Re: buffer cache structure in SGA

From: Mladen Gogala <>
Date: Mon, 2 Apr 2018 16:02:24 -0400
Message-ID: <>

That is a classic and brilliant paper. It is interesting to see how the numbers went down for an order of magnitude. With the flash drives, IO latency is no longer 10 millisecond, it is now < 1 millisecond.  Similarly, for memory access with the latest DRAM4 sets, the latency is smaller than 1 microsecond, it's about 100 nanoseconds. Also, in Oracle 12c, it is possible to use threaded implementation, with pthread mutexes instead of latches. Since pthread mutexes do not execute system service, no raising of IPL is needed and the whole thing will be less CPU intense. However, the basic premises of your article still hold true:

  1. LIO is not free.
  2. Latches needed for block hash manipulation are still expensive in terms of CPU
  3. Read in a consistent mode can come at a significant cost, because of the undo operations.

The numbers are from the time of Oracle 8i. The numbers are no longer true for the modern systems. However, the basic principles covered in the article and the whole article itself are still relevant. It's very interesting to re-read the same article after all these years. Thanks for the opportunity.


However, the paper is still very relevant, because it points out the internal

On 04/02/2018 11:14 AM, Cary Millsap wrote:
> Cary Millsap
> Method R Corporation
> * Author of /Optimizing Oracle Performance
> <>/ and /The Method R Guide to Mastering
> Oracle Trace Data, 2nd edition <>/
> On Sat, Mar 31, 2018 at 12:57 PM, Orlando L <
> <>> wrote:
> HI
> I am reading a book on internals. It talks about Hash latch, hash
> bucket, hash chain, buffer header etc and contention for those
> things. I somewhat understand what a latch is, but do not know
> what a 'bucket', 'chain', are.  Is there a paper that explains
> them in detail at a basic level. thanks.
> Orlando.

Mladen Gogala
Database Consultant
Tel: (347) 321-1217

Received on Mon Apr 02 2018 - 22:02:24 CEST

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