Introducing Parameter Wednesday – DBM CFG: NUMDB
This is a new blog post format I’m introducing. I’m declaring Wednesday Parameter Day. That means each Wednesday, I’ll pick a parameter and cover it in excruciating detail. Some of the details will come straight out of the info center, but I’ll add my own experiences and insight geared towards e-commerce databases and throw in specifics for WebSphere Commerce from time to time. I’m selecting my own order – they’re not necessarily going to be in the order of where they are listed or alphabetical or even of impact or anything. That also means if you want more details on a parameter, comment or email me and I’ll generally be glad to slip it in. I’m starting with a relatively simple one to get the format worked out.
DB2 Version This Was Written For
Where This Parameter Lives
Database Manager Configuration
Defines the maximum number of databases that can be concurrently active
If this is set too low, you will get an error. May impact how memory is allocated, so shouldn’t be set too high.
8 (Windows server with local and remote clients)
3 (Windows server with local clients)
Recycle Required To Take Effect?
DB2 instance recycle is required for this to take effect.
Can It Be Set To AUTOMATIC?
No, this cannot be set to AUTOMATIC
How To Change It
db2 update dbm cfg using NUMDB N
where N is the number you wish to set NUMDB to
Rule of Thumb
Leave this at the default unless you specifically know you will have more than that number of concurrently active databases.
Since an error message is returned when you need to change this parameter, there isn’t a lot of tuning to be done.
Related Error Messages
SQL1041N The maximum number of concurrent databases have already been started. SQLSTATE=57032
This error indicates that NUMDB needs to be higher.
War Stories From The Real World
This is generally a pretty boring parameter. I’ve seen as many as 14 databases on a single instance. I would generally aim for having fewer than 8 databases on an instance anyway. I’m a big fan of the one database on one instance approach unless we’re talking about small databases like configuration databases or ESB databases. I’ve certainly had to increase the parameter, but there’s nothing complicated about doing that.
Link To Info Center
The info center lists all the parameters that control memory allocated on a per-database basis. See the info center link above to see those links.