Oracle Database Discussions

hi guys,

http://docs.oracle.com/cd/E11882_01/server.112/e25494/onlineredo002.htm#i1306224

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Datafiles should also be placed on different disks from redo log files to reduce contention in writing data blocks and redo records.
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I am really thinking whether is there actually any contention when first of all oracle can only writes to 1 redo log files at a time.
http://docs.oracle.com/cd/E11882_01/server.112/e25494/onlineredo001.htm
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Oracle Database uses only one redo log files at a time to store redo records written from the redo log buffer. The redo log file that LGWR is actively writing to is called the current redo log file.
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so the process flow i got after reading this chapters is that

when LGWR fills up a redo log file ( the redo records) then there will be a log switch + checkpoints where the writing to the data blocks occur. There seem to be a serial flow rather then a concurrent kind of flow. So i don't really get it when it mention there will be contention when both datafiles and redo records writing which is the redo log file are on the same disks.

Just to confirm with you guys whenever there is a log switch a checkpoint will occur too right.
http://docs.oracle.com/cd/E11882_01/server.112/e25494/onlineredo002.htm? U can seach checkpoint to jump to the section it mention from this documentation.