oracle中的共享内存和信号量的一个简单解释

转载于 2008-07-31 09:22:40 发布 · 178 阅读

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本文介绍了Oracle如何利用共享内存创建系统全局区(SGA)，并解释了信号量在此过程中的作用。当Oracle进程访问SGA时，会检查相应内存区域的信号量状态，以避免并发冲突。

Shared memory allows an application to allocate a chunk of memory which can be viewed by other processes. Oracle uses shared memory to create the System Global Area (SGA) which all Oracle processes must be able to access.

Semaphores act as flags for shared memory. Semaphores are either set on or off. When an Oracle process accesses the SGA (in shared memory) it will check for a semaphore for that portion of memory. If it finds a semaphore set on for that portion of memory that process will sleep and check again later. If there is no semaphore set on for that portion of memory it will set one on and proceed with its operation. When it is done it will switch that semaphore back to off.

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