localhost';.3)Grantwriteaccessto'
MySQL: String Data Types and CollationsMay 09, 2025 am 12:08 AMThe string data types in MySQL include CHAR, VARCHAR, BINARY, VARBINARY, BLOB, and TEXT. The collations determine the comparison and sorting of strings. 1.CHAR is suitable for fixed-length strings, VARCHAR is suitable for variable-length strings. 2.BINARY and VARBINARY are used for binary data, and BLOB and TEXT are used for large object data. 3. Sorting rules such as utf8mb4_unicode_ci ignores upper and lower case and is suitable for user names; utf8mb4_bin is case sensitive and is suitable for fields that require precise comparison.
MySQL: What length should I use for VARCHARs?May 09, 2025 am 12:06 AMThe best MySQLVARCHAR column length selection should be based on data analysis, consider future growth, evaluate performance impacts, and character set requirements. 1) Analyze the data to determine typical lengths; 2) Reserve future expansion space; 3) Pay attention to the impact of large lengths on performance; 4) Consider the impact of character sets on storage. Through these steps, the efficiency and scalability of the database can be optimized.
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