CLAYTON@XRT.UPENN.EDU ("Clayton, Paul D.") (07/04/88)
Michael Zehr has asked a question regarding the use of shared RMS files on a VMS system and how to accomplish it. It was part of an answer on shared images. You do not want to INSTALL a data file in orer to have it shared among users on the same processor, or members of the same VAXCluster. What you DO want to have is the following: 1. Have the GLOBAL BUFFER count, which can be shown by doing a $DIR/FULL of the file set to a NON-ZERO value. This value can be set/changed by the DCL command '$SET FILE/GLOBAL_BUFFER=x yyy'. Where x is the number of global buffers to have and yyy is the file that is to have them when its opened. This can be changed anytime the file is not open. Depending on bucket size, and other items, global buffer counts from 5 to 100 (or more) are not unusual. 2. Enough GLOBAL SECTIONS free on the system in order for VMS to map a system global section for it. To see if enough sections are free invoke the INSTALL utility and do the SHOW/GLOBAL command. The bottom of the resulting display will tell you how many sections are still free. VMS needs one section PER file that has global buffers defined PER processor that has the file open. You may want to increase the SYSGEN parameter GBLSECTIONS, and then reboot the system for it to take effect. You can also verify how many RMS files ARE using global buffers while you are in the INSTALL utility. When the SHOW/GLOBAL command is entered, all the global sections with the prefix of "RMS" are for files being shared among users. 3. Enough free pages in the PRIMARY page file in order to provide a backing store for the global section. VMS 4.x systems must use the primary paging file, and not enough space available can reduce the number of buffers that are used to store data in. It is a VERY good idea to have a large 2nd, and/or 3rd page file installed, thus leaving the primary page file relatively free for shared files. The creation and installation of page files can be done at any time. There is a need to have the SYSGEN parameter PAGFILCNT set to the max. number of page files that can installed in the system at any one time. I recommend that both PAGFILCNT and SWPFILCNT be set to '5' or '10' in order to let you add appropiate files as they are needed should the user load drasticly change on you. A reboot is needed for this parameter to take effect. 4. The SYSGEN parameter GBLPAGFIL should be set to the same size as the primary page file. DO NOT SET IT LARGER. This parameter tells the system how much of the primary page file it can use for global buffer sharing. You have to reboot for this parameter to take effect. 5. Then the user has to OPEN the file shared for it to be truly shared among the users with the buffers holding the data only created once. There is NOTHING extra that has to be done for other nodes in a VAXCluster to also have the file opened shared on their processor. VMS will create a global section, and what ever locks are needed, on each processor that has the file open. VMS will also cooridinate the data in the buffers between processors in a VAXCluster. This is where the Distributated Lock Manager lives and works. Who said sharing files only involved opening them shared!! :-) pdc Paul D. Clayton Address - CLAYTON%XRT@CIS.UPENN.EDU Disclaimer: All thoughts and statements here are my own and NOT those of my employer, and are also not based on, or contain, restricted information.