openGauss Glossary II
Published: 2023-02-22 02:18:21

F – J

failover

Automatic switchover from a faulty primary node to its standby node. Reversely, automatic switchback from the standby node to the primary node is called failback.

FDW

Acronym for foreign data wrapper. It is an SQL interface provided by openGauss. It is used to access big data objects stored in remote data so that DBAs can integrate data from unrelated data sources and store them in public schema in the database.

freeze

An operation automatically performed by the AutoVacuum Worker process when transaction IDs are exhausted. openGauss records transaction IDs in the row heading. When a transaction reads a row, the transaction ID in the row heading and the actual transaction ID are compared to determine whether this row is explicit. Transaction IDs are integers containing no symbols. If exhausted, transaction IDs are re-calculated outside of the integer range, causing the explicit rows to become implicit. To prevent such a problem, the freeze operation marks a transaction ID as a special ID. Rows marked with these special transaction IDs are explicit to all transactions.

GDB

Acronym for GNU debugger which is used to monitor the internal situation of a running program or rewind a crashed program to see what happened. GDB can perform the following operations (strengthening PDK functions) to detect bugs:

Starts a program and specifies anything that might affect its behavior.
Stops a program under a specific condition.
Checks what happens when a program stops.
Modifies the program content to rectify the fault and proceeds with the next one.
GIN index

Acronym for generalized inverted index. It is used for handling cases where the items to be indexed are composite values, and the queries to be handled by the index need to search for element values that appear within the composite items.

GNU

The GNU Project was publicly announced on September 27, 1983 by Richard Stallman, aiming at building an OS composed wholly of free software. GNU is a recursive acronym for "GNU's Not Unix!". Stallman announced that GNU should be pronounced as Guh-NOO. Unix is a widely used commercial OS. GNU's design is Unix-like, but GNU differs from Unix by being free software.

Shared storage

Shared storage enables the primary and standby nodes to share the same storage. In traditional HA deployment mode, the storage capacity is doubled compared with that of a single node. This feature provides a new HA deployment mode for the primary/standby shared storage, meeting the requirements for reducing the storage capacity and costs. Log replication is not required between the primary and standby nodes. Instead, page exchange is implemented between the primary and standby nodes and real-time read consistency is supported on the standby node.

gsql

openGauss interaction terminal. It enables you to interactively enter and issue queries to openGauss, and view the query results. Queries can also be entered from files. In addition, gsql supports many meta commands and shell-like commands, allowing you to conveniently compile scripts and automate tasks.

GUC

Acronym for grand unified configuration which includes parameters for running databases, and the values of which affect database system behavior.

HA

Acronym for high availability which helps to minimize the duration of service interruptions caused by routine maintenance (planned) or sudden system breakdowns (unplanned), improving the system and application usability.

HBA

Acronym for host-based authentication which allows hosts to authenticate on behalf of all or some of that particular host's users. Those accounts can be all of the accounts on a system or a subset designated by the Match directive. This type of authentication can be useful for managing computing and other fairly homogenous pools of machines. In all, three files on the server and one file on the client must be modified to prepare for host-based authentication.

IV

Acronym for initialization vector. An IV is a block used for random encryption in many encryption modes. Therefore, different ciphertexts may be generated by using the same plaintext and key.

server

A combination of hardware and software designed for providing clients with services. This word alone refers to a computer running a server OS, or software or dedicated hardware providing services.

isolation

One of the ACID properties of a database transaction. Isolation means that operations and data used in a transaction are isolated from those in other concurrent transactions. Concurrent transactions are independent of each other.

relational database

A database that conforms to the relational model. It processes data using mathematical concepts and methods such as the set algebra.

archive thread

A thread started when the archive function is enabled on a database. The thread is used to archive database logs to a specified path.

failover

Automatic substitution of a functionally equivalent system component for a failed one. The system component can be a processor, server, network, or database.

environment variable

Environment variables are used to define part of the environment in which a process runs. For example, it can be used to define a home directory, command search path, terminal being used, or the current time zone.

checkpoint

A mechanism that stores data at a certain time in the database memory to disks. openGauss 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.

encryption

A function hiding information content during data transmission to prevent the unauthorized use of the information.

node

Database nodes (or nodes) are physical and virtual severs that make up the openGauss database environment.

error correction

A technique that automatically detects and corrects errors in software and data flows to improve system stability and reliability.

process

An instance of a computer program that is being executed. A process consists of one or more threads. A process cannot use a thread occupied by another process.

PITR

Acronym for point-in-time recovery, a backup and restoration feature of openGauss. Data can be restored to a specified point in time if backup data and WAL logs are normal.

record

In a relational database, a record corresponds to data in each row of a table.