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Don Burleson Blog 







Getting around the high costs of Oracle logical I/O

Oracle Tips by Burleson Consulting
March 30, 2004
Don Burleson

As RAM storage becomes cheaper than ever, many companies are exploring the issue of fully-cached Oracle databases.  As I noted in an earlier Oracle tip, solid-state disk is changing the way that Oracle professionals and manage and tune their databases.

One of the issues is the relatively high-cost of fetching an Oracle data block from disk.  In theory RAM is 10,000 times faster than disk milliseconds vs. nanoseconds), but when you add-in the overhead of lock serialization and latches, a logical I/O might be less than a thousand times faster than a "physical" disk I/O.

In an article in they note a new company called InfoCyclone that recognizes the kludgy block-based approach to Oracle RAM I/O.

This tool detects frequently-referenced data and caches it is it's high-speed version of the Oracle data buffer.  According to the article:

"You might ask why you shouldn't use Oracle's caching. Well, you could. But Oracle effectively treats a cache as a sort of memory-oriented disk: it still uses a block-based approach, you have to check whether the data you want is on disk or in cache, you have to check with the cache is clean or dirty, and so on. All of which incurs an overhead that InfoCyclone avoids."

We also see companies such as Texas Memory Systems offering solid-state disk replacement for the Oracle data buffer cache to speed-up I/O at the physical level:

Still, we see some companies such as UNISYS getting blistering performance from Oracle (on Windows, no less) using 100 gigabyte db_cache_size and db_keep_cache_size:

Got scripts?

 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.

Mike has priced his collection of 465 scripts at $39.95, less than a dime per script.  You can download them immediately at this link: 



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