Oracle-related Fundamentals

Oracle- related Fundamentals relational database and non-relational database

Relational database is a database based on the relational model, and the relational model is a two-dimensional table to represent and store the data;

non-relational database (NoSQL) is a key-value pair that stores data in a way that Key-value . Redis

Database and instance

A database is a heap of files, a physical concept; a bunch of files inside a database file are loaded into memory, and the image in memory is called an instance, and the instance is a logical concept;

Operation of the database requires an action instance.

Oracle 's cluster

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Oracle 's architecture

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Any language operates on the database file as a process of the operating system.

in the diagram, the client (such as jdbc) connects to the database, and the small squares in the general diagram are the same as the number of connections; an instance has only one large square.

the generous blocks are: SGA ( system Global Area Systems Globals )

small squares are: PGA (Process Global area)

client operation data, saved in PGA , commit commits after operation,PGA writes to SGA,SGA Writes a database file through a write process. This is done by committing the data in two phases and writing faster. Because if the PGA is written directly to the database, then three PGA will need to write three times, if submitted to the SGA only need to write once.

This article is from the "QB blog" blog, declined reprint!

Oracle-related Fundamentals