My recommendation has always been to leave Db2/CICS's RLE compression of SMF data enabled even with zEDC compression of the data.
1) Less data will be sent to the zEDC compression engine, which will then process faster. I believe at one point I had an IBM chart that showed this. 2) The data might (likely) compress better because intervening repeated values are removed before it goes through the zEDC compression. (As Andrew shows below.) It might be dependent on the data, but it makes some sense when you realize that LZ77 relies on compressing in 32K blocks and by removing the duplicate zeros you potentially get more interesting repeated data into that 32K block. 3) When the data is read back from the zEDC-compressed store to be sent someplace for processing it will be smaller if the RLE compression was enabled. Depending on what you're doing with the data, that might be significant. 4) The RLE compression is extremely lightweight in terms of CPU. I do not expect it to be noticeable: it's going to disappear in the normal variation in CPU time seen for running the same work on any shared system. The only CICS/Db2s that I would expect could have a measurable increase in CPU would be those that are completely idle and doing nothing but writing interval SMF records to say they haven't processed any data. Scott Chapman On Wed, 17 Apr 2024 16:36:34 +1000, Andrew Rowley <and...@blackhillsoftware.com> wrote: >On 17/04/2024 12:09 pm, Michael Oujesky wrote: >> Yes and zEDC poorly compresses internally RLE compressed records. > >I was surprised how well zEDC compressed the already compressed records. >Using my data: > >zEDC alone : 52000 tracks > >CICS compression + zEDC : 22000 tracks > >zEDC seems to be biased towards speed rather than compression ratio, so >maybe the RLE compression helps by packing more repeated bytes into >whatever compression window zEDC uses? > >> Plus CSRCESRV uses GP engine cycles > >That's true - CPU is probably more expensive than storage, so this could >be just an interesting side-track. On the other hand, I think zEDC has >to decompress and recompress the data for SMF dump etc. so CICS >compression might save some overhead for SMF housekeeping type >operations, reducing the amount of data going through zEDC? > >-- >Andrew Rowley >Black Hill Software > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
