Caching in Tatin

When a Tatin package and its dependencies are installed or loaded, it seems to be a good idea to save those packages in a machine-specific cache because obviously when the package is requested again, be it by the same user but for a different purpose or a different user, downloading should be avoided because it's already saved on the machine.

And that's exactly what Tatin does by default, with two exceptions:

1. Packages that are betas are never cached.

   The goal is to not clutter the cache with short-lived beta versions.

2. In case a server operates an “Any” delete policy, no packages of that registry will be cached.

   Once a package got deleted it should not be available anymore, neither from the registry itself nor from the cache.

   Note that we advise operating a “none” or “Betas-only” policy on non-local Tatin servers.

Caching can be influenced by setting particular parameters in ⎕SE.Tatin.MyUserSettings, an instance of the UserSettings class, but also by setting particular parameters in the registries saved in the user settings.

These parameters allow you to…

• define the folder that hosts the cached packages
• toggle caching on a global level
• disable caching for particular registries

Note that disabling caching in either way means that packages are neither written to nor read from the cache.

These parameters have global scope: they affect all registries.

This is a Boolean that defaults to 1. Settings this to 0 means no caching takes place: no reading from the cache, and no writing to the cache.

There is no default, meaning that the folder that hosts cached packages depends on the operating system.

The function GetPathToPackageCache returns either the value of MyUserSettings.path2cache or the OS-specific default path if path2cache is empty.

This property's main purpose is to allow test cases using a temp folder: the tests should not temper with the default cache.

Adding a registry to the user settings requires…

• creating an instance of the Define Registry class
• amended the properties of that instance
• add the instance with the Add method to MyUserSettings

One of the parameters of an instance of DefineRegistry is noCaching. This is a Boolean that defaults to 0, meaning that packages from that registry will be cached unless caching is switched off on a global level via MyUserSettings.caching.

If it is 1 instead then packages from that registry will never be cached.

This is typically used when you have a local Tatin Server running, and you are fiddling with packages managed by that server.

The user command ]Tatin.Cache helps manage the cache. It can be used to list the contents of the cache as well as to clear the cache.

Enter ]Tatin.Cache -?? for details.