ColdFusion Performance

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When analyzing ColdFusion's performance, There are several things to keep in mind including JVM (memory) settings, slowness on the database tier, and memory leaks that can be easily avoided.

JVM Settings

Sizing the Heap

Memory Allocation

Trying to find the right size for your server's ColdFusion memory heap is an iterative process. However, the following memory allocation arguments will give you a good start: 
java.args=-server -XX:+UseCompressedOops -XX:+DisableExplicitGC -Xms1024m -Xmx2048m -XX:NewRatio=4 -XX:SurvivorRatio=8 -XX:PermSize=256m -XX:MaxPermSize=512m -Xss512k

Note: The above arguments only control memory allocation. You should still retain any garbage collector and class-related arguments.

The settings shown above specify a maximum ColdFusion heap of 2 GB (2048 MB), an Eden/New space (where Java creates new objects) that is 1/4 the size of the heap, and a non-heap Perm space with a maximum of 512 MB. If your application needs a bit more memory, you can adjust the "-Xmx" and "-Xms" values as needed. Setting the maximum heap argument (-Xmx) to a value higher than the minimum heap argument (-Xms) will allow ColdFusion to utilize more RAM during times of peak activity. This will increase startup time slightly, but it gives the server more stability when your sites are busy.

Choosing a Garbage Collector

After specifying good memory settings for your ColdFusion server, you'll want to ensure it uses an appropriate garbage collector for the work being done on your sites.

Mostly Concurrent Collector
If the sites on your server are primarily lightweight request/response applications where response times are critical, then the mostly concurrent garbage collector is a great choice for your server. This collector does its best to collect dead objects from memory while applications on the server are still processing data. This adds a small bit of overhead for transactional applications, but it helps such applications maintain their response-time SLAs. To enable this garbage collector, add the following JVM arguments after your memory allocation settings: 
-XX:+UseConcMarkSweepGC -XX:+UseCMSInitiatingOccupancyOnly -XX:+CMSClassUnloadingEnabled -XX:+CMSScavengeBeforeRemark -XX:CMSInitiatingOccupancyFraction=68 -XX:+UseParNewGC

Note: The main downside of this collector is that it can consume too much CPU when memory-intensive applications run on the server. Servers running such applications would want to use the throughput collector mentioned below.

Throughput/Parallel Collector
If the applications on your server are memory intensive and allocate a lot of objects, then the throughput/parallel garbage collector would be a great choice for your server. Any application performing image manipulation or creating a lot of objects would be a great candidate for the throughput collector. To enable this garbage collector, add the following JVM arguments after your memory allocation settings: 
-XX:+UseParallelOldGC -XX:YoungGenerationSizeIncrement=50 -XX:TenuredGenerationSizeIncrement=25 -XX:AdaptiveSizeDecrementScaleFactor=10 -XX:MaxGCPauseMillis=10000 -XX:GCTimeRatio=19

The first thing to note about this collector is the -XX:+UseParallelOldGC name. This doesn't mean you're using old garbage collection techniques; rather it mean that both the old (or tenured) and the new (or eden) sections of memory are collected in parallel. This allows Java to perform collections much faster than normal. One thing to keep in mind is that with this collector when the heap fills up Java will pause all application processing for a short period of time to clean up memory. The above settings act to minimize the time of such pauses so your end users typically won't notice any slowness.

References

Garbage Collection Performance Logging

Because a lot of the JVM's processing time can be spent in garbage collection of memory, it can be helpful to enable Garbage Collection Logging to your server. In order to do so, just add the following arguments to your ColdFusion server's jvm.config file: 
-Xloggc:gc-1.log -XX:+PrintGCDetails -XX:+PrintTenuringDistribution -XX:+PrintGCTimeStamps

If you wish to change the name of the log file, just change 'gc-1.log' to the filename you wish. By default, this file will be created in the same folder as your jvm.config file.

NOTE: This section primarily applies to VPS/Dedicated customers only. Our administrators make sure the Heap is properly sized on our shared ColdFusion servers.

Tuning the Database Tier

Add Indexes

Make sure all database fields are indexed properly, adding indexes for any columns used in a WHERE clause.

Tune Your Queries

Be sure to remove any 'SELECT *' statements in the code. Instead, explicitly name each column used in a query. Also, make use of query advisors such as the following:

Cache Queries (cfquery / cfstoredproc) Where Possible

Does your application have queries that could be cached? If so, enable caching on those queries as shown here: Good Developers Practice Safe Query Caching

The main takeaway is that your application should use the cachedwithin attribute on as many cfquery and cfstoredproc tags as possible. Query caching helps reduce the load on the database server and improves page response time noticeably.

To enable this attribute on your queries, just add the cachedwithin attribute to your cfquery or cfstoredproc tags. This example will cache a query for 1 hour 15 minutes:
<cfquery name="myquery" datasource="mydsn" cachedwithin="#createTimespan(0,1,15,0)#">

Preventing Known Memory 'Leaks'

Specify CFFunction Output Attribute

For any <cffunction> and <cfcomponent> tags, make sure that you have output="false" specified. If for some reason you do need output from the function, be sure to explicitly add the output="true" attribute. There is a bug in CF that leaks memory when the output function is left of function and component declarations.

Use Var Scope for Variables within CFFunction

Make sure all functions have their variables in the "var" scope, including queries. The varscoper utility here will check your code for any missing var statements in your code: http://varscoper.riaforge.org/ We highly recommend using this on a regular basis for all your sites.

Handle Bots and Spiders Properly

Because bots and spiders can create a lot of useless sessions when indexing sites, we recommend setting a custom session timeout as shown here: Lower Session Timeouts for Bots and Spiders

Debugging Individual Scripts

During non-peak hours for your site, try enabling the ColdFusion debug output and adding your IP to the remote debug IP list. Then load the most frequently accessed pages and grab the debug output. Once you have this, focus on improving the slowest sections of code first.

Additionally, if you have Seefusion on your VPS, it will hightlight the server's slowest scripts. You can also obtain stack traces of running scripts to find the root cause of any slowness.
More info: Using SeeFusion to Monitor ColdFusion Performance on a VPS/Dedicated_Server

NOTE: This section primarily applies to VPS/Dedicated customers only. We do not allow debugging on our shared ColdFusion servers, as it negatively impacts server performance. Also, Seefusion is not available to our shared hosting customers.

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