Investigate feasibility of streamer file/data format based fix

[makortel]

Conceptual ideas were listed in cms-sw/cmssw#44643 (comment)

[makortel]

Currently working on a more concrete plan of option 2

[makortel]

Latest comments in the issue suggest going with option 1 instead

[makortel]

Design session on option 1

• Easy way: Source would issue a file transition when it encounters a "SendProcess" section in the concatenated streamer file that differers from the previous "SendProcess" section
  • Or only when it encounters a new "SendProcess"?
    • In this case the Source would have to tell BranchIDListsHelper what to do when the "SendProcess" differs from the previous one
• Plan
  • Add new section "SendProcess" (need better name)
    • Need to change streamer writer and reader
    • But don't use them yet at this stage (i.e. content is dummy)
  • "SendProcess" (either file or data format) would contain the checksum of the corresponding InitMessage, and do sanity check early
    • I.e. no need for Add SendJobHeader checksum to SendEvent, and a sanity check to streamer source #881 anymore
  • Source monitors changes in the "SendProcess" content (checksum), and initiates a file transition when "SendProcess" differs from the previous
  • Move the BranchIDLists from SendJob to "SendProcess"
  • Try to avoid file transitions when "SendProcess" differs from previous, but has been seen before in the process
  • Try to avoid file transitions altogether
    • Needs Allow BranchIDLists to be used and updated concurrently #882

[makortel]

I formalized the plan to #873, and consider this investigation task complete