Read about mysql varchar length performance, The latest news, videos, and discussion topics about mysql varchar length performance from alibabacloud.com
the number of rows in each table! That is, the total number of rows processed here is 74*2135*74*3872 = 45,268,558,720.
One of the problems here is that, if the declaration of the database column is different, MySQL (also) cannot effectively use the column index. In this case, VARCHAR and CHAR are the same unless they have different declared lengths. Because tt. ActualPC declares CHAR (10), and et. empl
is often better than int because the Mediumint column uses 25% less space.4) If possible, the declaration is listed as not NULL. It makes everything faster and saves one per column. Note If you do need null in your application, you should use it without question, just avoid having it on all columns by default.5 for MyISAM tables, if there are no variable-length columns (VARCHAR, text, or BLOB columns), use
purpose of the flow queue data is to determine the data in the table where the data will be keptis insert,update and delete, and each operation generates the corresponding log information. In MySQL, if theThe storage engine that holds the transaction, the amount of this log generation is doubled. And if we go through some mature third-party queue software toThe performance of this queue data processing fun
record (index map:n): No good index.three . Index and query optimization1. Types of indexesØ Normal Index: This is the most basic index type, no uniqueness, and so on.Ø Uniqueness Index: Basically the same as a normal index, but all index column values remain unique.Ø PRIMARY key: The primary key is a unique index, but must be specified as "PRIMARY key".Full-Text indexing: MySQL supports full-text indexing and full-text retrieval starting from 3.23.
length field. In addition, this will bring you query advantages, especially when you need to use the WHERE condition: IP between ip1 and ip2. We must use the unsigned int, because the IP address will use the entire 32-bit UNSIGNED integer. 15. A table with a fixed length will be faster. If all the fields in the table are "fixed length", the whole table will be c
performance boost that is relatively small. If you plan to build indexes on columns, you should try to avoid designing nullable columns. Of course there are exceptions: InnoDB uses a separate bit to store null values, so there is a good space efficiency for sparse data (many values are null).1, Integer typeTINYINT 8SMALLINT 16Mediumint 24INT 32BIGINT 64An optional unsigned of integer type indicates that a negative number is not allowed, so that a pos
supported, but the indexes are read-only.MySQL built-in other storage engine
Archive: Suitable for high speed insertion , quick insert.
blackhole: There is no storage mechanism, he discards all inserted data, but the server logs the table log, so it can be used to copy the data to the repository, or simply to log.
CSV: You can process a normal CSV file as a MySQL table, which does not support indexing. The CSV engine can copy or copy
The static format is the default storage format for MyISAM tables. Use this format when the table does not contain variable length columns (VARCHAR, blobs, or text). Each row is stored with a fixed byte number.
Of the three storage formats for MyISAM, the static format is the simplest and safest (at least for crashes). The static format is also the fastest on-disk format. A quick way to get the rows from a
whatever you need. 8. Always set an ID for each table We should set an ID for each table in the database as its primary key, and the best is an int type (recommended to use unsigned), and set the automatically added Auto_increment flag. Even if you have a field in the users table that has a primary key called "email", you don't have to make it a primary key. Use the VARCHAR type to degrade performance when
Mysql optimization and mysql Performance Optimization
For a data-centric application, the quality of the database directly affects the performance of the program, so the database performance is crucial. I
To ensure database efficiency, do the following:
① Database Design
② S
In the MySQL execution plan:IDID used to indicate the order of execution, ID the same as a group, first execute ID A large number of groups, and then a small group of numbers are executed. within a group with the same ID, the order is executed from top to bottom. TypeIndicates how MySQL finds the desired row in the table, also known as the "access type", the common types are as follows:From left to right,
execute. You can use unbuffered queries to change this behavior. Save the IP address as UNSIGNED INT Many programmers will create a VARCHAR field to hold IP in the form of a string instead of a shaped IP. If you use plastic to store it, you only need 4 bytes, and you can have a fixed-length field. And, this will bring you the advantage of querying, especially when you need to use such a WHERE condition:I
-engine = InnoDB // The default data table Type of the new data table. The default value is MyISAM.
Lower_case_table_names = 1 // MySQL implementation is case insensitive
Transaction_isolation = REPEATABLE-READ // sets the default transaction isolation level for all connections
Tmp_table_size = 256 M // Maximum length of the temporary HEAP data table
The default value is 32 MB. Temporary data tables tha
"NULL columns require additional space in the row to record whether their values is null. For MyISAM tables, each of the NULL column takes one bit extra, rounded up to the nearest byte. "
12. Save the IP address as UNSIGNED INT很多程序员都会创建一个 VARCHAR(15) 字段来存放字符串形式的IP而不是整形的IP。如果你用整形来存放,只需要4个字节,并且你可以有定长的字段。而且,这会为你带来查询上的优势,尤其是当你需要使用这样的WHERE条件:IP between ip1 and ip2。 We have to use unsigned INT because the IP address uses the entire 32-bit un
used, this rule is also applicable to MYSQL and mainly includes VARCHAR and CHAR string types. The Storage engine determines the Storage methods of these two string types on disk and memory, different storage engines may have different storage methods. Generally, for a storage engine, the storage methods in disks and memory are also different. when data is transferred between disks and memory, storage engi
to the static length type. the storage length is calculated based on the number of characters. Therefore, the final storage length is based on the character set, for example, if latin1 is used, the maximum storage length is 255 bytes, but if gbk is used, the maximum storage length
Implemented by PostGresql open source database, and both systems are implemented by MapReduce theory.Although these two systems are not as scalable as the previous two distributed computing frameworks at present, they are targeted at real DB scenarios, and data access interfaces fully implement SQL specifications. It is no doubt tempting to use the analysis methods used to play the database through SQL statements. What's more, these two systems basically do not need to be developed and are alre
index, in fact, through a certain hash algorithm, will need to index the key value of the hash operation, and then the resulting hash value into a hash table. Then each time you need to retrieve, the search criteria will be the same hash of the algorithm, and then the hash table and the hash value to compare and obtain the corresponding information.Hash index can only meet "=", "in" and "Hash index can not be exploited to avoid the sorting operation of data;The hash index cannot use partial ind
, I will not send out.
Now the MySQL and InnoDB engines are all Oracle's.
MySQL's storage engine
The main two are InnoDB, MyISAM. There are also some built-in engines: Archive, Blackhole, CSV, Federated, Memory, and a few third-party engines are not listed.
Get table information
Use the Command Show table status like ' tablename ' \g to get information about the table.
Several columns of inform
indexed, and then stores the obtained Hash values in a Hash table. Then, each time the search is required, the search conditions are Hash calculated based on the same algorithm, and then compared with the Hash value in the Hash table to obtain the corresponding information.
Hash indexes can only meet "=", "IN", and "
Hash indexes cannot be used to avoid data sorting;
Hash indexes cannot be queried using some index keys;
Hash indexes cannot avoid table scanning at any time;
When the Hash index e
The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion;
products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the
content of the page makes you feel confusing, please write us an email, we will handle the problem
within 5 days after receiving your email.
If you find any instances of plagiarism from the community, please send an email to:
info-contact@alibabacloud.com
and provide relevant evidence. A staff member will contact you within 5 working days.