Access to named/multiple servers for DP4 programs - E4000028 - Revised 07 Jun 2001

From 4.523/4.619 DP4 will support access to named servers from DP4 programs when DP4 TCP/IP networking software is used. Different DP4 programs running on the same client will be able to access different servers. This is a client-side enhancement, upgrading the client programs will allow this enhancement to be used against any 4.520 or later DP4 server. The enhancement is compatible with either the simple client server configuration, or the local resilience configuration, but not with multiple resilience, and is only supported for Windows and Linux/Unix clients. To enable the enhancement you have to do the following:

• Replace the client side programs with the files in the download. Only the core components and PROGRUN are supplied in the download. If you want to use this enhancement with other DP4 utilities let us know and we will send you a pre-release CD ROM.
• Load the client side DP4 network programs as before. This will establish a default server to use for programs that do not make use of this enhancement. This enhancement is compatible with ADCs but the ADCs will need to be relinked with new ADC components first. Contact us if you want to do this.
• Recompile and relink any C programs for which this enhancement is required with the new version of ntown.lib. This will enable a new −server_name server command tail. This will be a standard DP4 command tail analogous to −db from version 4.523/4.619
• When starting the program specify the −server_name server command tail. server must be a pingable name where a DP4 server is running. It is permissible to simultaneously run programs connected to different servers.
• In order to use this facility from ODBC connections you must install the new ODBC drivers package and run instutil −odbc. This will migrate your existing DSNs from "Datafit" to "DP4". You can then use the ODBC configuration dialog to configure the DSN to use a different server from the default server. (Clear the use default server checkbox and specify the server to connect to instead). With the new style DSN the database name is also a configurable property.
• In order to use this facility from programs using the DP4DYN library called the new DP4_OpenNamedConnection() function specifying the name of the server to be used. The DP4 Class library has been updated to add an Open() method that accepts a server name parameter.

Notes

When used with the local resilience configuration the named server is used for remote operations. The −server_name option or its equivalents do not affect which database operations are performed locally and which remotely.

In theory a program can access multiple DP4 servers. In order to do this you have to obtain separate connections to each server. This should be straight-forward for DP4DYN programs. For C programs you need to call srv_connect(), srv_enable() for each server you wish to access (followed by db_open()). You will need to save and restore the values of the df_process and server_handle variables to switch servers. There is no support for two phase commits between servers. If you require such functionality you should use a multiple resilience configuration.

The make_tempname() macro has been replaced with a function. The temporary filenames are different from before. The new scheme will cope with two programs that run against different servers but with the same process number, and will cater for a larger range of process numbers than the previous one (up to 15000, though the limit on number of users is still 416 for the time being).

The IPC between programs and the database manager has changed. All future 4.523/4.619 Win32 enhancements will require the new version of usrlibt.dll to run, but they will run on a 4.520+ system provided this file is installed. For Unix/Linux the programs will require 4.523 srv3/tcp3 to run, but existing applications will run with the new srv3/tcp3 without any problems.

This enhancement is compatible with E4000027, and any common files in the two downloads are identical. In particular you can force SQL to be executed on a particular server by combining the remote=1 flag with a DSN connection to a particular server.

DP4 Version Compatibility

The download for this enhancement is password protected. Please ask us for the password if you would like to use this enhancement.

Downloads

To use this enhancement with version 4.52x rename trmw32o.dll to trmw32.dll. The progrun.exe and ntown.lib are for 4.619, but can be used with release 4.52x for trial purposes. Contact us if you require a proper 4.523 set of components.

21 May 2001 Revised files include later fixes to AUXDISTR/TCPW and enhancement E4000030. Please post SQLERR.PRN to your system database with the 4.5xx version of MAPPOST.