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linux内存cached释放 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...缩短了 I/O系统调用(比如read,write,getdents)的时间。"
如何解决这个导致机器变慢的问题呢？
罪魁祸首就是内存都被cached了，free的基本没有了
所以我们应该想想如何把cached内存释放出来
重启机器肯定是可以解决，但是我们...
SQL WITH clause example [duplicate]
...loyee AS (SELECT * FROM Employees)
SELECT * FROM employee WHERE ID < 20
UNION ALL
SELECT * FROM employee WHERE Sex = 'M'
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SQL select only rows with max value on a column [duplicate]
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I know that MySQL allows you to add non aggregate fields to a "grouped by" query, but I find that kinda pointless. Try running this select id, max(rev), rev from YourTable group by id and you see what I mean. Take your time and try to un...
How to test an SQL Update statement before running it?
...What about Transactions? They have the ROLLBACK-Feature.
@see https://dev.mysql.com/doc/refman/5.0/en/commit.html
For example:
START TRANSACTION;
SELECT * FROM nicetable WHERE somthing=1;
UPDATE nicetable SET nicefield='VALUE' WHERE somthing=1;
SELECT * FROM nicetable WHERE somthing=1; #check
CO...
How to add 'ON DELETE CASCADE' in ALTER TABLE statement
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Answer for MYSQL USERS:
ALTER TABLE ChildTableName
DROP FOREIGN KEY `fk_table`;
ALTER TABLE ChildTableName
ADD CONSTRAINT `fk_t1_t2_tt`
FOREIGN KEY (`parentTable`)
REFERENCES parentTable (`columnName`)
ON DELETE CASCADE
ON UP...
What are the use cases of Graph-based Databases (http://neo4j.org/)? [closed]
... team actually rewrote the database layer to use Oracle (or PostgreSQL, or MySQL), but it was slightly slower than the original. At least one large enterprise even had an Oracle-only policy, but luckily Oracle bought Berkeley DB. We also had to write a lot of extra tools - we couldn't just use Cryst...
Spring Boot - Cannot determine embedded database driver class for database type NONE
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spring.datasource.url = jdbc:mysql://localhost/abc #spring.datasource.driverClassName = com.mysql.jdbc.Driver spring.datasource.name=olabsenglishdb spring.datasource.username=xxxx spring.datasource.password=xxxx spring.datasource.driver-class-name= com.m...
How do I select an entire row which has the largest ID in the table?
...show profiles and it appears our solutions have the same performance using MySQL. For my own knowledge, do you know what DBMS has poorer performance for subselects?
– unutbu
Feb 7 '14 at 20:08
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How to use JNDI DataSource provided by Tomcat in Spring?
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auth="Container"
type="javax.sql.DataSource"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/TestDB"
username="pankaj"
password="pankaj123"
maxActive="100"
maxIdle="20"
minIdle="5"
maxWait="10000"/>
back to context.xml de spring add this
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JPA: unidirectional many-to-one and cascading delete
...solution to why delete was not working. apparently hibernate was NOT using mysql Engine -INNODB , you need engine INNODB for mysql to generate foreign key constraint. Using the following properties in application.properties, makes spring boot/hibernate to use mysql engine INNODB. So foreign key co...