Quote:
Originally posted by jmodic
If you've got Jonathan Lewis's book "Practical Oracle 8i" somewhere near by, open it on page 192-193 (Chapter 10: "Files, Raw and RAID"). You'll see there in Table 10-1 the performance impact of block size missmatch. In short, with 8K OS block size, the time required to do 1,000 random writes to a file with DB_BLOCK_SIZE=4K was 25.7 seconds, while with DB_BLOCK_SIZE=8K it only took 15.6 seconds for the same operation. I think the points made there by Jonathan are quite sufficient supporting evidence that choosing DB_BLOCK_SIZE smaller than OS block size certanly bears some performance degradation for writes.
For those of you that don't have that book available, let me just quote Jonathan explanation what happens when DBWR has to write a block (let's say 4K database block) to the file (that resides on a file system that has 8K OS block size):
P.S. It's not very clear from the original poster's question whether he uses "normal" block-based UFS, or maybe some newer extent-based Fast File System, like VxFS. I'm writing this with the assumption that he is talking about normal Unix File System,
That makes sense.