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February 2008

3-2-1 Initialize

A while ago I went on a crusade within my organization to review and clean up our init.ora files.  Many of them had been around since versions 7.3 and 8.1 of Oracle and were simply added to over time.  I still like the text-based init.ora files that I can check into source code control and liberally comment.  I’m liking the fact that you can comment on parameters in spfiles too — they even have the comment fields displayable in DB Console and Grid Control.

I’m constantly amazed at the places I go where I still see the following text in their init.ora files:

# Use the following table to approximate the SGA size needed for the
# three scenarios provided in this file:
#                     ——-Installation/Database Size——
#                      SMALL           MEDIUM           LARGE
#  Block         2K    4500K            6800K           17000K
#  Size          4K    5500K            8800K           21000K

I’m guessing the init.ora file isn’t being reviewed at those places. :-)

Anyway, I started doing this when I realized that many of the default values for particular parameters were higher / better than the ones we had “set”.  And we didn’t have any documented reasons for setting them.  I ended up with 2 goals:

  1. When the default values provided by Oracle are greater than or “better than” the values we had “set”, remove the parameter from the file
  2. When we need to set a parameter, we need to include a comment as to why for each and every parameter

End result was a lot more clarity around our settings and why we needed them.  We also were able to basically make an init.ora template for ALL databases, since we made such heavy use of defaults.

Man is a stream whose source is hidden

I’d like to direct your attention to Chen Shapira’s latest blog entry, in which she talks about Oracle Streams.  Having been a replication aficionado for years, I’ve always been interested in Streams, but slightly awed by their complexity and flexibility.  I’m looking forward to the follow-up entries, as I’ve recently begun working with them myself.  Perhaps we can all add to the collective knowledge on them.  I can say this, you’ll be learning a lot about things you may not have played with before: Advanced Queuing (especially propagation), LogMiner, and (coolest of all, in my opinion) networked DataPump (in 10g and up).  Just try to keep focused on what you’re trying to do and break Streams down into Capture processing, Propagation processing and Apply processing.  Even though it’s about the older Advanced Replication, you may even want to read my old paper.

SQL*Net message to client vs SQL*Net more data to client

After my last post about SQL*Net message to client wait event I had a follow-up question about what’s the difference between SQL*Net message to client and SQL*Net more data to client wait events. I’ll post the answer here:

The first session data unit (SDU) bufferful of return data is written to TCP socket buffer under SQL*Net message to client wait event.

If Oracle needs to return more result data for a call than fits into the first SDU buffer, then further writes for that call are done under SQL*Net more data to client event.

So, whether and how much of the SQL*Net more data to client vs. SQL*Net message to client waits you see depends on two things:

SQL*Net message to client wait isn’t really what it’s thought to be

In a recent Oracle Forum thread a question came up how to use SQL*Net message to client wait events for measuring network latency between server and client. The answer is that you can’t use it for network latency measurements at all, due to how TCP stack works and how Oracle uses it.
I’ll paste my answer here too, for people who don’t follow Oracle Forums:
As I wrote in that reply, “SQL*Net message to client” does NOT measure network latency!

Oracle hidden costs revealed, part 1 – Does a batch job run faster when executed locally?

This series is about revealing some Oracle’s internal execution costs and inefficiencies. I will analyze few situations and special cases where you can experience a performance hit where you normally wouldn’t expect to.

The first topic is about a question I saw in a recent Oracle Forum thread.

The question goes like this: “Is there any benefit if I run long sql queries from the server (by using telnet,etc) or from the remote by sql client.”

In order to leave out the network transfer cost of resultset for simplicity, I will rephrase the question like that: “Do I get better performance when I execute my server-side batch jobs (which don’t return any data to client) locally from the database server versus a remote application server or workstation?”

Excellent article on Oracle 11g PL/SQL function result cache

I have so far avoided writing such pointer blog posts which only refer you to another article, but I have to do it with this one. Adrian Billington has written an excellent article on performance of Oracle 11g PL/SQL function result cache. His article is a good example of a thorough, well organized and well written technical content. I really enjoyed reading it and thanks to his thoroughness, he has just saved me some precious time doing that research on my own.