openGauss IV
Published: 2023-02-22 02:20:10

P – T

page

Smallest memory unit for row storage in the relational object structure in openGauss. The default size of a page is 8 KB.

Paxos

Distributed consistency protocol.

PostgreSQL

An open-source relational DBMS developed by volunteers all over the world. PostgreSQL is not controlled by any companies or individuals. Its source code can be used for free.

postmaster

A thread started when the database service is started. It listens on connection requests from other nodes in the database or from clients.

After receiving and accepting a connection request from the standby node, the primary node creates a WAL sender thread to interact with the standby node.

RHEL

Acronym for Red Hat Enterprise Linux.

redo log

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.

RK

Acronym for root key.

SCTP

Acronym for stream control transmission protocol. It is a transport-layer protocol defined by Internet Engineering Task Force (IETF) in 2000. The protocol ensures the reliability of datagram transport based on unreliable service transmission protocols by transferring SCN narrowband signaling over IP network.

savepoint

A savepoint marks the end of a sub-transaction (also known as a nested transaction) in a relational DBMS. The process of a long transaction can be divided into several parts. After a part is successfully executed, a savepoint will be created. If later execution fails, the transaction will be rolled back to the savepoint instead of being totally rolled back. This is helpful for recovering database applications from complicated errors. If an error occurs in a multi-statement transaction, the application can be restored by rolling back to the savepoint without terminating the entire transaction.

session

If a database receives a connection request from an application, a task is created for the connection. Sessions are managed by the session manager. They execute initial tasks and perform all user operations.

SMP

Acronym for symmetric multiprocessing. A group of processors (multiple CPUs) is integrated on a computer. These CPUs share the memory subsystem and bus structure. The OS must support multitasking and multithreading to ensure an SMP system achieves high performance. In databases, SMP means to concurrently execute queries using the multi-thread technology, efficiently using all CPU resources and improving query performance.

SQL

Acronym for structured query language. A standard database query language, consisting of data definition language (DDL), data manipulation language (DML), and data control language (DCL).

SSL

Acronym for secure sockets layer. It is a network security protocol introduced by Netscape. It is based on the TCP/IP and uses public key technology. SSL supports a wide range of networks and provides three basic security services, all of which use the public key technology. SSL ensures the security of service communication through the network by establishing a secure connection between a client and a server and then being able to securely send any data through this connection.

oversubscription ratio

The ratio of downlink bandwidth to uplink bandwidth of a switch. A high oversubscription ratio indicates a highly oversubscribed traffic environment and severe packet loss.

Table Access Method

The table access method layer decouples the execution engine from the storage engine to implement the pluggable capability of the storage engine.

TCP

Acronym for transmission control protocol. It splits data into packets which are sent through the Internet protocol (IP), and checks and reassembles packets received through IP to obtain original information. TCP is a connection-oriented, reliable protocol that ensures information correctness in transmission.

trace

A specialized use of logging to record information about the way a program is executed. Programmers use the information for debugging. System administrators and technical support personnel can diagnose common problems by using software monitoring tools and based on this information.

strong consistency

A query cannot see any instantaneous intermediate state of a transaction.

full backup

Backup of the whole database.

full synchronization

A data synchronization mechanism specified in the openGauss primary/standby solution, which is used to synchronize all data from the primary node to a standby node.

log file

A file containing a record of to activities made in a computer.

transaction

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.

data

A representation of facts or directives for manual or automatic communication, explanation, or processing. Data includes constants, variables, arrays, and strings.

data partition

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.

database

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.

database instance

A database instance consists of a process in openGauss and files controlled by the process. openGauss allows multiple database instances to be installed on one physical node. A database instance is also called a logical node.

database primary/standby solution

openGauss provides a highly reliable HA solution. In this solution, each openGauss is called a primary or standby node. At the same time, only one openGauss is identified as the primary node. When the primary/standby system is deployed for the first time, the primary node performs full synchronization on the standby node, and then performs incremental synchronization on the standby node. When the primary/standby system is running, the primary node can receive data read and write operation requests and the standby node only synchronize logs.

database file

A binary file that stores user data and the data inside the database system.

data dictionary

A read-only collection of database tables and views containing reference information about the database. The information includes database design information, stored procedure information, user rights, user statistics, database process information, database increase statistics, and database performance statistics.

deadlock

A situation where different transactions are unable to proceed, because each holds a lock that the other needs.

index

An ordered data structure in DBMS to help quickly query and update data in database tables.

statistics

Information that is automatically collected by databases, including table-level information (number of tuples and number of pages) and column-level information (column value range distribution histogram). Statistics in databases are used to estimate the cost of query plans to find a plan with the lowest cost.

stop word

In computing, stop words are words which are filtered out before or after processing of natural language data (text), saving storage space and improving search efficiency.