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Oracle db_block_size and row load rate

Oracle Tips by Burleson Consulting
March 23, 2004
Don Burleson

Sometimes I get comments from other Oracle experts who challenge even the most obvious assertions about Oracle behavior.  Recently I received a comment from an Oracle employee who challenged the widely-held belief using a large db_block_size will speed-up data loads.  Here was my original statement, based on my clients experiential evidence:

    Use a large blocksize - Data loads onto 32k blocksizes will run far faster because Oracle will be able to insert more rows into an empty block before a write.

Well, whenever I say something obvious, my teenage daughter says it best, replying "Well Duh".  Mind you, I've never been in the habit to having to "prove" the obvious, but I thought it might be fun to run a small experiment. 

Of course, these tiny experiments on single CPU server with a single user are rarely valid for large-scale production systems, but hey, it worked.  Here is my small single-CPU, single-user benchmark showing the performance of loads into a larger blocksize:

alter system set db_2k_cache_size=64m scope=spfile;
alter system set db_16k_cache_size=64m scope=spfile;
startup force
create tablespace twok blocksize 2k; <-- using ASM defaults to 100m
create tablespace sixteenk blocksize 16k;
create table load2k tablespace twok as select * from dba_objects; < creates 8k rows
drop table load2k; <- first create was to preload buffers

 
set timing on;
create table load2k tablespace twok as select * from dba_objects;
create table load16k tablespace sixteenk as select * from dba_objects;
 
For a larger sample, I re-issued the create processes with:
select * from dba_source; -- (80k rows)

Even with this super-tiny sample on Linux using Oracle10g (with ASM) the results where impressive:

       				  2k     	  16k
				  blksze         blksze
8k table size			4.33 secs    	4.16 secs  
80k table size			8.74 secs    	8.31 secs 
 
So, does this "prove" that my assertion is correct?  Not really.
 
In real-world databases with thousands of concurrent users and hundreds of transactions per second, small experimental "proofs" are largely meaningless.  In sum, I am always wary of anyone who claims that they can prove the way that Oracle behaves with a code snippet.
 
In the real-world, the universal answer to any Oracle-related assertion is "it depends".  I have no doubt that some clients might experience faster load speeds with smaller blocksizes, depending on their unique configuration.  Such is the nature of Oracle tuning!


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Mike Ault, one of the world's most widely-read Oracle experts, has finally consented to release his complete collection of more than 450 Oracle scripts, covering every possible area of Oracle administration and management.

This is the definitive collection of Oracle monitoring and tuning scripts, and it would take thousands of hours to re-create this vast arsenal of scripts from scratch.

Mike has priced his complete collection at only $39.95, less than a seven cents per script.  You can download them immediately at this link:

http://www.rampant-books.com/download_adv_mon_tuning.htm



 

 

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