Networking

Both the server and workgroup products are shipped with the same networking components. So you can upgrade a workgroup engine to a server engine. The client side requestors can connect to either type of engine.

The PSQL Network Services Layer searches for an engine on the network using NetBIOS as well as the other protocols previously supported; Named Pipe, DNS, and NDS. The NetBIOS and DNS protocols can be used to contact a workgroup engine. Server engines on Windows advertise themselves with Named Pipes, so NetBIOS is not needed.

Once the client requestor has found an IP, SPX or NetBEUI address, it will try to establish a connection to a MicroKernel engine using that transfer protocol.

MicroKernel Router Decision Algorithm

The client side MicroKernel router discovers Gateway ownership of files by following a well-established algorithm.

Table 33

Gateway Discovery Priorities

Try to connect to a database engine on the same computer as the data files.

Try to open the data files using the local engine (on the client machine).

Find and connect to the Gateway engine that owns the files.

The first thing the client-side router always tries is to connect to an engine on the same computer as the data. Because of this procedure, it is always more efficient to have an engine running where the data is.

Because the PSQL Network Services Layer uses so many different methods to find and connect to a remote database engine, there may be a time delay on the first attempt to open a file on a file server that does not have a database engine running. If Gateway Durability is turned on, that connection will not be attempted thereafter because the router remembers each machine on which it fails to locate an engine.

If the router cannot connect to an engine on the remote file server, the router then allows the local engine to attempt to open the remote files. The local engine first attempts to create a new locator file and take ownership of the remote directory. If the directory is already owned by another MicroKernel, the local engine returns Status Code 116 to the router.

Finally, the router attempts to discover the Gateway computer. It opens the locator file and reads the name of the Gateway engine. Then it sends the request to that engine. Notice that the router never tries to read a locator file unless it has received Status Code 116 from a MicroKernel first. This behavior means that in order to use the Gateway feature, you must have a local workgroup engine installed. If the attempt to open the remote files with the local engine fails because there is no local engine, the router does not try to read the locator file and no Gateway engine is found.