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Don Burleson Blog 








Important suboptimal blocksize alert

4 August 2008

Oracle wunderkind Steve Karam recently published a note about getting a 270x performance improvement after changing blocksize.

"When the update was run against the 16k blocksize DB, it took 45 minutes.

Against the 4k blocksize DB on the same box with the same parameters and the same FS mounts, it took 2 minutes 20 seconds."

After investigation, it was noted that this issue may have been precipitated by a long-term bug (present in Oracle 19, 10g and 11g).  It is recommended that you avoid the a 16k blocksize configuration with ASSM (a.k.a. bitmap freelists, Automatic Segment Space Management).

Bitmap freelists are great for relieving buffer busy waits, but they appear somewhat buggy, and there are also performance issues when using ASSM under high DML loads.

Also see these notes on suboptimal performance related to blocksize.

For more details on the important impact of blocksize in Oracle, see my notes here.


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