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Managing a Database Server


This chapter contains a short guide to administrating database servers under OpenVMS. It also describes how to use the MIMCONTROL command under OpenVMS.

For general information on managing database servers, refer to the Mimer SQL System Management Handbook.

The MIMCONTROL Command

Before you can access a database, the Mimer SQL database server must be started on the node it resides on.

You start, stop and control database servers on OpenVMS using the MIMCONTROL command.

Note: You cannot start the MIMCONTROL program by using the DCL command RUN.

Required Privileges

To use MIMCONTROL you must have either:

or

If the resident memory feature is used (the BPResident parameter in MULTIDEFS.DAT is set), you must have the VMS$MEM_RESIDENT_USER process right.

Database Server Parameters - the MULTIDEFS File

When you start a database server on an OpenVMS machine for the first time, MIMCONTROL will create a MULTIDEFS file containing default parameter values for the database server. These parameters are based on the amount of memory installed on the machine.

You may also generate the MULTIDEFS file manually by using the MIMCONTROL/GENERATE command. For example:

 $ MIMCONTROL/GENERATE TESTDB
 

It is not possible to change the parameters for a running database server.

You can fine-tune database server performance by adjusting the parameters as required.

Refer to the Mimer SQL System Management Handbook for details.

MIMCONTROL Syntax

You run the MIMCONTROL program is using arguments specified on the command-line.

For example:

 $ MIMCONTROL/START TESTDB
 

Starts the database server and provides access to TESTDB.

If you run the MIMCONTROL command without any options it displays help on command-line arguments.

MIMCONTROL Command-line Arguments

For more information on MIMCONTROL arguments and their combinations, see the Mimer SQL System Management Handbook.

Argument
Function
 /STATUS/DCL
Output status information about the specified database server into the symbol MIMER_STATUS for use in a command procedure.
For details about the output string resulting from this option, see MIMCONTROL (/STATUS/DCL).
 /STATUS
Output status information about the specified database server.
 /DISABLE
Disable new user connections to the database server. Users already connected are not affected.
 /ENABLE
Enable new user connections to the database server.
 /KILL
Kill the database server immediately. This should only be used in emergency situations when a normal stop does not work.
The next time the database is started, all databanks that were open at the time the server was killed will be automatically checked. Connected users will receive an error the next time they attempt to access the database.
 /LOGOUT=chan
Force logout of the specified channel number.
Use channel numbers displayed by the USERS option of the MIMINFO command, see the Mimer SQL System Management Guide.
 /START [=timeout]
Start the database server.
If the server does not become operational within the specified number of seconds, the server will be killed.
The default timeout is 600 seconds.
 /STOP [=timeout]
Stop a database server. Any remaining users will be logged out.
If the database server does not stop within the specified number of seconds, the server will be killed.
The default timeout is 120 seconds.
 /WAIT [=timeout]
Wait for all connected users to log out.
If there are still users connected after the timeout period expires, the command fails.
The timeout period should be given in seconds. If no timeout period is specified wait will be performed without any timeout.
 /DUMP
Create a dump directory and produce dumps of all internal database server areas to files in that directory.
The files produced can be examined by using MIMINFO, see the Mimer SQL System Management Guide.
 /GENERATE
Create a new MULTIDEFS.DAT file with default for parameters, if the file is missing.
 database
Specifies the name of the database to access.
If a database name is not specified, the default database will be controlled.
The default database is determined by setting the MIMER_DATABASE logical name.
The DEFAULT setting in SQLHOSTS is not used for MIMCONTROL.

MIMCONTROL (/STATUS/DCL)

The MIMCONTROL/STATUS/DCL command is a special form of the MIMCONTROL/STATUS command which returns the database server status information in the form of a single string containing a comma-separated list which is useful when writing command procedures.

On OpenVMS, the MIMCONTROL command is silent and sets the DCL symbol MIMER_STATUS to the value of the status string.

You can use the lexical function F$ELEMENT() to extract the list elements. For example:

 $ MIMCONTROL/STATUS/DCL
 $ SHOW SYMBOL MIMER_STATUS
 MIMER_STATUS == "Running,Enabled,LOKE_0:[PER.LOKE],0,A2,2008-02-16 
16:10,121323127"
 $ DIR=F$ELEMENT(2,",",MIMER_STATUS)
 $ USERS=F$ELEMENT(3,",",MIMER_STATUS)
 $ PID=F$ELEMENT(4,",",MIMER_STATUS)
 $ SHOW SYMBOL DIR
 DIR = "LOKE_0:[PER.LOKE]"
 $ SHOW SYMBOL USERS
 USERS = "0"
 $ SHOW SYMBOL PID
 PID = "A2"

The MIMTCP Server

If you are using the TCP/IP protocol, a MIMTCP server listening to a specific port (usually port 1360) will be started the first time the database server is started.

TCP/IP Port Number

The TCP/IP port number that the MIMTCP server will listen to is specified in the TCPPort parameter in the MULTIDEFS.DAT file. If several database servers specify the same port number, they will share the same MIMTCP server.

When a client connects to the TCP/IP port, the MIMTCP server will accept the connection. The client specifies the database to which a connection is to be established and the MIMTCP server will hand over the connection to the appropriate database server. All further communication between the client and the database server is then done directly without involving the MIMTCP server.

System Logical Names

Whenever a MIMTCP server starts, it will define the system logical name "MIMTCP_xxxx" (where xxxx is the port number) to be the PID of the MIMTCP server process. This makes it easy to find the MIMTCP server process that is listening to a particular TCP/IP port.

Controlling MIMTCP servers

The command procedure MIMEXE:TCPCONTROL.COM can be used to manage MIMTCP processes. The first parameter given to the procedure controls what the procedure should do. If no parameter is given, a short help message is displayed. The following example shows how the MIMTCP server for port 1360 is stopped and a new server for port 1337 is started:

 $ @mimexe:tcpcontrol
 Usage: TCPCONTROL STATUS        ! Display status for all MIMTCP processes
        TCPCONTROL START  [port] ! Start MIMTCP process for a port
        TCPCONTROL STOP   [port] ! Stop the MIMTCP process for a port
        TCPCONTROL STOP   ALL    ! Stop all running MIMTCP processes
 $ @mimexe:tcpcontrol status
      Pid    Port Version     Username   Started
 00000227    1360    1001B       SYSTEM   25-OCT-2007 22:14:29.22
 $ @mimexe:tcpcontrol stop 1360
 MIMTCP process for port 1360 STOPPED
 $ @mimexe:tcpcontrol start 1337
 Starting MIMTCP process version 1001B
 %RUN-S-PROC_ID, identification of created process is 00004D04
 $ @mimexe:tcpcontrol status
      Pid    Port Version     Username   Started
 00004D04    1337    1001B       SYSTEM   18-NOV-2007 12:09:11.96
 

Starting and stopping MIMTCP servers explicitly using the TCPCONTROL procedure is rarely needed. When the MIMCONTROL/START command is used, a MIMTCP process will be started automatically. This process will normally be active until the machine is shut down. Since the MIMTCP process does not hold any resources, it is not necessary to shut it down explicitly in the machine shutdown procedure.

Using a Memory Resident Buffer Pool

The buffer pool can be created in two different ways. If the MULTIDEFS.DAT parameter BPResident is left blank (the default) the buffer pool is allocated in normal process memory and is backed by the paging file. This means that the buffer pool is subject to normal virtual memory paging; if the system memory requirements increases the operating system may page out parts of the buffer pool.

Since the paging file is used as backing store the paging file quota of the database server process is increased to a suitable value. The working set quotas are also increased. These quotas are ultimately limited by the system parameter WSMAX, so when a large buffer pool is created with this method the WSMAX parameter must be increased accordingly.

At database server startup, the WSMAX parameter is checked. If it is insufficient an error message is displayed with the required value.

If the BPResident parameter specifies a name, the buffer pool is allocated as a memory resident area, i.e. physical memory in the machine is reserved. This has several advantages:

The name that BPResident specifies will be use to name the memory resident global section. Please note that it is case sensitive. The name must be unique (the same section can not be used by two different database servers).

The user that starts a server using a resident memory area must have the process right VMS$MEM_RESIDENT_USER. This can be granted to a user by using AUTHORIZE:

 $ SET DEF SYS$SYSTEM
 $ MCR AUTHORIZE
 UAF> GRANT/IDENTIFIER VMS$MEM_RESIDENT_USER SMITH
 %UAF-I-GRANTMSG, identifier VMS$MEM_RESIDENT_USER granted to SMITH
 UAF> EXIT
 

It is also possible to create a resident memory reservation so that the VMS system puts aside resident memory for the buffer pool at system boot time. By doing this and then running AUTOGEN, the VMS system can be appropriately tuned. This is described in the VMS document System Manager Manual Vol 2, section 3.11 Reserved Memory Registry. The name used in the registration must match the name used in the BPResident parameter.

The maximum supported buffer pool size is 16 GBytes.

Determining Buffer Pool Size

The buffer pool size is calculated by the MIMCONTROL/STATUS command. This command reads the parameter configuration in the MULTIDEFS.DAT file and calculates the required buffer pool size. The size is displayed in KBytes or MBytes and is rounded upwards so the value can be used for a resident memory reservation.

To see the exact buffer pool size, use the MIMCONTROL/STATUS/DCL command. The last value returned in the MIMER_STATUS symbol is the buffer pool size in bytes.

Process Quotas for the Database Server

When MIMCONTROL/START is used to start a database server process quotas are calculated according to the MULTIDEFS.DAT parameter file.

The size of the database server is calculated. The size includes communication areas (70K per User as specified in MULTIDEFS.DAT), thread stacks, local data, initial SQL Pool (SQLPool parameter) and code. If BPResident is not specified, the buffer pool size is also included.

The WSDEFAULT and WSQUOTA (working set quotas) of the server process is set to the calculated server size.

The PGFLQUOTA (page file quota) is set to the calculated server size plus the size the SQL pool can grow to according to the MULTIDEFS.DAT parameter MaxSQLPool. This means that the MaxSQLPool parameter can be used to control the paging file quota for the process.

The WSEXTENT quota is set to the WSMAX system parameter.

Troubleshooting Tips

In order to successfully start a database server, the following conditions must be fulfilled:


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