microgrid concept

UNCOMMITTED transaction isolation LEVEL only skip RID lock, skip page, zone and table lockRowlock forcing the use of row locksTablockx enforces exclusive table-level locks, which prevent any other transactions from using this table during a transactionUplock forcing updates to be used when reading tables without sharing locksApplication Lock:The application lock is the lock generated by the client code, not the lock generated by SQL Server itselfTwo procedures for handling application locksSp_g

Tags: Database thinking map SummaryConceptual model:(1) The overall logical structure of the data is expressed, which is a comprehensive description of the data involved in the whole application project by the system user. Overall(2) The data is modeled from the point of view of the user's needs. View(3) Independent of hardware and software. Independence(4) is a tool for communication between the Database Designer and the user. ToolsLogical Model:(1) The overall logical structure of the DB is ex

speed will drop more obviously.F, and the full text search generally, with the increase in data volume, the decline can not be so obvious.There are three ways to implement full-text search in PHP. One is the full-text search function of the MySQL MyISAM engine. The second is to use the Sphinx with MySQL tightly.Third, the use of a more professional full-text search engine. Lucene. and use Slor to achieve the volume of inquiry.Download SOLRWget-c Http://mirrors.cnnic.cn/apache/lucene/solr/4.8.1/

connecting instructor and department to Dept_name, to get information from each mentor and his departmentCartesian product XThe Cartesian product outputs all the tuple pairs, such as the Cartesian product of the teacher and the department, indicating all possible correspondence.And ∪The parallel operation merges two tables with similar structures.For duplicate data in the result of the operation, some SQL languages strictly follow the mathematical definition of set operations to remove duplicat

Tags: relationship DB2 problem complete ble run SQL very saveDatabase features: Mass storage, fast lookup, concurrency problem control, security, data integrity (the data stored in the database is correct, real).Table: [Relationships] in a relational database are tables. Different brands of DBMS have their own different features: MySQL (fast, suitable for the data requirements are not very rigorous place, removed many small and medium-sized enterprises infrequently used features),MSSQLServer (an

',20000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',30000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',40000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',50000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',60000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',70000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',80000); Insert into Scott.EmpValues(1,'Baoxinjian1','M', -,' China',90000);End;comm

SQL Terminology/Concepts MongoDB Terminology/Concepts Explanation/Description Database Database Database Table Collection Database Tables/Collections Row Document Data record lines/documents Column Field Data fields/Fields Index Index Index Table joins Table connection, MongoDB not supported Primary key Primary key

because of the following decision relationship: (school number) → (school) → (college location, college phone) That is, there is a non-critical field "College location", "College phone" to the key field "study number" of the transfer function dependency. It also has data redundancy, update exceptions, insert exceptions, and delete exceptions, which readers can analyze on their own. The Student relations table is divided into the following two tables: Student: (School number, name, age, school);

Server Process Concepts: Oracle's server process has an Oracle instance created automatically to handle requests from the client process connected to the instance, and the user must obtain information from the database through a server process connected to Oracle. For dedicated server mode (default when building a library), the client process and the Oracle server process are one by one corresponding, add a server process, approximately the required memory is: AIX 5-10m, LINUX 3-5m memory-meas

First, the concept of iSCSI iSCSI is a standard for data block transmission on Internet protocols, especially Ethernet, which is a new storage technology based on IP storage theory, which combines SCSI interface technology widely used in storage industry with IP network technology, You can build a SAN storage area network on an IP network, simply put, iSCSI is a networked storage technology that runs SCSI protocols on an IP network. iSCSI technology

will consume b*tt+s*ts seconds. Now the typical value of the disk is Tt = 0.1 milliseconds, ts = 4 milliseconds, assuming that the disk block size is 4KB, the transfer rate is 40mb/seconds.by separating the read operation from the write operation, the write operation takes approximately twice times as much time as the read operation, since the disk system reads the data again to verify that the write was successful. Learning materials: Database System concepts, by Abraham Silberschatz, Henry

there are more attributes, the length of the empty graph needs to be expanded. This method saves storage space at the expense of additional empty graph reads, and is useful in tables with many attributes and many of these properties being null. B) storing variable length records in blocksWhen storing variable-length records in a block, the slot structure (slotted-page structure) is typically used for paging, with headers in each block: The header contains information about the number of entri

the records to be centrally mapped to some buckets, and a bucket can hold records that are limited, which is known as bucket skew ( Bucket skew).In order to deal with bucket overflow, you can leave a certain amount in the determination of buckets, but this will cause space waste; You can also use an overflow bucket (overflow bucket) to receive overflow records: Once an overflow occurs, a new overflow bucket is added to receive the overflow record. The overflow bucket and the original bucket for

clustered index, should be as far as possible the value of continuous growth, rather than random values,(Do not use random strings or UUID)Doing so will result in a large number of page splits and page movements.　　In order to see the effect, you can insert 1000 data into the database by inserting 1000 data in order and disorderly order in Java. Look at the time of execution to see the effect.such as:Innodb_pages_written represents the number of pages that have been written, you can insert 1000

Python has been an object-oriented language since its inception, which is why it is easy to create a class and object in Python. In this article, I'll cover Python's object-oriented knowledge in detail. If you have not been exposed to object-oriented programming languages before, you may need to first understand some of the basic features of object- oriented languages and form a basic object-oriented concept in your mind, which will help you learn

 Reprint Please specify source: http://www.cnblogs.com/fangkm/p/4401075.html The first two blog posts complete the WEBRTC audio and video collection module, and the next step is to introduce the key audio and video coding modules. However, before introducing the audio and video coding module, we need to introduce the channel concept, and the transmission flow of each WEBRTC data is encapsulated into a channel object. The detailed UML diagram is as

join? Leave the left, right, and all unmatched rows separately.The equivalent expression for the left outer join is:(R?s) ∪ (R-πr (R?s)) x{(null,... NULL)}where {(null,... null)} is a schema after s-re) Extended operationGeneralized projection (generalized Projection)Generalized projections allow the operation of arithmetic and string processing at the same time as projection operations, such as:ΠID,NAME,SALARY*13 (instructor)Aggregation (aggregation)Aggregation includes operations such as Min,

only to the role of the transition, do not need to save data, so the block hole engine for this intermediate from the server, so that no data saved, but the trunk log and the binary log are normally saved, The effect of the transition.Cyclic replication, in multi-master mode, uses cyclic replication, but the chain is longer and can result in severe data lag.Dual master replication;Semi-synchronous replication:One from the multi-master model: Each master server provides a different database, mas

include "early execution of selection operations", "early execution of projection operations", "avoiding Cartesian product operations" and so on.You can also use materialized views to speed up query processing. When the original relationship changes, the materialized view needs to be updated efficiently with incremental view maintenance. By using an algebraic expression that contains the amount of change in an input of an operation, the amount of change in the operation can be calculated. Other

Label:Key type:1. Primary key2. Unique key3. Foreign keyIndex Type:1. Hash index2. Ordered index (btree/rtree)Creation of the index:1. Primary key creates two indexes: Hash index and ordered index2. Unique key creates two indexes: Hash index and ordered index3. Generally defined indexes create only ordered indexesPrimary key and unique key each index uses the scene:1. When the operation type is =, use the hash index2. When the operation type is range, use the ordered indexIndex usage principles: