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IBM i Database Host Server and the QZDASOINIT Prestart Jobs



Learn more about details concerning the prestart job entry settings for database host server jobs.

Resolving The Problem

The design for the database host server is designed so every connection to the IBM i database host server (as-database service) attaches to a QZDASOINIT prestart job. Beginning with V5R1, the default subsystem for jobs to run in is QUSRWRK. By using the command WRKACTJOB JOB(QZDASOINIT) (and press F14 to include jobs in a program start request wait state), an administrator can see the number of QZDASOINIT jobs that are currently servicing users. These jobs have a status of RUN, DEQW, or TIMW. Jobs that are waiting for new database connections arrive are in a status of PSRW.

Generally, the QUSRWRK subsystem monitor job manages the number of QZDASOINIT jobs that are in a PSRW state in the QUSRWRK subsystem. To view the current settings for the QZDASOINIT prestart job, use the command DSPSBSD SBSD(QUSRWRK) and select Option 10 for Prestart job entries. Then, select Option 5 on the QZDASOINIT program to display the details.

The command CHGPJE SBSD(QUSRWRK) PGM(QSYS/QZDASOINIT) can be used to change parameters. The parameters are:

Initial number of jobs - The number of jobs initially started when the prestart jobs are first started. This value has a default value of 1, which is unrealistically low if you have more than one or two concurrent users.

Threshold - The minimum number of available (in a PSRW state) prestart jobs for a prestart job entry. This value indicates when to start additional jobs. For example, if this value is set to 2 and the number of QZDASOINIT jobs with a status of PSRW falls to 1, the subsystem monitor job starts additional QZDASOINIT jobs. Host server support recommends setting this value to a minimum value of 2.

Additional number of jobs - The additional number of prestart jobs that are started when the number of available prestart jobs drops below the Threshold parameter.

Maximum number of jobs - The maximum number of prestart jobs that can be active at the same time for this entry. By itself, this setting does not prevent additional users from connecting to the DB host server. When the maximum value is reached, the jobs start as evoked batch immediate jobs in the QSERVER subsystem rather than prestart jobs. For more information about limiting the number of host server jobs, see technote How To Limit The Number Of Host Server Jobs (Connections)

Maximum number of uses - The maximum number of sequential uses that can be handled by each prestart job before the job is ended rather than reinitialized. The default is 200. The same job number is used for 200 different connections. If this is set to 1, the job is used one time and then ended after the client disconnects.

You might want to modify these settings to best suit your own needs.  For more information about how to do that refer to document, Tuning Prestart Jobs.

Note: It is possible because of the workload that many prestart jobs could be sitting in a PSRW status. The operating system has a way of dealing with this situation. Every 10 minutes the subsystem compares the number of prestart jobs in a PSRW status with the value in the INLJOBS parameter for that prestart job. If this number is more than double, the INLJOBS parameter then the subsystem ends one-half of the prestart jobs. Because this happens every 10 minutes, the number of prestart jobs in PSRW status eventually goes down to somewhere between the INLJOBS parameter and double the INLJOBS parameter. This cannot be configured by the customer.

Related Information

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Document Information

Modified date:
27 March 2020