PL/SQL Virtual Machine Memory Usage

PL/SQL Program Units即PL/SQL程序单元,常被叫做”library units”或lib-units.


  • package spec
  • package body
  • top-level function or procedure
  • type spec
  • type body
  • trigger
  • anonymous blocks.

PL/SQL 虚拟机的内存使用主要体现在4个方面:

  • PGA
    • PL/SQL stack call,用于保存本地变量和其他一些状态结构
    • NCOMP生成的动态链接库文件
  • CGA
    • 二级内存(secondary memory),分配的堆和大的可收缩本地变量如大的strings、Lob或collections
  • UGA
    • 程度单元的实例(library-unit instantiations),如package global variables, DL0/ DL1 dependency vectors, display frame等
  • SGA

KGL – Kernel Generic Library Manager
该layer管理会话间需要共享的资源,如PL/SQL MCODE,Diana,Source,SQL cursor,SQL Plan)

KGI – Kernel Generic Instantiation Layer.

KOH/KGH 该layer用以管理heap service堆服务




  • machine dependent binary format for a compiled PL/SQL library-unit.
  • to execute code in a lib-unit, its MCODE heap must be loaded in memory.
  • MCODE is loaded in SGA and is “pinned” for CALL duration.
  • once unpinned, the heap may be aged; hence, may need to get re-loaded.
  • important to page large data structures in SGA.

MCODE Heap: Subcomponents

  • EntryPoint Piece (PL_UEP)
  • Code Segment or Byte Code Piece (PL_UCP)
  • Constant Pool:
    • Data Segment (PL_UKP)
    • Handle Segment (PL_UHS)
  • SQL Strings Table (PL_USP)

PL/SQL Instantiations

  • When a lib-unit is first referenced by a program (session) an instantiation of the lib unit is created.
  • PL/SQL relies on KGI for inst obj mgmt.
  • A PL/SQL lib-unit instantiation consists of:
    • PLIO struct (the handle of the PL/SQL inst obj)
    • Static Frame
    • Secondary (Heap) Memory for package globals
  • PLIO Struct
    • first portion of PLIO struct is the KGIOB struct (kgi’s portion of the object handle)
    • points to the static frame struct (PLIOST)
    • also contains other book-keeping info (such as memory duration of instantiation’s work area, etc.)
  • Static Frame:
    • represents that part of instantiation’s work area whose size is compile-time determined.
    • the root of the static frame is PLIOST struct which leads the following sub-pieces:
      • depends-on array to global variable vectors (DL0)
      • depends-on array to other instantiations (DL1)
      • Display Frame (DPF)
      • global variable vector for this unit (GF)
      • primary memory for global variables.
  • Secondary Memory for package globals
    • used to allocate data types that are stored out-of-line (heap allocated) e.g., collections, large strings, large records, LOBs, datetime types, etc.

Structure of a PLSQL Instantiation Object
Memory Model In PLSQL Instantiation




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