Beginning with oracle database 11 g, oracle database can manage the sga memory and instance pga memory completely automatically. How to check if my oracle sga is undersized or oversized. If the advisor came back and said increase buffer cache by x% and you will decrease physical io by y%, that would be the differentiator. Asmm amm and dynamic memory management has measurable overhead. Sga system global area is an area of memory ram allocated when an oracle instance starts up. Should both parameters be set to the same value initially and if not, why. The oracle dba can use math to determine the optimal ram allocation for a mswindows server. Oracle 11g takes this one step further by allowing you to allocate one chunk of memory, which oracle uses to dynamically. So, in dedicated server mode, when session migration is not needed, the uga is in the pga is in the individual. Changing the sga andor pga in oracle 11g affects the performance of the queries. That will control the sizing of the sga and pga the max targets will be reserved, but the in use amount would dynamically change for both sga and pga as the workload changes. How to determine if it is necessary to increase the sga and the pga in oracle database.
Oracle white paper dynamic sga tuning of oracle database on oracle solaris with dism 3 other benefits of ism since ism memory is locked, no swap space is needed to back it, thereby saving disk space. The pga is a memory heap that contains sessiondependent variables required by a dedicated or shared server process. A system privelege is introduced in 11g called sysasm, and this is granted to users who need to perform asm related tasks. Well i shall share the example that i give when i talk about the same.
The server process allocates memory structures that it requires in the pga. If manual shared memory management is currently enabled, but you would like oracle database to help you determine optimal sizes of the sga and instance pga, you can disable manual shared memory management and enable automatic shared memory management. A sort job that oracle performs entirely in memory is said to be an optimal sort. Oracle 10g to 11g enhancements difference between oracle 10g and 11g oracle dba irfan khanoctober 16, 2017 0. Oracle asmm and amm are not the same and are associated.
Assume that there are 10 people sitting and listening to you in a class. The sga is a group of shared memory structures, known as sga components, that contain data and control information for one oracle database instance. The system global area sga is a shared memory region that contains data and control information for one oracle instance. In 9i, the sga is the sga it is all owned by oracle, you set the sizes of the individual components but it is pretty much the size it is. Difference between oracle 10g and 11g simplified and. Examples of data stored in the sga include cached data blocks and shared sql areas. How to perform rman cloning easy process to clone a database on different server. A pga is created by oracle database when an oracle process is started. A system global area is a group of shared memory areas that dedicated to an oracle database instance. The total ram sga and pga estimates for oracle are as follows. On first blush, that strikes me as rather low unless you have a particularly large pga, you have other things consuming memory on the server, or you have reason to believe that file system caching is going to be more effective than having the ram allocated to oracle. How to isolate general oracle 10g issues through sql.
For the purposes of this example, lets assume that we are on a dedicated mswindows oracle server, and oracle will be the only program running on the server. Oracle database architecture is a combination of instance and database. The shared pool pga it stands for program global area. In this article, we will discuss how to get monitor free memory in system global area sga in oracle 10g. Scope and application dbas with prior knowledge of 9i and 10g memory management. Estimating sga size tips oracle consulting, oracle. System global area sga is is a group of shared memory areas that are dedicated to an oracle instance program global area pga. Oracle asmm and amm are not the same and are associated with different releases of oracle.
The sga is shared by all server and background processes. In manual pga memory management, the parameters that have the largest. You designate only the total memory size to be used by the instance, and oracle database dynamically exchanges memory between the sga and the instance pga as needed to meet processing demands. Its session state information, plsql package variables, and other stuff that must always be available to the session. However, it is possible for the pga allocated to exceed that value by a small percentage and for a short period of. See these important notes scripts for detecting amm resize operations. In general, oracle would prefer to keep stuff in the pga, rather than sga, since the pga is private, and no latching is required for accessing any pga. Base tables are dictionary information of the database. What is the difference bitween sga and pga memory in oracle. Enabling automatic shared memory management oracle. The system global area sga memory structures in data.
Program global areas pga, which is private to each server and background process. It would all be in use in oracle10g and above, the sga has a target. Program global area pga a pga is a nonshared memory region that contains data and control information exclusively for use by an oracle process. Oracle 10g to 11g enhancements difference between oracle. However, to allow oracle to take full control of the memory management, these parameters should be set to zero. Table 141 differences in memory allocation between dedicated and shared servers. The definition of a small table is the maximum of 2% of the buffer cache and 20. Oracle dba tutorial for beginners and professionals. Oracle 11g takes this one step further by allowing you to allocate one chunk of memory, which oracle uses to.
To be precise about the oracle 10g, 10g is oracle s network calculating product group counting among other things a database management system dbms and. Specifically, memory for collections is stored in the program global area pga, not the system global area sga thus, if a program requires 5mb of memory to populate a collection and there are 100 simultaneous connections, that program causes the consumption of 500mb of pga memory, in addition to the memory allocated to the sga. With manual configuration of the sga, it is possible that compiled sql. The process global area pga is memory which is physically private to a process cannot be accessed by another process. From oracle 10g, the spool command can append to an existing one. In oracle database 10g, a dba can simply specify the total amount of sga. Ism memory can also be locked by the oracle user without the need for superuser privileges, thereby simplifying system administration. For example, the dynamic memory allocation features of oracle make it possible to create a selftuning oracle sga. Oracle dba interview questions and answers discussion the basic difference between sga and pga is that pga cannot be shared between multiple processes, in the sense, that it is used only for requirements of a particular process whereas the sga is used for the whole instance and it is shared.
Sga is allocated whenever an oracle instance starts and gets deallocated when the oracle instance is shutdown. The program global area, or pga, is part of the memory allocated to a 12c instance as it is started. Oracle database concepts for information on automatic sga management. Tools and methods of databases optimization in oracle database.
Oracle introduces amm feature from 11g which will manage sga as well as pga. The basic difference between sga and pga is that pga cannot be shared between multiple processes, in the sense, that it is used only for requirements of a particular process whereas the sga is used for the whole instance and it is shared. Sga memory management is enabled, the sizes of the different sga components. See my notes on the difference between asmm and amm. There is an advisory on using bitmap free lists asmm.
Os ram 20 percent of total ram for mswindows, 10% of ram for unix. So, to clear all your confusions on interview locations, interview questions we have given detail on our wisdomjobs site. Sga and pga are parts of the memory architecture of oracle database. For example, 20 executions of select from employees in one session and 10 executions of the same query in a different. Because the pga is processspecific, it is never allocated in the sga. Understanding oracle database sga and pga oracle memory.
Users currently connected to an oracle database share the data in the sga. The sgas size and function are controlled by initialization init. How to find out check sga and pga size of oracle database. In oracle, we see more selftuning capability than ever before, and it is even easier to write detection scripts and schedule tasks to adjust oracle based on processing needs. The following oracle database views provide information about the sga components and their dynamic resizing. Oracle allocates the sga when an instance starts and deallocates it when the instance shuts down.
One pga exists for each server process and background process. Changing the sga andor pga in oracle 11g affects the. Note that an os process and an oracle session are not equivalent. In other words, there is no other application on it. If automatic memory management is currently enabled, but you would like to have more direct control over the sizes of the system global area sga and instance program global area pga, you can disable automatic memory management and enable automatic shared memory management. The pga is memory specific to an operating process or thread that is not shared by other processes or threads on the system. Unlike the memory in the sga, pga memory is not shared.
Oracle database creates the pga when an oracle process starts. For example, 20 executions of select from sales in one session and 10 executions of the same query in a different session. Instance is a combination of memory structures and background processes which helps in reading and writing the data tofrom the database. What is the difference between projection and selection. Dynamic sga tuning of oracle database on oracle solaris.