- oracle---latest version---10i
- developed by larry allison
- its a RDBMS-Relational Database Management System
- every oracle database consists of an instance and some storage associated to that instance...instance has some processes and memory structures associated to it........2 main processes are SMON (System Monitor) and PMON (Process Monitor)
- oracle has 2 levels of storage: physical and logical
- physical space contains actual files and logical space consists of tablespaces
- tablespaces consists of segments....segments can be data segments, index segments, etc.
- segments consists of extents...which further consists of data blocks which are smallest units of storage
- actual physical data files consists of these data blocks
- one inbuilt tablespace is SYSTEM which contains data dictionary(this dictionary contains information abt all database objects)
- then next comes SCHEMAS used to differentiate user groups...one default schema is there with username: scott and Password: tiger
- you can also create your schemas
- next comes storage architecture.......either SGA or PGA
- SGA-system/shared global area 3 things are there in this: data cache buffer, redo log cache buffer and shared pool
- data cache contains most recently seen data blocks, dirty blocks(modified blocks nt written on disk), clean blocks(written to disk)
- redo log cache buffer is used to store transactions and is used for recovery purposes.
- shared pool consists of library cache and data dictionary cache
- library cache consists of various SQL execution paths..and if same query is executed by multiple applications then the same shared pool is used
- data dictionary cache consisits of user info, integrity constraints, etc.
- there shud be enuf memory allocted to shared pool, otherwise users may see degradation in performance
- PGA-Program Global Area maintains and controls oracle server
PS: this information is nt guaranteed to be correct..
n i will b glad if u ppl add more to this
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