Use Write Caching to Optimize High Volume Data Driven Applications
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by Steven Smith
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Test – Cache Reads and Writes

For the final test, both reads and writes will be cached to optimize performance.  Naturally, this will have the best performance of the three scenarios we’ve examined (no caching, read caching, read-write caching).  For this test, I enabled batch updates (write caching) in addition to the read caching enabled in the previous test scenario.  I set both caching periods to 10 seconds and ran the test on two system configurations just as before (remote database, local database).  Figure 11 shows a graph of the results.  The blue line (1) indicates the setup with the remote database.

Figure 11 – Test Results With Read and Write Caching Enabled


As you can see, the difference between the two configurations is almost zero, and the total requests per second is significantly higher for both configurations (though obviously much more so for the remote database option).

Note: The remote configuration option tended to have regular drops in requests per second in every scenario tested (but most noticeable in this last graph).  I’m not sure what the cause of this is, but since the behavior was consistent across all of my tests and only lasted a few seconds, I concluded that whatever was causing it was not related to my caching, nor would it have a significant effect on my statistics.  I couldn’t tie it to garbage collection or the connection pool running low, based on the performance counters I collected.

More Details

Test 1 (Blue) averaged 113.1 ASP.NET requests/second.  Test 2 averaged 118.52 ASP.NET requests/second.  For Test 1, the web server’s CPU averaged 69.62%.  For test 2, the web server CPU (and also the db server) averaged 72.9%.  Average Time to Last Byte (TTLB) in Test 1 for each whole page was 3.95ms.  For Test 2, it was just 3.52ms.

Looking at the database, in Test 1, the remote database averaged 1.24 Batch Requests/sec.  In Test 2, the local database averaged 0.6 Batch Requests/sec.  I’m not sure why there is such a discrepancy here, but they’re both much lower than in the previous tests.

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User Comments

Title: Modern SQL XML Support   
Name: Steve Smith
Date: 2008-08-08 2:33:41 PM
Jason Follas posted recently on how to do the SQL XML work more efficiently in SQL 2005+:
Title: MSMQ   
Name: Derek
Date: 2008-01-14 9:37:07 AM
Thanks for the article. Having some experience with MSMQ I can tell you it will probably perform well, but we've had a lot of issues with using it in a clustered environment. This is a well-known shortcoming of MSMQ.

We've gone to some 3rd party pub-sub solutions that work much more efficiently and work well in a clustered environment.
Title: Using a synchronized HashTable   
Name: Tim
Date: 2005-08-22 1:41:25 PM
Also, how would this be affected by using Hashtable.Synchronized(...) to create the hashtable. It appears that automatically protects the hashtable's Add method and the indexing property Set accessor with a lock, which would protect you during writes.
Title: What about the code for updating the item in Cache?   
Name: Tim
Date: 2005-08-22 12:08:14 PM
Can you show sample code for updating the item in Cache? For example, if item is added to cache with certain expiration, etc., when you update it, do you have to add it back with the same parameters, or do you just reference it like Cache[myitem] = updatedValue, and it will retain all previously set values...

Title: Programmer   
Name: Microfolx
Date: 2005-05-21 10:33:19 AM
This is a very nice site. Keep it up.
Title: Re: Consistency   
Name: Brett
Date: 2005-05-20 5:15:54 PM
Nice article... I might consider trying normal XML writers rather than StringBuilder. Or even XML serialization. Probably slightly slower, but reduces errors.

On the point regarding charging for page views. I have two suggestions. One is to periodically reload the current click count from the database and not worry about being exact. Hey if they get 1 million or 1,005,000, does it really matter? This isn't the space shuttle. The second would be to switch to a non-caching code path when you get close to whatever your maximum value is. So when you hit, say 990,000 views (based on your hit rate, etc.) then switch to the non-caching version for that customer.
Title: Consistency   
Name: Brian
Date: 2005-05-20 2:03:29 PM
I had to accomplish this exact same scenario. The problem I ran into was the caching. Lets say that one of your advertisers pays you to show their ad 1 million times. How can you insure that it doesn’t go over? If you are holding the most current counters in cache, won’t each process be looking at their own cache, not to mention each server in the web farm and all it’s processes be looking at their own cache.

Another general Cache question. When I write something to cache, isn’t it only available for that particular process? So if you setup your application to have 5 worker processes, won’t that have 5 separate cache entries?
Title: web farm   
Name: parker
Date: 2005-04-24 3:19:08 AM
How do you account for disperate sessions in a web farm scenario? Is the cache shared amoung the servers?
Title: Too Good   
Name: Zulfiqar Damani
Date: 2005-04-18 12:46:36 AM
It presented very well, also it was interesting too.
Title: Thanks   
Name: Happel
Date: 2005-04-14 8:23:23 AM
Thanks for sharing this article, very interesting.

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