IBM MQ 9.4.3 for z/OS increases the maximum length of the CONNAME attribute from 48 to 264 characters, bringing the maximum length in-line with other MQ platforms.
This impacts the following channel types:
SDR, SVR, RQSTR, CLUSSDR and CLUSRCVR.
In addition to this change, IBM MQ 9.4.3 for z/OS has optimized how certain channel attributes are stored on page set zero and this change affects all channel types except CLNTCONN channels (see note relating to CLNTCONN channels).
Increasing the length of the CONNAME attribute makes it easier to use a comma separated list of host/port names. Typically, only one hostname is required but you can provide multiple hostnames to configure multiple connections with the same properties. The use of a multiple hostnames may affect the channel start rate, as the connections are usually tried in the order they are specified in the connection list until a connection is successfully established.
Impact to page set zero usage
Previous MQ for z/OS releases including 9.4.0 LTS:
In previous MQ release performance reports, such as MQ for z/OS performance report for “IBM MQ Advanced 9.4 for z/OS”, and MP16 “Capacity Planning and Tuning for IBM MQ for z/OS” there is a section reporting the “PAGESET(0) usage” for MQ objects which includes each of the channel types.
Prior to IBM MQ 9.4.3 for z/OS, it was reported that each of the channel types used 2048 bytes of page set zero storage, or 2 objects could be stored per 4KB page.
These calculations were based on defining 1000 of each type of MQ object and determining the increase in page set zero usage.
Prior to 9.4.3 CD, it was irrelevant whether any of the MQ channels had the minimum number of attributes specified for that channel type or every attribute was configured to the maximum length - in either case, MQ for z/OS could only store 2 channel objects per 4KB page on page set zero.
For example, SDR-type channels where the SENDEXIT attribute is either blank or contains all eight exit names each of eight characters in length, would use the same amount of page set zero storage.
IBM MQ 9.4.3 CD for z/OS:
In MQ 9.4.3 for z/OS, channel objects have been changed to store certain string-type attributes as variable length fields in page set zero as well as supporting the increase in CONNAME length.
If not exploiting the additional characters in the CONNAME attribute, the page set usage for channel type objects will typically decrease, or at worst have the same page set zero usage as prior MQ releases.
In MQ 9.4.3 CD for z/OS, we have changed our measurements to have up to three configurations for each channel type:
- Minimum size of an MQ channel – where the minimum attributes are configured, and any mandatory variable length attributes are configured with short values.
- Maximum size of an MQ channel, using pre-9.4.3 CONNAME length.
- Maximum size of an MQ channel, using 9.4.3’s maximum CONNAME length.
In our measurements, configuration 2 resulted in the MQ channel objects using 2048 bytes or 2 objects per page, matching earlier MQ for z/OS releases.
However, it is unlikely that many channel objects are defined with all string-type characters at maximum length, and as a result we offer the following chart.
The chart shows that for a sender-type (SDR) channel, the maximum number of objects that can be stored in a single 4KB page is 10, and the minimum is 1.
This means that if a sender-type channel is defined with a long CONNAME, for example using the 264 bytes, and all the variable length attributes configured to their maximum lengths, only 1 similarly configured sender channel would be stored per 4KB page.
By contrast a sender-type channel that is configured with the minimum mandatory fields, i.e. example XMITQ and CONNAME only, up to 10 channels could be stored per 4KB page, depending on the length of the values in those attributes.
These channels are based on all channel definitions for a single channel type being defined with the same length attributes and should channel object “one” require more than 2048 bytes and the next object defined require less than 2048 bytes, then both objects may be stored on a single page.
Minimum Objects per 4KB Page:
For a receiver or SVRCONN-type channel, neither of which support CONNAME, a minimum of 2 objects will be stored per 4KB page of page set zero.
For all other channel types, which do support CONNAME, it is possible that 1 object may be stored per 4KB page on page set zero.
Maximum Objects per 4KB Page:
For a sender-type object, a maximum of 10 SDR-type channel objects may be stored on a single 4KB page on page set zero.
For all other channel types, a maximum of 11 channel objects may be stored on a single 4KB page on page set zero.
Note: CLNTCONN channels
CLNTCONN channels on z/OS have not been updated to support a CONNAME of greater than 48 characters in length.
Although CLNTCONN channels can be defined on z/OS, they cannot be exported to a client system because the CSQUTIL MAKECLNT tool used for this purpose was deprecated in IBM MQ 9.1.0 for z/OS.