Database Administrator

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

Principle of Bitmap IndexingAdvantages of Bitmap indexes1. Quick statisticsBecause Bitmap indexes only store 0 and 1 fingers, the space occupied by Bitmap indexes is very small, and operations such as count (*) are very fast.2. Efficient ad hoc

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_

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,

1.1 symptom description The response of database nodes is slow, and some user services are affected. View database alarm logs and start to displayORA-07445Errors, followed by a large numberORA-04031Errors andORA-00600Error. Check the database logs.

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,

Database objects include tables, views, sequences, indexes, and synonyms. The tables and views are learned in the previous notes. Database objects, that is, sequences, indexes, and synonyms. Sequence: provides regular values. Database objects that

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,

InfiniDB cannot create a table. The following error is returned when creating a table: First error: Constraint is not supported by InfiniDB. This is a constraint in SQL statements, which is not supported by infiniDB. For example Create table

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

1. Index The index is for the database tableOne or more columnsA structure in which values are sorted. You can use indexes to quickly access specific information in database tables. The purpose of creating an index is to speed up the recordSearch

The index quality has a direct impact on the overall performance of the database. Good and high-quality indexes increase the database performance by an order of magnitude, while inefficient and redundant indexes make the database performance slow,

Database migration In software development, we have version managers such as svn and git to help us manage the source code. We can easily view the version of our current code, update the new version code, roll back to the old version, and so on. If

[Java] [MyBatis] physical paging implementation Mybatis3.0 has been out for a while. In fact, I like this persistence framework because it is simple and practical and has a low learning cost. The overall structure of Mybatis3.0 is similar to that of

 An analysis of pga abnormal consumption OS: aix 6 Db: 10205 ------ Use the OS command to observe the memory consumption of oracle Processes# Ps gv... Size23396516-A 14907: 02 5203 14324376 2058800 xx 90815 38576 2.0 oracle23396516-A 14907: 02 5203

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,