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This article mainly introduces "what is the memory structure of Oracle database". In daily operation, I believe that many people have doubts about the memory structure of Oracle database. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "what is the memory structure of Oracle database?" Next, please follow the editor to study!

Each database instance has two associated memory structures-the system global area (SGA) and the program global area (PGA).

System global (SGA): a set of shared memory structures (called SGA components) that contain data and control information for an OracleDB instance. SGA is shared by all server processes and background processes. The data stored in SGA includes cached data blocks and shared SQL areas, etc. The size of SGA is determined by the parameter sga_target.

Program global area (PGA): the area of memory that contains data and control information about a server process or background process. PGA is the unshared memory that Oracle DB creates when a server process or background process starts. Server processes have exclusive access to PGA. Each server process and background process has its own PGA. The size of the PGA is determined by the parameter pga_aggregate_target.

Several key components of SGA are used to illustrate:

Shared pool: shared pool, used to cache various constructs that can be shared among users, such as the parse tree and execution plan of a given SQL statement.

Database buffer cache: buffer cache, the data blocks retrieved from the database are cached here, and the data blocks are operated on the data blocks from this memory component, reducing the IO burden of the hard disk. If the data needed by the user process can be found in this area, we call it a cache hit. The high hit rate reflects the effect of fast operation response, which is easy to understand. It is necessary to consider this in database optimization.

In buffer cache, the following buffers exist:

(*) KEEP buffer pool: a dedicated database buffer cache used to keep blocks in memory for long periods of time. Some frequently used data blocks can be retained here for a relatively long time, so that they can not be obtained from the hard disk every time, thus optimizing the performance of the database.

(*) RECYCLE buffer pool: a dedicated database buffer cache that is used to quickly reclaim or delete blocks from memory. Relative to the opposite of KEEP, it is easy to understand.

(*) nK buffer cache: one of several dedicated database buffer caches used to hold blocks of data that are different in size from the default database block size. Note that the default data block is 8K

Redo log buffer: log buffer, used to hold information about changes made to the database, where redo information is cached before being written to the redo log file (that is, redo file) on disk.

A large pool used to provide large memory allocations for some large processes, such as Oracle backup and restore operations, and Imax O server processes.

Java pool and stream pool

At this point, the study on "what is the memory structure of Oracle database" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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