Last night I was online, shopping coincindentally on Cyber Monday, for presents for both my Dad's birthday and my nephew's birthday.
A work colleague happened to catch me online to ask some questions. Now, these answers are not from a book, just what I said right out of my head -- JUST as I would if you and I had this conversation. Here is our Lotus Sametime conversation, verbatim, no editing. updated: one minor edit marked by  -- OK, and I also put in the html tags and made the requester anonymous, of course. So -- sure, I could have said more about the virtues of data sharing and WLM. They are many! Forgive me, it was nighttime and I wasn't in a "marketing" mood.
In any case, please enjoy the truthiness of this exchange.
Dec 1, 2008
8:25:22 PM coworker Hi, do you have time to give me a 101 lesson on db2 z stuff?
8:28:11 PM me right now?
8:28:19 PM coworker yes
8:28:38 PM me what do you need to know?
8:29:07 PM coworker ok here come the stupid questions...
8:29:10 PM what is data sharing?
8:29:58 PM me it's 2 DB2 subsystems that share one set of data, for availability and scaling beyond one machine
8:30:06 PM 2 or more that is
8:31:02 PM coworker ok so that leads me to another question, can you explain subsystems, lpars ? what is it like in windows world?
8:31:46 PM me a subsystem is a DB2 installation
8:32:18 PM an lpar is a "logical partition", kind of like a VM on windows...
8:32:59 PM coworker can you install anything else on a subsytstem?
8:33:12 PM how do subsystems and lpars relate to each other?
8:34:34 PM me a subsystem is just db2's code, it runs in an operating system which is in an LPAR. other programs (like IMS and websphere) can be installed in that same operating system instance in that same LPAR
8:36:49 PM coworker oh oi see, i'm getting confused with the subsystem term to mean a z/OS OS term
8:36:50 PM got it
8:36:57 PM so tell me about hypersockets?
8:37:56 PM me they are a "fast pipe" for TCP/IP between LPARs on a physical z box - like a 1GB network but faster (don't know the exact numbers)
8:39:10 PM coworker so is this DRDA or no?
8:39:15 PM or using db2 connect
8:40:30 PM me DRDA communication messages travel over over TCP/IP, so if both sides are in LPARs, then they can go over the hypersockets - such as Linux on z on one side in an LPAR, and DB2 z on the other side in an LPAR
8:41:27 PM coworker so when 2 lpars communicate they do not use TCp/IP, they use hypersockets
8:41:30 PM is this correct?
8:42:32 PM me they do use TCP/IP, which travels over the hypersockets as a physical path - like a network wire
8:42:53 PM now... 2 datasharing members don't use either, if that's what you're getting at
8:43:12 PM they use the coupling facility to communicate
8:43:21 PM coworker is this built into z/OS or db2?
8:43:26 PM me z/OS
8:43:26 PM coworker the copuling faciloity
8:43:29 PM i see
8:43:50 PM me it's a separate feature of z - parallel sysplex, which is what datasharing is built on
8:44:25 PM coworker how come a customer would want to use data sharing? benefits? cons?
8:45:26 PM me benefits are availability, since all of db2 maintenance can go on one member at a time so they can keep their data available
8:45:49 PM also scalable, since the number of threads to connect to one db2 is limited, the other threads can go to another db2 -- they share all the data
8:45:51 PM coworker o i c
8:46:02 PM ok got it
8:46:08 PM me good!
8:46:13 PM coworker wait one more question hahaha
8:46:15 PM me k
8:46:17 PM coworker tell me about workload mgmt
8:46:22 PM tha'ts a z/OS thing right?
8:47:05 PM me yes - it helps balance when there's more than one subsystem on the LPAR, also helps balance priority between different db2 threads and even helps choose which data sharing subsystem gets a connection based on how busy the systems are
8:47:57 PM coworker how come this is such a big advantage over windows let's say
8:48:06 PM doesn't all operation systems do this
8:48:56 PM me no - windows doesn't let you set the priority of different programs/users/etc (as far as i know)
8:50:52 PM coworker yes you can via task manager
8:50:55 PM although not sure how smart it is
8:51:15 PM what makes z/os workload mgmt so sophisticated
8:51:21 PM i'm just wondering what's the big deal
8:52:28 PM me it's got a pretty complex set of rules and levels of priority, frequent sampling, decaying priority over time, different rules for different times of day, etc. That said, I didn't know it was considered that big of a deal
8:54:30 PM coworkerhahahaha
8:54:36 PM thanks for your db2 z/os 101
8:54:43 PM me any time