“Concurrent users” and performance tests

-- Jörg Hoh

A few years ago when I was still working in application management of a large website we often had the case, that the system was reported to be slow. Whenever we looked into the system with our tooling we did not found anything useful, and we weren’t able to explain this slowness. We had logs which confirmed the slowness, but no apparent reason for it. Sadly the definition of performance metrics was just … well, forgotten. (I once saw the performance requirement section in the huge functional specification doc: 3 sentences vs 200 pages of other requirements.)

It was a pretty large system and rumors reported, that it was some of the biggest installations of this application. So we approached the vendor and asked how many parallel users are supported on the system. Their standard answer “30″ (btw: that’s still the number on their website, although they have rewritten the software from scratch since then) wasn’t that satisfying, because they didn’t provide any way to actually measure this value on the production system.

The situation improved then a bit, got worse again, improved, … and so on. We had some escalations in the meantime and also ran over months in task force mode to fight this and other performance problems. Until I finally got mad, because we weren’t able to actually measure the how the system was used. Then I started to define the meaning of “concurrent users” for myself: “2 users are considered concurrent users, when for each one a request is logged in the same timeframe of 15 minutes”. I wrote a small perl script, which ran through the web server logs and calculated these numbers for me. As a result I had 4 numbers of concurrent users per hour. By far not exact, but reasonable to an extent, that we had some numbers.

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Read the complete post at the Things on a Content Management System.

Author server says Loading; for a long, long, long time

- Sensei Martin

When the Author server restarts, it can look, to the users, like it is hanging because as soon as they click on a node in the left hand nav tree they see "Loading" in the central pane. It just sits there saying "Loading" for a long, long, long time.

This can be caused by having lots of old Workflow instances hanging around (check /etc/workflow/instances). In which case, you should ensure that you install the Workflow purge tool from Adobe.

The purge tool by default will clear out any Workflow instances which are less than 14 days old (well the version I have says > 1 day but the code was actually > 14 days). It can be configured to only purge COMPELTED workflow, or ALL of them. However, beware that the default configuration (in my version 1.6.1 anyway) will only purge the following workflow models :-

  • "/etc/workflow/models/dam/dam_asset_syncer_and"
  • "/etc/workflow/models/dam/update_asset"
  • "/etc/workflow/models/dam/delete_asset"
  • "/etc/workflow/models/dam/delete_dam_asset"

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Read the complete post at the My Day CQ blog.

CQ 5.5: Changes to the startup

- Jörg Hoh

See here for the major changes brought with this release.

Amongst the hundreds of new features I would like to point out a single one, which is probably the most intersting features for admins and operation people.

With CQ 5.5 the quickstart does no longer start a servlet engine with 2 webapplications deployed in it (crx.war for the CRX and launchpad.war for the OSGI container including Sling and CQ5 itself). But as now CRX has been adapted work inside an OSGI container it is possible to drop the artifical differentiation between CRX and the other parts of the system, but handle them alike inside Apache Felix. The same applies to the CQSE servlet engine; it’s now an service embedded into OSGI (so the server.log file is gone). So the quickstart starts the Felix OSGI container which then takes care of starting the repository services, the servlet engine and all other services introduced by Sling and CQ5. This streamlined the startup process a lot. And — finally — there is only 1 place where you need to change the admin password.

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Read the complete post on the Things on a content management system blog.

Improving performance with browser caching

- Sensei Martin

On requests, check that you are using browser caching.

Last-Modified should be set.

Expires should be set (seems to be dynamically set if max-age is set on cache-control). On cache-control - watch out for must-revalidate - this seems to bypass the cache.

This is not good:- Cache-Control max-age=0

This is OK:- Cache-Control max-age=1800, public, must-revalidate

NB, public is to allow caching on SSL links.

This is BEST:- Cache-Control max-age=18000, public

Are the flash files cached?

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Read the original blog post at this URL.