Client Side Session Management€¦


Ok this is an old hobby horse I’ve reeled out many times, and now that I’ve got round to starting a blog what better place to find a permanent home for this old equidae.

The traditional way of managing sessions is on the server with the application container managing session keys/data. As a front end developer your job is simply to populate the session data as it is capatured on screen, the application container does the rest for you.

The application container should offer different mechanisms for replicating session data across servers, thus providing session failover. It should also optimise the storage of the data itself, and manage the session keys with it’s own policies for clearing out dead sessions.

The problem with this model is that it is simply not that easy. Some of the issues that need further consideration are: Memory optimisation, Long vs Short Running sessions, Server Redundancy:

When storing data in sessions, the data element is normally given a name, generally this is something meaningful that a developer can use to make code more readable. However these name themselve take up memory.

Whilst this may not seem a huge issue with the amount of memory in servers these days, we’ll see later in the post why optimising memory for sessions is necessary. So one improvment you can make is to implement hashing to reduce lengths of names used in code. Another technique would be to use compression for the actual session data especially for large free text fields.

Generally there are two types of sessions long running or short sessions. Typically internal applications such as call centres will have users that log-in in the morning use an application all day, and log-off at the end of the day.

Such applications if not designed efficiently often do not release session data during the session, this can have the issue of builiding up huge memory requirements per user of the application. Prior to memory depletion, performance degradation will be the first issue as memory is swapped in/out of disk, followed by out of memory server crashes. Hence developers need to consider what memory should be held and when to release this memory.

Short running sessions with mass users e.g. shopping sites, tend to have less per user storage requirements but many more users, creating a large memory requirement overall. In this scenario identifying dead sessions is paramount to reduce memory redundancy. Other optimisations include identifying session data that is used not per user but globally across all sessions, and caching one instance of that data rather than load it per user.

So it is for reasons like the above why client side session handling make so much sense, if only it was supported as standard by the browser rather than having to use hidden fields.

Quite simply client side session management is a means of keeping data in the browser rather than on the server, therefore reducing the memory requirements and extra processing that an application container has. It would not only reduce the cost of the server you’d need it would also improve performance of the client application also, more so than the use of Ajax.

I can’t think of any downsides to this approach whilst the upsides are huge. What do you think?

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