Oracle database Physical structure Logical structure memory chunk process management

Oracle as a huge system, how to understand its structure, it must be layered.

The so-called physical structure, is stored in the operating system files, including control files, data files, redo log files, other (initialization parameter files, follow-up files, warning files, backup files, password files).

Logical structure, is the programmer's brain in the division of the database, it is not real existence, but a concept, and physical structure has a certain correspondence, not one by one correspondence. It contains table spaces, logical objects (tables, indexes, views), segments (data segments, index segments, temporary segments, regression segments), extents, and blocks. The segment and data file is a two-dimensional table relationship, in the same table space, that is, a segment can be stored in multiple data files, a data file can contain multiple segments. Area and block of words on the finer particles, generally from the bottom of the transparent implementation, temporarily do not explore.

Memory chunks and process management, that is, Oracle startup is the only thing, put them together to see. When a set of Oralce starts, there will be three service processes, including the instance process, the listener process, and the Enterprise Manager service (a Web service). When a user requests, the listener process assigns a server process, the server process has a PGA (program global, contains the sort area, the session area, the cursor area, the stack area). Server processes and PGA are not directly associated with database files, there is a background process (including process monitoring process pmon, system monitoring process Smon, database write process DBWR, log file write process LGWR, checkpoint process ckpt, etc.) and SGA (System global Zone, Contains data to tell buffers, redo log buffers, shared pools, etc.).

A big thing consists of a lot of content, how to name a lot of creators of the likes, just know that there is such a thing, what it does, do not need to tangle what it is.

Oracle database Physical structure Logical structure memory chunk process management