A mechanism that stores data from the database memory to disks at a certain time. The database periodically stores the data of committed transactions and data of uncommitted transactions to disks. The data and redo logs can be used for database restoration if a database restarts or breaks down.
The smallest management unit in DWS. A cluster represents a separately running data warehouse. Users can manage the lifecycle of a cluster in DWS.
An equivalent concept of field. A database table consists of one or more columns.
Compression Unit (CU) is the smallest storage unit in a column-storage table.
A DBMS service that ensures data integrity when multiple transactions are concurrently executed in a multi-user environment. In a multi-threaded DWS environment, concurrency control ensures that database operations are safe and all database transactions remain consistent at any given time.
See Compression Unit
A subset of SQL for setting or modifying database user or role rights.
A subset of SQL for defining data structures and database objects.
A reserved table within a database which is used to store information about the database itself. The information includes database design information, stored procedure information, user rights, user statistics, database process information, database increase statistics, and database performance statistics.
A subset of SQL for accessing data for database objects.
The action of dividing a table into parts (partitions) whose data does not overlap within a database instance. Tables can be partitioned by range, where the target storage location is mapped based on the range of the values in the column that is specified in the tuple.
Data Warehouse Service is an online data processing database based on the public cloud infrastructure and platform and helps you mine and analyze massive sets of data.
A collection of data that is stored together and can be accessed, managed, and updated. Data in a view in the database can be classified into the following types: numerals, full text, digits, and images.
A process and the database files that it controls. The cluster installs multiple database instances on one physical node. The GTM, CM, CN, and DN installed on cluster nodes are all database instances. A database instance is also called a logical node.
A process of data transmission from the source to the target database.
Massive Parallel Processing (MPP) refers to cluster architecture that consists of multiple machines. The architecture is also called a cluster system.
Data that provides information about other data. Metadata describes the source, size, format, or other characteristics of data. In the data field, metadata helps to explain the content of a data warehouse.
Online analytical processing (OLAP) is the most important application in the database warehouse system. It is dedicated to complex analytical operations, helps decision makers and executives to make decisions, and rapidly and flexibly processes complex queries involving a great amount of data based on analysts' requirements. In addition, the OLAP provides decision makers with query results that are easy to understand, allowing them to learn the operating status of the enterprise. These decision makers can then produce informed and accurate solutions based on the query results.
When a data warehouse enters read-only state, it responds only to reads. The warehouse becomes read-only in many situations, for example, when you create a cluster snapshot or when 90% of the cluster's storage capacity is used.
A log that records operations on the database. Redo logs contain the information required for performing these operations again. If a database is faulty, redo logs can be used to restore the database to its pre-fault state.
A database object set that includes the logical structure, such as tables, views, sequences, stored procedures, synonyms, indexes, clusters, and database links.
A segment in the database indicates a part containing one or more regions. Region is the smallest range of a database and consists of data blocks. One or more segments comprise a tablespace.
A distributed computing architecture, in which none of the nodes share a CPU or storage resources. This architecture has good scalability.
A full backup of a cluster. Snapshots are stored in the storage space of Object Storage Service (OBS).
A snapshot can be used to restore a cluster to a newly created one that has the same specifications. Currently, you can restore a cluster only to a new one.
Information that is automatically collected by databases, including table-level information (number of tuples and number of pages) and column-level information (distribution histograms of value ranges of columns). Statistics in databases are used to estimate the cost of query plans to find the plan with the lowest cost.
A group of SQL statements compiled to perform certain functions and stored in a large database system. Users can specify a name and parameters (if any) for a stored procedure to execute the procedure.
Structure Query Language (SQL) is a standard database query language. It consists of DDL, DML, and DCL.
A table storing meta information about the database. The meta information includes user tables, indexes, columns, functions, and data types in a database.
A set of columns and rows. The value in each column represents data of a certain type. For example, if a table contains people's names, cities, and states, it has three columns: Name, City, and State. In every row in the table, the Name column contains a name, the City column contains a city, and the State column contains a state.
A tablespace is a logical storage structure that contains tables, indexes, large objects, and long data. A tablespace provides an abstract layer between physical data and logical data, and provides storage space for all database objects. When you create a table, you can specify which tablespace it belongs to.
A logical unit of work performed within a database management system against a database. A transaction consists of a limited database operation sequence, and must have ACID features.
Write-ahead logging (WAL) is a standard method for logging a transaction. Corresponding logs must be written into a permanent device before a data file (carrier for a table and index) is modified.
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