Question

在Oracle中,当用户要执行SELECT语句时,哪个进程从磁盘获得用户需要的数据

Answer 1

各位不要误人子弟呀。应该是服务进程(server process)
ORACLE进程分后台进程跟服务进程，DBWR是后台进程，它只负责将DBBUFFER脏数据写到数据文件，是单向的。而与用户进程对应的服务进程则将数据块读到SGA。
concepts上写的很清楚：
Oracle processes run the Oracle server code. They include server processes and background processes.

Server processes (or the server portion of combined user/server processes) created on behalf of each user's application can perform one or more of the following:

1.Parse and run SQL statements issued through the application
2.Read necessary data blocks from datafiles on disk into the shared database buffers of the SGA, if the blocks are not already present in the SGA
3.Return results in such a way that the application can process the information

Answer 2

DBWn将相关磁盘数据读到data buffer cache中去。
并负责将data buffer cache中的脏数据块写入磁盘。

查过concepts了果然是我错了。
受教了。多谢

When a client process requests a buffer, the server process searches the buffer cache for
the buffer. A cache hit occurs if the database finds the buffer in memory. The search
order is as follows:
1. The server process searches for the whole buffer in the buffer cache.
If the process finds the whole buffer, then the database performs a logical read of
this buffer.
2. The server process searches for the buffer header in the flash cache LRU list.
If the process finds the buffer header, then the database performs an optimized
physical read of the buffer body from the flash cache into the in-memory cache.
3. If the process does not find the buffer in memory (a cache miss), then the server
process performs the following steps:
a. Copies the block from a data file into memory (a physical read)
b. Performs a logical read of the buffer that was read into memory.

Answer 3

应该是DBWR

Answer 4

服务器进程