What are the risks of increasing the "Maximum Output Buffer size"

Question

I'm dealing with a migration from ColdFusion 9 to ColdFusion 11. One issue I've run into is essentially the same as that detailed in this question: cf10 unable to add text to HTML Head

The root cause in my case is a particular page that weighs in at about 3 MB, which is bigger than the output buffer (which is at the default 1024 KB), and is causing CF to flush the cache. This in turn breaks a call to cfhtmlhead in OnRequestEnd().

Redesigning the page is not a practical solution right now. (Maybe in the future.) My problem is "solved" by increasing the "Maximum Output Buffer Size" to 4096 KB.

What are the risks to increasing this value? There are other apps/sites on this server. Could there be memory issues? Performance degradation? (Trying to find a reference for this has been frustrating.)

The ColdFusion 11 Lockdown Guide says:

A lower output buffer size may reduce the memory footprint in some applications.

The server and JVM would seem to have plenty of memory.

---

Since there seems to be some confusion about which setting:

Uncloak

Is that the actual name of the setting (Maximum Output Buffer size)? – Ostosis

Yes. It's right there on the CFAdmin Settings page. – Uncloak

I don't see it in my admin (ColdFusion 9.0.1). I found reference to it in the lockdown guide as you mentioned. But I can't find it in the online documentation for the settings page either. ???? ColdFusion 10 ColdFusion 11 – Ostosis

I did check Enterprise version. I don't see it. ?? – Ostosis

I added a screen shot – Uncloak

I am not sure of the following but it might be helpful: If the maximum memory usage is 4096 kb for each request, then the maximum memory usage might be maximum number of simultaneous templates requests 25 * 4096 kb = 100 Mb. Again I must emphasize that i am not a 100% sure of the above. – Land

I'll add, for those interested, that the Admin setting referred to above was indeed new for CF10. That's why some report not seeing it in their CF9 Admins (and it was not mentioned in the CF9 Lockdown guide, for the same reason). That said, It's not clear if perhaps it was a setting that was there under the covers (an xml or property config file) in 9 and earlier and only now exposed. It's also therefore not clear if it may have had a different default in 9, or one may have had it set lower (through tweaking) on 9, and might hit a problem with a new install's default of 1024. Hope that helps. – Breastsummer

Answer 1

Increasing the output buffer will simple allow the server to consume more memory per request. Having a cap prevents the template engine from dealing with an unexpected high number of dynamic includes and filling up the server's memory.

It's safe to increase on the same level it's safe to have a single request that outputs 3 MB of data. ;)

Sheathing