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Database and Instances, Ariana Alvarado Molina - 2021089068 - Coggle…

- - - - Tablespaces
        
        A tablespace is a logical structure;
        
        Each tablespace has physical structures called datafiles.
        
        When you create a table -> you choose the tablespace.
      - Schema
        
        They correspond to an Oracle DB user.
        
        Specification: Password, tablespace, number of tablespace.
        
        They are used as a basis for multitenancy
      - Files of a database
        
        Oracle DB: Control files, Datafiles, Redo logfiles
        
        It contains information such as including: the name of the DB, when the DB was created, etc.
  - - - Oracle Database includes a single PDB in a CDB.
      - All CDBs come with a seed PDB.
      - You can move PDBs from one CDB to another.
      - You can clone an existing PDB to create a copy.
    - - Point-in-time recovery and Flashback query applicable to individual PDBs.
      - Processes such as backup, recovery and Data Guard span the entire instance.
      - In Oracle Database 12c, instances are viewed as all PDBs and the container database.
  - - - A DB must have at least two copies of the control file.
      - The location of the control files is defined as -> CONTROL_FILES.
      - parameter -> indicates where to find the control files.
    - - Data files contain -> actual data stored in the DB, tables and indexes.
      - A data file is composed of -> Oracle Database blocks -> are composed of operating system blocks on a disk.
      - The data files belong to a single database and DB tablespace.
      - Datafile structure
        
        The first block of each data file -> data file header.
        
        It contains information -> maintaining the overall integrity of DB.
  - - - Each instance uses a redo thread to log changes it makes to the DB.
      - A redo thread -> redo log groups, -> of one or more redo log members. members.
      - In redo log groups, Oracle keeps redundant copies of files.
      - Oracle must ensure that all log copies are up to date to prevent data loss.
    - - The names of files in a database are crucial for their identification by humans.
    - - First, if this is not avoided, you will lose data by overwriting the redo file.
      - The second is to archive the redo logs as they are filled.
        
        Online redo logs
        
        Archived redo logs
    - - ARCHIVE LOG START -> enable automatic archiving in Oracle
      - LOG_ARCHIVE_START = TRUE
      - LOG START activates automatic archiving and the archives are started.
  - - - The database cache stores blocks of data extracted from the database.
      - Oracle uses the LRU algorithm to manage this cache.
      - User reads non-cached block -> loads from disk to cache.
      - Changes are written to disk afterwards, avoiding delays to users.
    - - The PL/SQL functions are loaded into the shared pool.
      - In Oracle Database 11g, -> PL/SQL so that its result is cached.
      - Configure SHARED_POOL_SIZE -> manually
      - Oracle Database 10g, a Shared Pool could cause "out of memory" errors.
    - - The redo log buffer caches redo before writing it to physical files on disk.
      - This buffer also improves performance.
  - - - Checkpoint
        
        Updates datafile headers whenever a checkpoint is performed.
      - Log Writer
        
        Writes the redo information from the log buffer in the SGA to all copies of the
        current redo logfile on disk.
      - Database Writer
        
        Writes database blocks from the database buffer cache in the SGA to the datafiles
        on disk
      - Porcess Monitor
        
        PMON monitors and clears resources in case of abnormal termination of user processes in the database.
      - Archiver
        
        Oracle reads and writes copies of redo log files to specific destinations once they have been populated.
      - Recover
        
        Automatically cleans up failed or suspended distributed transactions.
      - Queue Monitor
        
        Monitors Oracle Streams message queues with up to 10 monitoring processes
        supported.