VSAM buffering

milind suman · New User Joined: 19 Aug 2009 Posts: 55 Location: Pune

Hi,
I have a problem in understanding how buffering works for VSAM files.

I created a VSAM ESDS file for logging purpose. Each time, when a CICS program is executed i add 15 records to this file. But, when i execute the transaction multiple times, recent additions are not visible immediately unless until i close the file explicitly?

Can you please let me know the reason for this?
Is there any way to write the records instantly in the ESDS file ?

Thanks for your help

Bill Woodger · Posted: Mon Aug 06, 2012 7:16 pm

Pretty much like any buffering.

Until a buffer is full (for writing) there will definitely be no physical write to the storage media.

Close will ensure that all buffer(s) remaining are written.

If the write was immediate, there would be no point in having the buffer.

Bill O'Boyle · Posted: Mon Aug 06, 2012 7:28 pm

If the time-period allowed between writing all 15 ESDS records independently meets your needs, you could stack these records in a TSQ and automatically write all items to an ESDS using the MASSINSERT keyword when you see fit, which reduces the EXCP's significantly.

You have to close the ESDS file and re-open it to view the contents in Batch written by CICS, updating the High RBA in the catalog.

milind suman · New User Joined: 19 Aug 2009 Posts: 55 Location: Pune

My log file is being used by online transaction , If i Open/close the file to flush the buffer the transaction may abend during file close time .
Is there any way to commit the buffer data into file without closing and opening it .

Thanks for your help .

Robert Sample · Posted: Wed Aug 08, 2012 7:20 pm

The whole point of a buffer is to improve I/O and not have the CPU waiting for the I/O device so much. Your best bet would be to discuss your application design and problems with your CICS support group (person). There are ways around your issue, but they can have negative consequences to the CICS region as well as the LPAR it runs in.

The primary question that hasn't been asked, or answered, yet is why is it so important to you that the data be written to the file immediately? As long as the data gets there eventually, why do you care when it is written to the file?

dbzTHEdinosauer · Posted: Wed Aug 08, 2012 7:40 pm

milind suman · New User Joined: 19 Aug 2009 Posts: 55 Location: Pune

We have to read the log file every 30 minutes to create the transaction report . Journaling in CICS is a solution instead of logging for this case ?

dick scherrer · Posted: Wed Aug 08, 2012 10:13 pm

Hello,

Robert Sample · Posted: Wed Aug 08, 2012 10:28 pm

Why do you need a transaction report every 30 minutes? This sounds like some VERY inexperienced people coming up with "requirements" that they would like without realizing the impact.

Using journal writes will provide you what you want, as long as you use synchronous mode -- asynchronous puts you right back where you are now with the VSAM writes. However, be aware that using synchronous journal writes WILL impact the application performance as well as the CICS overall performance.

dbzTHEdinosauer · Posted: Wed Aug 08, 2012 10:31 pm

well, as Mr Scherrer so aptly stated,
WTF does someone need a report every 30 min?

that said,
since the analysis is done in batch,
yes journal,
which allows you to flip between journal files,
thus no interruption in the online activity.

but then again, if some idiot wants a report every 30 minutes,
why not make the generation of the report a cics screen,
which would mean you can keep the esds file
(an all the code that populates the file)
in place.

the only thing that you would have to write is the online screen,
which could have an option to generate hard copy of something,
if it was really needed.

what i would do, is create a web app, so the clown could look at a graph.

Bill O'Boyle · Posted: Wed Aug 08, 2012 10:54 pm

You could utilize an A/B log-file method, using ENQ/DEQ and the ability to store the active log-file suffix (A/B) in an area which can be accessed and ENQ'd/DEQ'd by all CICS resources, such as a CWA.

Define a transaction, which kicks off every 30 minutes, ENQ's on the current active log-file, switches it (A to B or vice-versa), DEQ's on the now inactive file, closes and reopens this file and then another task can read all the records. Also, ensure the new-active file is ENA, so that it opens upon first usage, using (for example) SET FILE(FILENAME) DELETE to clear it beforehand. Ensure your ESDS log-files are defined with the REUSE attribute.

Within the ENQ/DEQ scope, if an ENQ is entered by the background task and another CICS task/program is trying to write to this log-file (ENQBUSY is raised), ensure that after the ENQBUSY is completed in the background task, the file-name suffix is obtained from the shared-area by the CICS task/program which had been waiting.

Serial usage is the key to getting this to work properly (ENQ/DEQ).

Note: Once a background task has completed reading the file, the file needs to be cleared, so when it becomes active again, its first record written will be its initial record. This flip/flop applies to both the A and B file.

You also have the option (and perhaps a wise one at that) to backup this file to another file before clearing it.

Just another method....

milind suman · New User Joined: 19 Aug 2009 Posts: 55 Location: Pune

The requirement is to get the alerts in the form of report for some specific kind of activities by online customers . seems its important for them to get the alerts for some reason which I dont know. Performance is important since its banking transaction . I am not sure what to suggest and do for this requirement

Akatsukami · Posted: Wed Aug 08, 2012 11:58 pm

dbzTHEdinosauer · Posted: Thu Aug 09, 2012 12:01 am

if you have the money,
i have the time,
to make state-of-the-art enhancements to international banking systems.