DB2 catalogs: STRNO

DMR-Qualitas Outsourcing

DB2 catalogs: STRNO
Hi folks,

we have opened a PMR to IBM to clarify what STRNO parameter must be
specified at DB2 catalogs. We working with 3 DB2 catalogs, and 2 of them
(created in 1991) has STRNO=2. This parameter was the default in those years
but now default is 3.

At PMR we have received following answer:

DFSMS : Managing Catalogs explains in topic "Specifying the Number of
oncurrent Requests" the parameter STRNO. This is the number of concurrent
read requests for a BCS and can have from 2 to 255. From this manual:
.
Initially define the catalog with STRNO(3). You can monitor the adequacy of
this value by using the Resource Measurement Facility (RMF) to watch for
enqueues on the resource SYSZRPLW.catname, and I/O contention on
catalog volumes. SYSZRPLW is the major name of the resource, and catname
(the name of the catalog) is the minor name. An indication of enqueue
contention is given by the I/O service times, not necessarily the number
and frequency of enqueues on this resource.
.
Seeing reported pmrs, in calalog heavy used, STRNO=3 may be too low and it
is recommeded to set STRNO of 5 - 7. This is also indicated on apar II10752.



At IBM-Main we have posted to find answers and we have encouraged to asking
this question on this forum. Also we have received following comments:

1. STRNO specified in the VSAM Catalog may not be in use. I could be
overridden at open time.
2. The number of concurrent physical I/O's to a DB2 object needs to be
limited espically for reads, this insures that only one copy of a CI is in
the pool at a time.
3. DB2 whenever possible does async I/O that is applications expect to find
the required data in the buffers with out I/O waits. The method for doing
this is called 'PREFETCH' on the read side and 'DEFERED I/O' on the write
side.
4. DB2 has a limited number of prefetch and write engines, usually far fewer
than the total number of objects.

There are 2 different issues here:
1. the MVS catalog that contains the definitions for DB2 utilitized datasets
DB2 does not override anything just issues normal OPEN.
2. the actual DB2 datasets that contain table data and indexes.
DB2 overrides everything for this datasets because it uses media manager
for this IO. DB2 can and does have multiple IO active for the same dataset.
It is handled by DB2 if there are multiple requests for the same block, both
requestors wait for the single IO. DB2 applications wait for the completion
of either async or sync IO (the DB2 terms are PREFETCH and synchronous
read). The only difference is that DB2 will initiate prefetch requests as
soon as the previous IO completed so the data will be available in less
elapsed time.


Could you explain your experience with DB2 catalogs? Which is your STRNO in
DB2 catalogs? And, you have seen SYSZRPLW enqueues? In our installation we
have seen max. of 0.02 enqueue time.


Thanks in advance for your help.

Christian Blesa
DMR-Qualitas

---------------------------------------------------------------------------------
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Avram Friedman

Re: DB2 catalogs: STRNO
(in response to DMR-Qualitas Outsourcing)
I have been following this discussion on the IBM-MAIN listserv and in fact have added a few words to that thread.

From the language quoted in the PMR it is my guess that the question / problem was addressed to DFSMS. If I may be so bold to suggest ... this is a mistake.
The biggest thing that the DB2 Catalog has in common with a VSAM ICF etc Catalog are the letters 'C A T A L O G'. DB2 uses VSAM for DASD management only. It uses Media Manager for physical I/O and it does not use z/OS system service for lock / enqueue serialization of I/O requests.

If you are going to peruse this by way of PMR with IBM I would suggest perusing it with the DB2 team.

Personally I have been around DB2 on OS since before first customer ship and involved with many other data base data communication products like IMS and CICS that do not use operating services for many functions but do there own thing. DB2 not following standard access method rules is neither unusual for DB2 or any other advanced multi user multi address space product. Personally in about 25 years this is the first I have ever heard the suggestion that monitoring STRNO by monitoring SYSZRPLW for the DB2 catalog is indicated. This is supported by the almost total absence of hits on IBMLINK using the keywords 'DB2 STRNO'.

Posting on this list is a good idea. Besides for IBM participation there are many product authors with ISV's, and support people with years of experience who can comment on this.

DMR-Qualitas Outsourcing <[login to unmask email]> wrote:
Hi folks,

we have opened a PMR to IBM to clarify what STRNO parameter must be specified at DB2 catalogs. We working with 3 DB2 catalogs, and 2 of them (created in 1991) has STRNO=2. This parameter was the default in those years but now default is 3.

At PMR we have received following answer:

DFSMS : Managing Catalogs explains in topic "Specifying the Number of oncurrent Requests" the parameter STRNO. This is the number of concurrent read requests for a BCS and can have from 2 to 255. From this manual:
.
Initially define the catalog with STRNO(3). You can monitor the adequacy of this value by using the Resource Measurement Facility (RMF) to watch for enqueues on the resource SYSZRPLW.catname, and I/O contention on
catalog volumes. SYSZRPLW is the major name of the resource, and catname (the name of the catalog) is the minor name. An indication of enqueue contention is given by the I/O service times, not necessarily the number
and frequency of enqueues on this resource.
.
Seeing reported pmrs, in calalog heavy used, STRNO=3 may be too low and it is recommeded to set STRNO of 5 - 7. This is also indicated on apar II10752.



At IBM-Main we have posted to find answers and we have encouraged to asking this question on this forum. Also we have received following comments:

1. STRNO specified in the VSAM Catalog may not be in use. I could be overridden at open time.
2. The number of concurrent physical I/O's to a DB2 object needs to be limited espically for reads, this insures that only one copy of a CI is in the pool at a time.
3. DB2 whenever possible does async I/O that is applications expect to find the required data in the buffers with out I/O waits. The method for doing this is called 'PREFETCH' on the read side and 'DEFERED I/O' on the write side.
4. DB2 has a limited number of prefetch and write engines, usually far fewer than the total number of objects.

There are 2 different issues here:
1. the MVS catalog that contains the definitions for DB2 utilitized datasets DB2 does not override anything just issues normal OPEN.
2. the actual DB2 datasets that contain table data and indexes.
DB2 overrides everything for this datasets because it uses media manager for this IO. DB2 can and does have multiple IO active for the same dataset. It is handled by DB2 if there are multiple requests for the same block, both requestors wait for the single IO. DB2 applications wait for the completion of either async or sync IO (the DB2 terms are PREFETCH and synchronous read). The only difference is that DB2 will initiate prefetch requests as soon as the previous IO completed so the data will be available in less elapsed time.


Could you explain your experience with DB2 catalogs? Which is your STRNO in DB2 catalogs? And, you have seen SYSZRPLW enqueues? In our installation we have seen max. of 0.02 enqueue time.


Thanks in advance for your help.

Christian Blesa
DMR-Qualitas

--------------------------------------------------------------------------------- Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page select "Join or Leave the list". The IDUG DB2-L FAQ is at http://www.idugdb2-l.org. The IDUG List Admins can be reached at [login to unmask email] Find out the latest on IDUG conferences at http://conferences.idug.org/index.cfm



Avram Friedman
(877)311-0480 Voice Mail
[login to unmask email]
Http://www.IBMsysProg.com




---------------------------------------------------------------------------------
Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page select "Join or Leave the list". The IDUG DB2-L FAQ is at http://www.idugdb2-l.org. The IDUG List Admins can be reached at [login to unmask email] Find out the latest on IDUG conferences at http://conferences.idug.org/index.cfm

Avram Friedman

Re: DB2 catalogs: STRNO
(in response to Avram Friedman)
I have been following this discussion on the IBM-MAIN listserv and in fact have added a few words to that thread.

From the language quoted in the PMR it is my guess that the question / problem was addressed to DFSMS. If I may be so bold to suggest ... this is a mistake.
The biggest thing that the DB2 Catalog has in common with a VSAM ICF etc Catalog are the letters 'C A T A L O G'. DB2 uses VSAM for DASD management only. It uses Media Manager for physical I/O and it does not use z/OS system service for lock / enqueue serialization of I/O requests.

If you are going to peruse this by way of PMR with IBM I would suggest perusing it with the DB2 team.

Personally I have been around DB2 on OS since before first customer ship and involved with many other data base data communication products like IMS and CICS that do not use operating services for many functions but do there own thing. DB2 not following standard access method rules is neither unusual for DB2 or any other advanced multi user multi address space product. Personally in about 25 years this is the first I have ever heard the suggestion that monitoring STRNO by monitoring SYSZRPLW for the DB2 catalog is indicated. This is supported by the almost total absence of hits on IBMLINK using the keywords 'DB2 STRNO'.

Posting on this list is a good idea. Besides for IBM participation there are many product authors with ISV's, and support people with years of experience who can comment on this.

DMR-Qualitas Outsourcing <[login to unmask email]> wrote:
Hi folks,

we have opened a PMR to IBM to clarify what STRNO parameter must be specified at DB2 catalogs. We working with 3 DB2 catalogs, and 2 of them (created in 1991) has STRNO=2. This parameter was the default in those years but now default is 3.

At PMR we have received following answer:

DFSMS : Managing Catalogs explains in topic "Specifying the Number of oncurrent Requests" the parameter STRNO. This is the number of concurrent read requests for a BCS and can have from 2 to 255. From this manual:

Initially define the catalog with STRNO(3). You can monitor the adequacy of this value by using the Resource Measurement Facility (RMF) to watch for enqueues on the resource SYSZRPLW.catname, and I/O contention on
catalog volumes. SYSZRPLW is the major name of the resource, and catname (the name of the catalog) is the minor name. An indication of enqueue contention is given by the I/O service times, not necessarily the number
and frequency of enqueues on this resource.

Seeing reported pmrs, in calalog heavy used, STRNO=3 may be too low and it is recommeded to set STRNO of 5 - 7. This is also indicated on apar II10752.



At IBM-Main we have posted to find answers and we have encouraged to asking this question on this forum. Also we have received following comments:

1. STRNO specified in the VSAM Catalog may not be in use. I could be overridden at open time.
2. The number of concurrent physical I/O's to a DB2 object needs to be limited espically for reads, this insures that only one copy of a CI is in the pool at a time.
3. DB2 whenever possible does async I/O that is applications expect to find the required data in the buffers with out I/O waits. The method for doing this is called 'PREFETCH' on the read side and 'DEFERED I/O' on the write side.
4. DB2 has a limited number of prefetch and write engines, usually far fewer than the total number of objects.

There are 2 different issues here:
1. the MVS catalog that contains the definitions for DB2 utilitized datasets DB2 does not override anything just issues normal OPEN.
2. the actual DB2 datasets that contain table data and indexes.
DB2 overrides everything for this datasets because it uses media manager for this IO. DB2 can and does have multiple IO active for the same dataset. It is handled by DB2 if there are multiple requests for the same block, both requestors wait for the single IO. DB2 applications wait for the completion of either async or sync IO (the DB2 terms are PREFETCH and synchronous read). The only difference is that DB2 will initiate prefetch requests as soon as the previous IO completed so the data will be available in less elapsed time.


Could you explain your experience with DB2 catalogs? Which is your STRNO in DB2 catalogs? And, you have seen SYSZRPLW enqueues? In our installation we have seen max. of 0.02 enqueue time.


Thanks in advance for your help.

Christian Blesa
DMR-Qualitas

--------------------------------------------------------------------------------- Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page select "Join or Leave the list". The IDUG DB2-L FAQ is at http://www.idugdb2-l.org. The IDUG List Admins can be reached at [login to unmask email] Find out the latest on IDUG conferences at http://conferences.idug.org/index.cfm



Avram Friedman
(877)311-0480 Voice Mail
[login to unmask email]
Http://www.IBMsysProg.com




---------------------------------------------------------------------------------
Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page select "Join or Leave the list". The IDUG DB2-L FAQ is at http://www.idugdb2-l.org. The IDUG List Admins can be reached at [login to unmask email] Find out the latest on IDUG conferences at http://conferences.idug.org/index.cfm

---------------------------------------------------------------------------------
Welcome to the IDUG DB2-L list. To unsubscribe, go to the archives and home page at http://www.idugdb2-l.org/archives/db2-l.html. From that page select "Join or Leave the list". The IDUG DB2-L FAQ is at http://www.idugdb2-l.org. The IDUG List Admins can be reached at [login to unmask email] Find out the latest on IDUG conferences at http://conferences.idug.org/index.cfm