Pachyderm: Location Independence

INTRODUCTION

LOCATION
INDEPENDENCE

Many email systems store vital user state on the user's computer. Pachyderm doesn't. All the user's long-term state is kept in the Pachyderm server, accessed on demand by the user over the web. Of course, some transient state resides with the user interface, to make the performance adequate. But the entire system is engineered so that if the user walks away from one client computer and walks up to another, he can continue with his work where he left off.

The most obvious example of this is that the user's messages and associated data are stored on the server, not on the client machine. The client computer never has the "truth" copy of the user's messages, and never holds any form of "lock" on them. In this respect, the Pachyderm protocols are somewhat like IMAP-4 or some usages of Microsoft Exchange Server.

But the most extreme example of this is in message composition. When the user is composing a message, he has a draft window on his screen. The user interface code periodically synchronizes the state of these draft windows with the server. In the simplest cases, this just means that the contents of the draft windows is saved on the server once a minute. But it also means that if the user walks away from a draft window on one client computer, and starts the user interface on another client, this new client will retrieve the saved state from the server and the user can continue with his composition. Further, the first client computer notices that the user has been making updates elsewhere, and retrieves the updated content from the server. From the user's point of view, any client computer he uses has his current composition state readily available.