System Global Area

System Global Area

System Global Area (SGA) nennt man die prozessübergreifenden Speicherbereiche im Hauptspeicher des Datenbankservers einer Oracle Datenbank. Dort liegen alle notwendigen Daten für die Instanz-Operationen.

In diesem Speicherbereich befindet sich

  • Buffer Cache: Hier werden Datenblöcke zwischengespeichert, die von der Platte gelesen werden. Dies ermöglicht es, beim mehrmaligen Zugriff auf Datenblöcke diese aus dem Cache zu lesen, anstatt diese jeweils erneut von der Platte zu lesen.
  • Dictionary Cache: Er enthält Informationen über Data Dictionary-Tabellen, dazu gehören Informationen über Benutzerkonten , Datenbankdateien, Segmente, Extents, Tabellen und Rechte (privileges).
  • Redo Log Buffer: Er enthält Informationen über abgeschlossene Transaktionen, die noch nicht in die Online Redo Log Dateien geschrieben wurden.
  • Shared Pool: Hier werden u.a. die zuletzt benutzten SQL-Befehle und ihre Ausführungspläne sowie der Dictionary Cache (s.o.) gespeichert.
  • JAVA Pool (optional): Zur Analyse der Java-Befehle.

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