Oracle log file parallel write

log file parallel write

Writing redo records to the redo log files from the log buffer.

Wait time

Time it takes for the I/Os to complete. Even though they are written in parallel, one needs to wait for the last I/O to be on disk before the parallel write is complete.

Parameters

files

Number of files written to.

blocks

Number of blocks to be written.

requests

Number of I/O requests.

Advise

Especially during insert operations a lot of redo will be generated. The log I/O size could be come very large (over 200K). Writing a chunk of  256K can take up to 429 msec (for Filesystem) and 115.6 msec (for Raw Device). So moving the redo log files to a Raw Device will reduce the wait almost by a factor of 4 (429 msec versus 115.6 msec). The next thing to do here is to stripe the logfile over for example 8 disks with a strip size of 32K. The write of 32K takes 19.3 msec versus 115.6 msec.  The writes to the 8 stripes will happen in parallel, so with some setup time for these I/O’s the time may be 24 msec for each I/O (which happen in parallel).

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