%SYSTEM-F-MBTOOSML

[David Kramer_2]

In the process of moving from VAX to Alpha (OpenVMS Alpha 7.3-2). Doing process-process communication via mailboxes. In the system service call SYS$CREMBX setting max message size to 4096. I'm getting mailbox too small error trying to pass about an 1100 byte message. Thinking I've probably missed either a sysgen or account parameter (only set this up on VAX a bazillion years ago) which allows this max message size - wondering if someone has ideas on how to troubleshoot.

Thanks in advance for your help

[David Jones_21 · Accepted solution]

Mailboxes have a quota as well as max message size, the defaults are set by sysgen parameters DEFMBXBUFQUO (default 1056) and DEFMBXMXMSG (default 256). Change your $crembx call or DEFMBXBUFQUO (it is a dynamic parameter).

[John Gillings]

See HELP/MESSAGE MBTOOSML below

Mailboxes have both a maximum message size and a buffer quota. Generally the quota should be bigger than the maximum.

As David has noted, the SYSGEN parameters DEFMBXMXMSG and DEFMBXBUFQUO define the default values for the $CREMBX parameters MAXMSG and BUFQUO.

IMHO any call to $CREMBX that depends on the default is incorrect! Depending on site specific SYSGEN parameter values is bad. I'm guessing that your error is just anther case supporting my opinion :-) Make sure you have explicitly set both BUFQUO and MAXMSG appropriate to your application.

$ HELP/MESSAGE MBTOOSML

MBTOOSML, mailbox is too small for request

Facility: SYSTEM, System Services

Explanation: This message can occur under two conditions:

o A write request to a mailbox failed because the message
exceeds the maximum message size specified when the mailbox
was created.

o In a call to $GETQUI or $SNDJBC or upon execution of a
queuing command (such as PRINT, SUBMIT, SHOW ENTRY, or
SHOW QUEUE), your process specifies more than the maximum
allowable number of identifiers.


User Action: Verify that the call is coded correctly. For a mailbox error,
verify the maximum message size specified for the mailbox and
increase the size if necessary. For a queuing error, limit the
number of identifiers to the current maximum.

[Ian Miller.]

The mailbox quota is the limit of how many bytes can be queued in a mailbox. Changing the application as suggested would be best.

If you are working with a program which uses mailboxes then you may find the following free programs of mine useful

MBMON - A progam to copy messages written to a mailbox and display and/or record them for later display
ftp://ftp.process.com/vms-freeware/fileserv/mbmon.zip

MBU - VMS mailbox utility-- show lots of detail about a mailbox, create mailbox, read, write, view messages without reading
ftp://ftp.process.com/vms-freeware/fileserv/mbu.zip

[Brian Reiter]

Just a note:

MBMON is well worth looking at. Helped a lot when tracking down a tricky interaction bug.

[Ian Miller.]

Brian, I'm glad to know someone is using my software :-) Email me at the address included with the software and let me know what you think.