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Partition (database)
A partition is a division of a logical database or its constituent elements into distinct independent parts. Database partitioning is normally done for manageability, performance or availability reasons, or for load balancing. It is popular in distributed database management systems, where each partition may be spread over multiple nodes, with users at the node performing local transactions on the partition. This increases performance for sites that have regular transactions involving certain views of data, whilst maintaining availability and security. Partitioning criteria Current high-end relational database management systems provide for different criteria to split the database. They take a ''partitioning key'' and assign a partition based on certain criteria. Some common criteria include: * Range partitioning: selects a partition by determining if the partitioning key is within a certain range. An example could be a partition for all rows where the "zipcode" column has a va ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Adminer04
Adminer (formerly known as phpMinAdmin) is a tool for managing content in databases. It natively supports MySQL, MariaDB, PostgreSQL, SQLite, MS SQL, Oracle, Elasticsearch and MongoDB. Adminer is distributed under Apache license (or GPL v2) in a form of a single PHP file (around 470 KiB in size). Its author is Jakub Vrána who started to develop this tool as a light-weight alternative to phpMyAdmin, in July 2007. Adminer got some attention in 2008 when it made it to the CCA finals at SourceForge. Also, first webhosting providers started to include Adminer as MySQL managing tool into their portfolio of services. In 2012 Adminer got coverage on Linux.com for the second time. The project's priorities, according to its author, are (in this order): safety, user-friendliness, performance, functionality, and size. Features * Users log in specifying the destination server and providing the user name and password (which is stored during whole session) * Basic functions: select databas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Transaction
A database transaction symbolizes a unit of work, performed within a database management system (or similar system) against a database, that is treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database. Transactions in a database environment have two main purposes: # To provide reliable units of work that allow correct recovery from failures and keep a database consistent even in cases of system failure. For example: when execution prematurely and unexpectedly stops (completely or partially) in which case many operations upon a database remain uncompleted, with unclear status. # To provide isolation between programs accessing a database concurrently. If this isolation is not provided, the programs' outcomes are possibly erroneous. In a database management system, a transaction is a single unit of logic or work, sometimes made up of multiple operations. Any logical calculation done in a consistent mode in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shard (database Architecture)
A database shard, or simply a shard, is a horizontal partition of data in a database or search engine. Each shard is held on a separate database server instance, to spread load. Some data within a database remains present in all shards, but some appear only in a single shard. Each shard (or server) acts as the ''single'' source for this subset of data. Database architecture Horizontal partitioning is a database design principle whereby '' rows'' of a database table are held separately, rather than being split into columns (which is what normalization and vertical partitioning do, to differing extents). Each partition forms part of a shard, which may in turn be located on a separate database server or physical location. There are numerous advantages to the horizontal partitioning approach. Since the tables are divided and distributed into multiple servers, the total number of rows in each table in each database is reduced. This reduces index size, which generally improves ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Striping
In computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, so that consecutive segments are stored on different physical storage devices. Striping is useful when a processing device requests data more quickly than a single storage device can provide it. By spreading segments across multiple devices which can be accessed concurrently, total data throughput is increased. It is also a useful method for balancing I/O load across an array of disks. Striping is used across disk drives in redundant array of independent disks (RAID) storage, network interface controllers, disk arrays, different computers in clustered file systems and grid-oriented storage, and RAM in some systems. Method One method of striping is done by interleaving sequential segments on storage devices in a round-robin fashion from the beginning of the data sequence. This works well for streaming data, but subsequent random accesses will require knowledge of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CAP Theorem
In theoretical computer science, the CAP theorem, also named Brewer's theorem after computer scientist Eric Brewer, states that any distributed data store can provide only two of the following three guarantees:Seth Gilbert and Nancy Lynch"Brewer's conjecture and the feasibility of consistent, available, partition-tolerant web services" ''ACM SIGACT News'', Volume 33 Issue 2 (2002), pg. 51–59. . ; Consistency: Every read receives the most recent write or an error. ; Availability: Every request receives a (non-error) response, without the guarantee that it contains the most recent write. ; Partition tolerance: The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes. When a network partition failure happens, it must be decided whether to do one of the following: * cancel the operation and thus decrease the availability but ensure consistency * proceed with the operation and thus provide availability but ri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Block Range Index
A Block Range Index or BRIN is a database indexing technique. They are intended to improve performance with extremely large tables. BRIN indexes provide similar benefits to horizontal partitioning or sharding but without needing to explicitly declare partitions. A BRIN is applicable to an index on a table that is large and where the index key value is easily sorted and evaluated with a MinMax function. BRIN were originally proposed by Alvaro Herrera of 2ndQuadrant in 2013 as 'Minmax indexes'. Implementations thus far are tightly coupled to internal implementation and storage techniques for the database tables. This makes them efficient, but limits them to particular vendors. So far PostgreSQL is the only vendor to have announced a live product with this specific feature, in PostgreSQL 9.5. Other vendors have described some similar features, including Oracle database, Oracle, Netezza 'zone maps', Infobright 'data packs', MonetDB and Apache Hive with ORC/Parquet. Design BRIN ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Columnar Database
A column-oriented DBMS or columnar DBMS is a database management system (DBMS) that stores data tables by column rather than by row. Benefits include more efficient access to data when only querying a subset of columns (by eliminating the need to read columns that are not relevant), and more options for data compression. However, they are typically less efficient for inserting new data. Practical use of a column store versus a row store differs little in the relational DBMS world. Both columnar and row databases can use traditional database query languages like SQL to load data and perform queries. Both row and columnar databases can become the backbone in a system to serve data for common extract, transform, load (ETL) and tools. Description Background A relational database management system provides data that represents a two-dimensional table of columns and rows. For example, a database might have this table: This simple table includes an employee identifier (EmpId), name ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Normalization
Database normalization or database normalisation (see spelling differences) is the process of structuring a relational database in accordance with a series of so-called normal forms in order to reduce data redundancy and improve data integrity. It was first proposed by British computer scientist Edgar F. Codd as part of his relational model. Normalization entails organizing the columns (attributes) and tables (relations) of a database to ensure that their dependencies are properly enforced by database integrity constraints. It is accomplished by applying some formal rules either by a process of ''synthesis'' (creating a new database design) or ''decomposition'' (improving an existing database design). Objectives A basic objective of the first normal form defined by Codd in 1970 was to permit data to be queried and manipulated using a "universal data sub-language" grounded in first-order logic. An example of such a language is SQL, though it is one that Codd regarded as ser ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Union (SQL)
Set operations allow the results of multiple queries to be combined into a single result set. Set operators include UNION, INTERSECT, and EXCEPT. UNION operator In SQL the UNION clause combines the results of two SQL queries into a single table of all matching rows. The two queries must result in the same number of columns and compatible data types in order to unite. Any duplicate records are automatically removed unless UNION ALL is used. UNION can be useful in data warehouse applications where tables are not perfectly normalized. A simple example would be a database having tables sales2005 and sales2006 that have identical structures but are separated because of performance considerations. A UNION query could combine results from both tables. Note that UNION ALL does not guarantee the order of rows. Rows from the second operand may appear before, after, or mixed with rows from the first operand. In situations where a specific order is desired, ORDER BY must be used. No ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
View (database)
In a database, a view is the result set of a ''stored'' query on the data, which the database users can query just as they would in a persistent database collection object. This pre-established query command is kept in the database dictionary. Unlike ordinary ''base tables'' in a relational database, a view does not form part of the physical schema: as a result set, it is a virtual table computed or collated dynamically from data in the database when access to that view is requested. Changes applied to the data in a relevant ''underlying table'' are reflected in the data shown in subsequent invocations of the view. In some NoSQL databases, views are the only way to query data. Views can provide advantages over tables: * Views can represent a subset of the data contained in a table. Consequently, a view can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base table. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Log
In the field of databases in computer science, a transaction log (also transaction journal, database log, binary log or audit trail) is a history of actions executed by a database management system used to guarantee ACID properties over crashes or hardware failures. Physically, a log is a file listing changes to the database, stored in a stable storage format. If, after a start, the database is found in an inconsistent state or not been shut down properly, the database management system reviews the database logs for uncommitted transactions and rolls back the changes made by these transactions. Additionally, all transactions that are already committed but whose changes were not yet materialized in the database are re-applied. Both are done to ensure atomicity and durability of transactions. This term is not to be confused with other, human-readable logs that a database management system usually provides. In database management systems, a journal is the record of data alt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
