Database Administrator

Conclusion: I. Six methods for obtaining an execution plan (the detailed steps are described in the remarks section at the beginning of each example ):1. Obtain the explain plan for statement;2. set autotrace on;3. statistics_level = all;4. Use dbms_

In general, in the future, we will prevent users from deleting or clearing tables and data. You can directly grant them a small amount of permissions.For example, to prevent users from performing truncate operations, you can grant the following

In the OLTP system, nested connections account for about 70%, hash connections account for 20%, and merge sorted connections account for 10%.Nested connection Algorithm: Nested join selects a small table as the driver table from two tables, and a

1. MapReduce Architecture MapReduce is a programmable framework. Most MapReduce jobs can be completed using Pig or Hive, but we still need to know how MapReduce works, because this is the core of Hadoop, you can also prepare for optimization and

Three Hadoop installation modes: 1. Stand Alone Mode. All Hadoop instances run in one jvm. 2. Psuedo Distributed Mode all Hadoop instances run in different JVMs (this course) 3. Fully Distributed Mode each instance runs on its own machine   1.

Because the data capacity is smaller than 20 GB, using mysqldump for full-Database Export has little impact on the business. Therefore, this mode is used to build a slave database: PS: master-data = 1, record the Master_Log_File and Read_Master_Log_

The last time I took a note, I learned how to query multiple tables. This time I took a note to learn about grouping functions in Oracle. First, let's take a look at what group functions are: Group function: acts on a group of data and returns a

Inner join Operator The inner join keyword returns a row if there is at least one match in the table. SQL INNER JOIN syntax SELECT column_name (s) FROM table1INNER JOIN table2ON table1.column _ name = table2.column _ name; Or: SELECT

Indexing is a powerful weapon to improve database query performance. Without an index, it is like a library without a book tag. It is more difficult to find a book you want than to climb to the sky. However, in the process of using indexes,

After a few days of study, you can basically try to write some small programs to play with it. Before that, do a few preparations. A: My first response to big data is how the data in the existing relational database can be used in combination

1.1 symptom description Query the Process status of the SQL statement executed by the database and find that the SQL statement execution process is deadlocked. The system displays the following information: SQL> select address, SQL _text, piece,

Problem: The float momey type in the database is precise to multiple decimal places. But sometimes we don't need to be so precise. For example, we only need to be accurate to two valid numbers. Solution: 1. Use the Round () function. For example,

Install the binary version of MongoDB 6.5 in CentOS 2.6 By chszs. Blog homepage: http://blog.csdn.net/chszsThe access to foreign MongoDB images is very slow, so it is very unreliable to select the MongoDB official website for online installation.

Solution to paip. hibernate save failureOpen log debug level, and you cannot see the insert code...Hibernate select max(ID).txtIt is worth noting that the save () method does not immediately execute the SQL insert statement. The SQL insert statement

Yesterday's index came across ORA-00054: the problem of resource busy and acquire with NOWAIT specified, which took a lot of time to solve. This error is actually very simple. In this case, the user has not committed the transaction to this table,

I learned the operations related to query and create a management table from my previous notes. This time, I learned how to process data, including inserting data into the table and updating data) and DELETE data ). To save the original data of emp,

The robustness after Oracle RAC is installed is a headache. Oracle previously launched a dedicated raccheck tool for it, which makes it easy for us to use these hard-pressed DBAs. Now, Oracle has launched the license HK on the basis of raccheck.

I have been entangled in the implementation of the database connection pool. Today, I have finally squeezed out time to implement it. Before tomcat, the connection pool was implemented using dbcp. dbcp has many disadvantages. Currently, tomcat uses

Someone asked me about saiku's Chinese Query: By default, saiku runs in English. Many users enter Chinese Characters in mysql and use SQL to query data. However, if you use the mdx query function of saiku, an error is returned. This is because

A problem occurs at work: update a data table. This table is created by myself and has seven fields: id, name, package, etc. During creation, because I saved the name and package information in two text files, So I will use the Insert method to