Two days until I leave for Asia. (You have no idea how busy I’ve been for the past month!) If anyone’s curious about trip details I’ve posted about it over on the non-technical side of my blog.

http://www.ardentperf.com/2007/09/27/two-days-until-asia-trip-update/

In two days I will be en route to Asia! For the next two weeks we will be visiting several families working in China, Cambodia and Thailand to learn about what they do and offer support. I’m so excited - but I can’t even begin to tell you just how busy I’ve been over the past month! My sincere apologies for not sharing much about this trip sooner; I’ve really just been that busy. In the month prior to this week I only slept in my own bed six or eight times.

So anyway, Erin (who’s also going on the trip) wrote this great summary of what we’ll be doing and so I’m just going to post her letter.

From: Erin C
Date: Sep 26, 2007 10:16 AM
Subject: 3 days til ASIA! Trip Update.

In THREE days I will be flying over the top of the world to Asia! Three days. Three. Days. Wow.

What an experience it has already been — I’ve been reading about Theravada Buddhism, the predominant religion claimed by people in Thailand and Cambodia; I’ve visited the newly opened Cambodian museum in Chicago and learned about the deep-rooted hope that persists in a people whose country is still torn apart from Pol Pot and the Kmer Rouge regime; I’ve gone shopping at a Vietnamese/Thai grocery store so I could prepare a delicious Thai dessert (mango sweet rice– yum!); and, yes, I’ve even learned how to say “vegetarian,” as well as other key phrases, in Thai, Kmer (Cambodian) and Mandarin.

Throughout it all I have been praying with focus and determination that’s unique even for a stubborn girl like me. And I know my prayers have been joined with prayers from so many different people. I cannot express to you how necessary that has been, and how much that means to me.

I am so humbled at how God takes care of the smallest details in preparation for this trip. As a case in point, I came home yesterday rather late in the evening and there was a fed ex envelope on the coffee table with my name on it. Opening it up, I found that it was a check written out to me from a dear, dear friend for $100, the exact amount that I need to bring over with me to cover food expenses for the trip. I literally cried. What an amazing God: he loves us and knows exactly what we need. I am so humbled.

I’ve been promising a trip update for awhile now, so I will give you a brief overview of the places that we are going to be going and what we are going to be doing while in Asia. It is going to be a whilrwind trip, with the longest stay in any one place being 3 days.

China: We will stay in the Yunnan province, somewhat near the city of Kunming. The organization that the family from church began is doing cutting edge social service work in the area involving everything from medical care to education. The thing that I like best about this organization is that they select and train indigenous men and women to be leaders and trainers themselves. I love that! What a way to help a community build itself up and take care of each other in a sustainable way!

Thailand: In complete contrast to China, in Thailand we will stay in Bangkok — the capital and largest city. The family from the church in Thailand runs a ministry that is an outreach to women and children involved in prostitution. Thailand is immensely involved in sex trafficking; many women and children are forced into it, others are lured by the promise of money, and others enter out of sheer desperation. The ministry helps equip women and children with job and technical skills to make money outside of prostitution. They also provide the emotional and spiritual support so crucial for escaping from this trap. While in Bangkok, we will spend two nights doing bar outreach and days working with the women and children in their classes.

Cambodia: In Cambodia we will visit the large city of Pnom Penh and then will stay with the missionary family in a small village. Cambodia is still reeling after the 4 years under Pol Pot and the Kmer Rouge. For those a little shakey in Cambodian history (I was, before I began researching), Pol Pot was in power for only 4 years, but over a million Cambodians were killed during that time, some starved or died from overwork in the “killing fields” where they were to be “re-educated” and some were outright assasinated by the new regime. The United States also systematically bombed the country (part of a “strategy” during the Vietnam war) and a million more Cambodians are estimated dead from that. During these years, all currency was abolished and school systems (elementary to university) shut down. Temples, art, and music were destroyed. This was part of the plan to create an agrarian system in which all were equals. What this means for the country now is that most Cambodians are extremely poor, in a way that the poorest in the United States cannot fathom. Literacy is almost nonexistant in some parts of the country, and schools are still rare. One fact that stood out for me from my experience at the Cambodian museum was the story that most teachers can only work one day a week because they simply cannot sustain their families on the tiny income that teaching provides. And I thought teachers here were poorly paid! The family we’re working with in the village is focused on teaching and medical/dental care for the villagers.

Prayers:

• spiritual protection
• friendship that crosses cultural and language boundaries
• health and travel safety
• most of all, that the glory of God shines through all and in all

Thank you so much for your faithful prayers and support. I truly have no words to express the depth of my appreciation and my joy that you have joined me in this call. May God’s love delight you more and more each day!

Peace,
Erin

–
“I love the recklessness of faith– first you jump, then you grow wings.” ~William Sloane Coffin

Last night I posted a case study where I used the AWR (a blessed new feature) to investigate “gc buffer busy” wait events in a RAC environment. I concluded the write-up by theorizing that the single freelist was pointing all nodes of the cluster to the same small group of blocks for inserts and thereby causing the blocks on the freelist to always be subject to unearthly contention across the cluster.

One common piece of advice for gc buffer busy waits is to treat them like regular buffer busy waits. Because essentially that’s what they are - a buffer busy wait on a remote instance. So another avenue of investigation is to look at what might be causing buffer busy waits across the cluster.

Some people may remember that back in the days before YAPP and the wait interface, latches were usually where the purported “experts” looked when you had performance problems. Particularly those two infamous latches cache buffers chains and library cache. And of course today these are still an important part of any in-depth investigation and V$LATCH even includes wait time so you can take a time-based approach to analysis. I spent some time yesterday having a look at the latching in this RAC system and it yielded some results that I thought might be interesting to post. So here goes…
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Well I don’t have a lot of time to write anything up… sheesh - it’s like 10pm and I’m still messing with this. I should be in bed. But before I quit for the night I thought I’d just do a quick post with some queries that might be useful for anyone working on a RAC system who sees a lot of the event “gc buffer busy”.

Now you’ll recall that this event simply means that we’re waiting for another instance who has the block. But generally if you see lots of these then it’s an indication of contention across the cluster. So here’s how I got to the bottom of a problem on a pretty active 6-node cluster here in NYC.

Using the ASH

I’ll show two different ways here to arrive at the same conclusion. First, we’ll look a the ASH to see what the sampled sessions today were waiting on. Second, we’ll look at the segment statistics captured by the AWR.

First of all some setup. I already knew what the wait events looked like from looking at dbconsole but here’s a quick snapshot using the ASH data from today:
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So this is the view from the 12th floor of the hotel I’m staying at in NYC this week. I didn’t realize this when I booked my room… but it turns out that this is the same hotel where the song “Pennsylvania 6-5000″ was written! And this is the hotel it was written about!

Not only that, but when I asked how I should get to work I was promptly told to “Take The A Train”. So I did.

Just sent this to someone in an email and it seems like something that could be useful for everyone. They were asking how to determine the best setting for db_file_multiblock_read_count. First off, you probably will need assistance from a system admin or SAN admin if you’re running on a SAN. And contrary to one popular belief, it is very possible that setting this parameter too high can cause performance degradation. [Max I/O chunk size] / [db_block_size] is not necessarily the best value for the MBRC. Yes Steve Adams has a script to determine the max possible size for your system - but that doesn’t necessarily mean that this is the best value.

Also, note that getting system statistics is far more important than the MBRC value. It’s really critical that you get good system stats in place so that Oracle costs the read operations far more accurately. For more a good overview of system statistics check out Jonathan Lewis’ article on OTN, Understanding System Statistics.
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