IDMS

We have customers that use ASG-PREALRT and ASG-FASTACCESS.
Does IDMS R19.0 perhaps have similar functionality already 'built in' ?

Or are there any other equivalent features or CA-products that could replace them ?

thanks very much for your input.

Regards,

Peter de Wolf (NL)

Hi Peter,

   I am not familiar with PreAlert so don't know all it does.  IDMS has PERFORMANCE MONITOR which probably covers some of the PreAlert functions but not all.

   FastAccess is lookahead buffering as far as I know and IDMS has had PREFETCH for decades.

https://docops.ca.com/ca-idms/19/en/administrating/administrating-ca-idms-database/buffer-management/using-chained-reads 

CA have Performance monitor. It is a good product though it lacks the alerting features that Prealert has. Also, it is still an extra cost product I believe. You could also look at the CMMT/XOMT monitor that John Fisher (Fishman) maintains on this site. The price is right (free), but it too lacks the alerting features of Prealert.

IDMS comes with Prefetch and QSAM that can be used to speed up sequential database access, though there is more control with Fast Access. I do wonder though, what with today's faster machines with more memory and modern DASD, whether Fast Access really makes that much differences these days. Certainly it the past it made a huge difference but is that still the case? If anyone has done some recent bench marking I'd be interested the hear the results.

Ditto...my experience tells me that a good RAID array will perform extremely well.  There may be some benefit to starting simultaneous asynchronous IOs in z/OS.  If there are multiple IO paths you might be able to get more concurrent channel flow but I am guessing not significant enough to matter to most sites.

IDMS QSAM - works really well for area sweeps.  You can just turn it on and it will automatically do QSAM for the first area accessed by the run-unit.  If your first DML statement is for a record in a different area, you will need to supply control cards, however, really easy to use.

IDMS Prefetch - if you are just doing area sweeps with no random access - use QSAM instead.  For random access it takes some tinkering to get the prefetch done right.  You may need to experiment with buffer sizes and when prefetch kicks in for the different areas.  It is easy to unintentionally do prefetch for records that should be random access and you pay the price. 

Large buffers - Buffers are done by specifying the buffer size for a file, and the buffer is expanded for all files within that buffer.  There are limits, too large buffers and it appears performance will suffer when you do not get high enough a hit-rate.   Large buffers can be used with some success in combination with QSAM and Prefetch.

Fast-Access - Easy to use and very good.  In our testing we found that some workloads, such as unload/reload (most but not all) would be faster with QSAM.  We also had workloads that had area sweeps with random access that were faster with Fats-Access than with any of the other methods listed above.

I found that about 2% of the jobs that used Fast-Access were negatively impacted by switching to IDMS QSAM, but I could not pin-point the reason for that impact - but it was between 20 and 40%.  At your installation the percentage of jobs impacted will vary as well as how much that impact is, only proper testing will show the full picture.

I did not find any reason to use IDMS Prefetch, although there may be instances where that might perform better.

This post should not be regarded as a recommendation of Fast-Access, QSAM or Prefetch.  Only testing at your site can identify what is best for your situation.

Peter,

One other thought about the alert function in Pre-Alert.  Using a product like auto-ops you can often fill a lot of those needs with.  If you have a paging server you can interface with you can have auto-paging done for things you need to be alerted about keying on existing messages.  You might need to write some code to put additional messages out for things not covered.

One other alternative to Fast Access is Sequential Prefetch from Cogito which is now under Syncsort.  We had used this product successfully for a long time.  It allows full cylinder reads and track writes for local updates including things like the DBL2 step in the database load process.  I was getting some pretty good bang over prefetch and QSAM in retrieval when I last tested, but the disk has continued to evolve over time.  Prefetch does seem to come pretty close now as best I can tell, but the greatest bang for cylinder reads might be small block sizes. 

John

In a previous shop/employer that I worked, the company was reducing costs in the budget by eliminating 3rd party software products - one of them was Fast Access.  In working with the systems analyst direction, the CA PreFetch was used as the replacement for Fast Access - it was tested for longer running batch jobs as well as the reload and print space utilities.  There was the need to define in the SYSIDMS the buffer parameters for at least one/first file within any area(s) the utility(ies) was running against.  In the majority, the run time of the jobs were less than when using the Fast Access product.  In current shop/employer (no Fast Access product), there was a performance issue in which PreFetch was used and it help reduce the job run time from 7 hours to 3 hours.