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.

参考以下模块类型:

• 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
  共享池中的MCODE子堆

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.
该layer管理特定会话非共享的资源,如实例化的包含了包全局变量状态信息的PL/SQL程序单元

KOH/KGH 该layer用以管理heap service堆服务

PLSQL MCODE Heap的属性

• 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.