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Closed 11 years ago.
What is SGA? Can you explain me in a simple manner?
The Oracle documentation does a pretty good job. An excerpt follows:
The SGA comprises a number of memory components, which are pools of
memory used to satisfy a particular class of memory allocation
requests. Examples of memory components include the shared pool (used
to allocate memory for SQL and PL/SQL execution), the java pool (used
for java objects and other java execution memory), and the buffer
cache (used for caching disk blocks).
Related
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Closed 9 years ago.
While preparing for an exam, I came across this doubt. Does a CPU process instructions as data?
The short answer is yes. There's a Wikipedia entry on it. The gist of it is, if you have the address of the instructions you would like to read, then you can load those into data registers, test the instructions, and even write back new instructions. Many modern operating systems will probably not allow you write the instructions back however. It is a safety precaution to prevent malicious code from modifying your system, or trust applications.
Depends on the computer:
In von Neumann architecture, yes.
In Harvard architecture, no.
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Closed 10 years ago.
Do we really need a caching layer when using a nosql datastore? I understand the use case when using a traditional sql db, the overhead of query processing can be avoided by a simple key/value lookup. But in the case of nosql, that's not the case anymore. Also, the cache instances are almost always running in separate instances, which means they still have the same network delay associated with accessing a nosql datastore.
Thanks!
Caching is simply a tool for performance optimization and should be treated as such. This means doing some load testing to see what gains (if any) your performance enhancements give.
Most NoSQL servers do make claims to be much faster than traditional RDBMS but only testing it out will tell you if they're faster for your applications and infrastructure.
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Closed 10 years ago.
What is the difference between storing sessions in file and in database?
The primary difference is that fetching the session info from a database can be quite a bit faster than from a file system. This is partly because of DB caching, but also because if there are large numbers of sessions files the file system may not cope well with it. Most file systems start to degrade when there are a few thousand files in a single directory, whereas DBs don't run into this problem.
Other reasons include fine-grained security, replication, and/or sharding, all of which are meat and potatoes to DBMSes, but not to filesystems.
If you only have a few sessions it doesn't matter, but when there 10,000 or 10,000,000 sessions it definitely does.
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Closed 11 years ago.
My multicore machine is receiving packets and distributes them evenly (sort-of round robin) among its cores. Each core should decide whether to let the packet pass or drop it, depending solely on its origin address.
I need to find lock-less algorithm and data structure to allow this. Can you help?
If you are happy to use Java, or look at the design of Java source, you could chose a random key and then retrieve a queue from http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/ConcurrentHashMap.html. Given the queue, you could add the packet to it without blocking if it was a http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/ConcurrentLinkedQueue.html
Much of java.util.concurrent is due to Doug Lea, who has information on it at http://gee.cs.oswego.edu/dl/concurrency-interest/index.html.
Possibly overkill for your particular problem, but might satisfy a general request for info on data structures in this area.
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Closed 11 years ago.
I came across NUMA-aware allocation in relation to improving the performance of the application. It is something related to Multicore programming. I know NUMA means non-uniform memory access but I am not aware of NUMA-aware allocation.
Do anyone know about this?
NUMA aware allocation is basically the ability to allocate resources in a way such that the NUMA-properties of the system does not result in unnecessarily long commnication paths. I.e memory should be allocated in the RAM connected directly to the CPU where the process needing it runs, etc