What are the memory structures that must be managed in Oracle?
The memory structures that must be managed are the system global area (SGA) and the instance program global area (instance PGA). Oracle Database supports various memory management methods, which are chosen by initialization parameter settings. Oracle Database can manage the SGA memory and instance PGA memory completely automatically.
What is automatic memory management in Oracle Database?
Oracle Database can manage the SGA memory and instance PGA memory completely automatically. 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. This capability is referred to as automatic memory management.
How do I manage instance memory in Oracle Database?
You can allow the Oracle Database instance to automatically manage and tune memory for you. The simplest way to manage instance memory is to allow the Oracle Database instance to automatically manage and tune it for you.
Can I manually manage memory in a database?
If you prefer to exercise more direct control over the sizes of individual memory components, you can disable automatic memory management and configure the database for manual memory management. There are a few different methods available for manual memory management. Some of these methods retain some degree of automation.
What is Oracle memory structure?
The basic memory structures associated with Oracle Database include: System global area (SGA) The SGA is a group of shared memory structures, known as SGA components, that contain data and control information for one Oracle Database instance. All server and background processes share the SGA.
What is automatic memory management in Oracle?
With automatic memory management, the Oracle instance dynamically tunes all memory components to optimize performance as the workload changes. To enable automatic memory management: Start SQL*Plus and connect to the database as SYSDBA .
What is difference between SGA and PGA?
There is no ratio between the two. The SGA is sized according to how much code and data is getting sent to the server, and the PGA is dynamic according to how many processes are active.
How do I reduce the memory usage in Oracle?
ALTER SYSTEM SET pga_aggregate_target = 8289 M; ALTER SYSTEM SET sga_target = 1536 M; I had restarted the oracle service....Execute from sqlplus show parameter target . ... I had executed. ... Updating ALTER SYSTEM SET memory_max_target = 10334765056 SCOPE=SPFILE; gives me the solution.More items...•
What is DB cache size in Oracle?
DB_CACHE_SIZE specifies the size of the DEFAULT buffer pool for buffers with the primary block size (the block size defined by the DB_BLOCK_SIZE initialization parameter). The value must be at least 4M * number of cpus * granule size (smaller values are automatically rounded up to this value).
How do I test my SGA?
Check the Usage of SGA in OracleCheck the Usage of SGA. select round(used.bytes /1024/1024 ,2) used_mb. ... Find the Total Size of SGA. SELECT sum(value)/1024/1024 "TOTAL SGA (MB)" FROM v$sga; ... Check size of different pool in SGA.
What is SGA size?
The granule size depends on the database version and sometimes on the operating system. In Oracle 9i and earlier, it is 4 MB if the SGA size is less than 128 MB, and 16 MB otherwise. For later releases, it is typically 4 MB if the SGA size is less than 1 GB, and 16 MB otherwise.
What is dirty buffer in Oracle?
A dirty buffer is a buffer whose contents have been modified. Dirty buffers are freed for reuse when DBWR has written the blocks to disk. The database buffer cache is organized in two lists: the write list and the least-recently-used (LRU) list.
Why PGA is used in Oracle?
The PGA is used to process SQL statements and to hold logon and other session information. A large part of the PGA is dedicated to SQL work areas, which are working memory areas for sorts and other SQL operations.
How do I allocate more memory to Oracle?
You add physical memory to the computer running Oracle Database XE and want to allocate more to the database. In this case, increase both the SGA and PGA Aggregate sizes, maintaining roughly the original ratio of SGA size to PGA Aggregate size. You receive an error due to insufficient memory.
How can I improve my SGA?
Connect to the database sysdba sqlplus sys/oracle@op as sysdba 2. Increase sga_max_size to 6 GB as below SQL> ALTER SYSTEM SET sga_max_size=6144m scope=spfile; System altered. 3. Increase pga_aggregate_targe to 3 GB as below SQL> ALTER SYSTEM SET pga_aggregate_target= 3072MB SCOPE=spfile; 4.
What are memory parameters?
Memory parameters are initialization parameters that determine the total size of the system global area (SGA) and the program global area (PGA), and of the subcomponents of the SGA. The settings of memory parameters can affect the performance of your database.
What is automatic memory management?
Automatic memory management can eliminate common problems, such as forgetting to free an object and causing a memory leak, or attempting to access memory for an object that has already been freed. This section describes how the garbage collector allocates and releases memory.
What is an automatic memory manager?
Automatic memory management (AMM) is a technique in which an operating system or application automatically manages the allocation and deallocation of memory. This means that a programmer does not have to write code to perform memory management tasks when developing an application.
What is the difference between ASMM and AMM?
I understand that the difference between ASMM and AMM depends on the release of Oracle. Answer: Yes, Oracle ASMM and Oracle AMM are for different releases of Oracle: AMM in Oracle 11g: The 11g release uses AMM and manages all of the SGA AND PGA via the memory_target parameter. Also, AMM does not use Linux hugepages.
What is difference between SGA_Target and memory_target Oracle?
SGA_Target is the size of the SGA not including the PGA. Memory_Target includes both. If the PGA_target + SGA_Target are > Memory_Target, you can get this error.
How to manage Oracle instance memory?
To do so (on most platforms), you set only a target memory size initialization parameter ( MEMORY_TARGET) and optionally a maximum memory size initialization parameter ( MEMORY_MAX_TARGET ).
Which memory structure must be managed?
The memory structures that must be managed are the system global area (SGA) and the instance program global area (instance PGA). Oracle Database supports various memory management methods, which are chosen by initialization parameter settings.
How to control PGA memory?
You can control this amount by setting the initialization parameter PGA_AGGREGATE_TARGET.
What is SGA_TARGET in Oracle?
With automatic shared memory management, you specify the total amount of SGA memory available to an instance using the SGA_TARGET initialization parameter and Oracle Database automatically distributes this memory among the various SGA components to ensure the most effective memory utilization.
Why does Oracle not cache?
In default caching mode, Oracle Database does not always cache the underlying data when a user queries a large table because doing so might remove more useful data from the buffer cache. Starting with Oracle Database 12 c Release 1 (12.1.0.2), if the Oracle Database instance determines that there is enough space to cache the full database in the buffer cache and that it would be beneficial to do so, then the instance automatically caches the full database in the buffer cache.
When an instance is put in force full database caching mode, what happens?
When an instance is put in force full database caching mode, database objects are not loaded into the buffer cache immediately. Instead, they are cached in the buffer cache when they are accessed.
What is the easiest way to manage memory?
The easiest way to manage memory is to use the graphical user interface of Oracle Enterprise Manager Database Express (EM Express) or Oracle Enterprise Manager Cloud Control (Cloud Control).
What is memory management in Oracle?
Memory management involves maintaining optimal sizes for the Oracle Database instance memory structures as demands on the database change . The memory structures that must be managed are the system global area (SGA) and the instance program global area (instance PGA).
How to manage Oracle instance memory?
To do so (on most platforms), you set only a target memory size initialization parameter ( MEMORY_TARGET) and optionally a maximum memory size initialization parameter ( MEMORY_MAX_TARGET ). The total memory that the instance uses remains relatively constant, based on the value of MEMORY_TARGET, and the instance automatically distributes memory between the system global area (SGA) and the instance program global area (instance PGA). As memory requirements change, the instance dynamically redistributes memory between the SGA and instance PGA.
What is automatic shared memory management?
Automatic Shared Memory Management simplifies SGA memory management. You specify the total amount of SGA memory available to an instance using the SGA_TARGET initialization parameter and Oracle Database automatically distributes this memory among the various SGA components to ensure the most effective memory utilization.
What is SGA in Oracle?
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 SGA is shared by all server and background processes. Examples of data stored in the SGA include cached data blocks and shared SQL areas.
What is flash cache?
The flash cache is an extension of the SGA-resident buffer cache, providing a level 2 cache for database blocks. It can improve response time and overall throughput, especially for read-intensive online transaction processing (OLTP) workloads. The flash cache resides on one or more flash disk devices, which are solid state storage devices that use flash memory.
How does SGA memory management work?
With automatic shared memory management, you set target and maximum sizes for the SGA. The database then sets the total size of the SGA to your designated target, and dynamically tunes the sizes of many SGA components. With manual shared memory management, you set the sizes of several individual SGA components, thereby determining the overall SGA size. You then manually tune these individual SGA components on an ongoing basis.
Does SGA need real memory?
For optimal performance in most systems, the entire SGA should fit in real memory. If it does not, and if virtual memory is used to store parts of it, then overall database system performance can decrease dramatically. The reason for this is that portions of the SGA are paged (written to and read from disk) by the operating system.
What is memory management in Oracle?
Memory management is the process of allocating new objects and removing unused objects to make space for those new object allocations. This section presents some basic memory management concepts and explains the basics about object allocation and garbage collection in the Oracle JRockit JVM. The following topics are covered:
What is the allocation of large objects in Java?
Large objects that don’t fit inside a TLA are allocated directly on the heap. When a nursery is used, the large objects are allocated directly in old space. Allocation of large objects requires more synchronization between the Java threads, although the JRockit JVM uses a system of caches of free chunks of different sizes to reduce the need for synchronization and improve the allocation speed.
Does the JVM use more memory than the heap?
During the garbage collection objects that are no longer used are cleared, thus making space for new objects. Note that the JVM uses more memory than just the heap. For example Java methods, thread stacks and native handles are allocated in memory separate from the heap, as well as JVM internal data structures.
What is memory management in Oracle?
Memory management involves maintaining optimal sizes for the Oracle Database instance memory structures as demands on the database change.
How to manage Oracle instance memory?
To do so (on most platforms), you set only a target memory size initialization parameter ( MEMORY_TARGET) and optionally a maximum memory size initialization parameter ( MEMORY_MAX_TARGET ).
How to control PGA memory?
You can control this amount by setting the initialization parameter PGA_AGGREGATE_TARGET.
What is SGA_TARGET in Oracle?
With automatic shared memory management, you specify the total amount of SGA memory available to an instance using the SGA_TARGET initialization parameter and Oracle Database automatically distributes this memory among the various SGA components to ensure the most effective memory utilization.
What is database smart flash cache?
Database Smart Flash Cache is an extension of the SGA-resident buffer cache, providing a level 2 cache for database blocks. It can improve response time and overall throughput for both read-intensive online transaction processing (OLTP) workloads and ad hoc queries and bulk data modifications in a data warehouse environment. Database Smart Flash Cache resides on one or more flash disk devices, which are solid state storage devices that use flash memory. Database Smart Flash Cache is typically more economical than additional main memory, and is an order of magnitude faster than disk drives.
Why does Oracle not cache?
In default caching mode, Oracle Database does not always cache the underlying data when a user queries a large table because doing so might remove more useful data from the buffer cache. Starting with Oracle Database 12 c Release 1 (12.1.0.2), if the Oracle Database instance determines that there is enough space to cache the full database in the buffer cache and that it would be beneficial to do so, then the instance automatically caches the full database in the buffer cache.
When an instance is put in force full database caching mode, what happens?
When an instance is put in force full database caching mode, database objects are not loaded into the buffer cache immediately. Instead, they are cached in the buffer cache when they are accessed.
What is executable memory?
Executable memory means the memory pages that are used for program and library text. Anonymous memory means the memory pages that are not associated with files. For example, anonymous memory is used for process heaps and stacks. Filesystem memory means the memory pages that are used for file I/O.
What does low memory mean in Solaris?
Under low memory, Solaris begins to scan for memory pages that have not been accessed recently and moves them to the free list. On Solaris 8 or later, a non-zero value of sr means the system is running low on physical memory. You can also use vmstat -p to observe page in, page out, and page free activities. For example:
How to find how much memory is available?
To find how much free memory is currently available in the system, use the vmstat command. Look at the free column (the unit is KB). For example:
How to use pmap?
pmap can help answer many questions about application memory usage. For example: 1 If the application core-dumps because of a wrong pointer reference, you can use pmap <corefile> and address space information to see which memory area the wrong pointer pointed to. 2 For a 32-bit application, how much heap size the application could use depends on other items: stack size, the number of threads, library, the executable, and so forth. 3 If you need to specify a shared-memory base address, you must be familiar with address spaces. The shared-memory base address should be lower than the addresses of loaded libraries and thread stacks already created, but higher than heap addresses. However, manually specifying a shared-memory base address is not encouraged in Solaris; see the man page for shmat (2). Using a fixed value for the shmaddr argument can adversely affect performance on certain platforms because of D-cache aliasing.
What is free memory in Solaris?
The free list is the amount of memory that is actually free. This is memory that has no association with any file or process. The cache list is also the free memory; it is the majority of the file system cache.
Can you create a ramdisk with ramdiskadm?
You can create a ramdisk with ramdiskadm (1M) as a block device. The ramdisk uses physical memory only. By default, at most 25 percent of available physical memory can be allocated to ramdisks. The tmpfs file system uses virtual memory resources that include physical memory and swap space.
How to allow Oracle to take full control of memory management?
To allow Oracle to take full control of the memory management, these parameters should be set to zero. If you are using UNIX/Linux, before you consider using AMM you should check the current size of your shared memory file system. On Linux you do this by issuing the following command.
What is memory_target in Oracle?
MEMORY_TARGET: The amount of shared memory available for Oracle to use when dynamically controlling the SGA and PGA. This parameter is dynamic, so the total amount of memory available to Oracle can be increased or decreased, provided it does not exceed the MEMORY_MAX_TARGET limit. The default value is "0".
What is memory_max_target?
MEMORY_MAX_TARGET: This defines the maximum size the MEMORY_TARGET can be increased to without an instance restart. If the MEMORY_MAX_TARGET is not specified, it defaults to MEMORY_TARGET setting.
How many V$ views are there in Oracle 11g?
In addition to the existing memory management V$ views, Oracle 11g includes four new V$ views to support automatic memory management:
