MEMDataBase

• Database to store MEM output values.
• The idea is to calculate the MEM once for each event and store it here with a unique sample, run, lumi, event identifier.
• Then the MEM can be retrived using these identifiers.
• It is important to quickly find the correct event out of O(100M) other events while keeping the memory footprint low.
• For this the database is hierarchically structured according to sample, run, lumi, event. And restructured when adding additional events.
• Because of this creation is somewhat slow.
• There are certainly better database solutions, but i am no specialist and wanted to learn something doing it this way :D

Setup

This is setup as a CMSSW package so you need CMSSW. But the code actually only need ROOT and can be used without CMSSW. Last tested with CMSSW_8_0_19

cd $CMSSW_BASE/src
git clone https://github.com/kit-cn-cms/MEMDataBase.git
scram b 

Usage

The database will be compiled as library which can be importet to python using

import ROOT
ROOT.gSystem.Load("libMEMDataBaseMEMDataBase.so")

Writing

Initialize the Database to a writable path (that already exists)

myDataBase=ROOT.MEMDataBase("/nfs/dust/cms/user/kelmorab/MEDataBase")

Create the top level hierarchy for a specific sample and systematic. Use an unique identifier which CANNOT contain underscores. e.g. ttbarInclusiveJESDOWN

myDataBase.AddSample("ttbarInclusiveJESDOWN")

Similarly for other samples. You can also later add eventsand other samples.
But you can not replace already existing events.

Now add events with identifiers and MEM information

myDataBase.AddEvent( sampleName, run, lumi, event, p, p_sig, p_bkg, p_err_sig, p_err_bkg, n_perm_sig, n_perm_bkg )

Finally save the database

myDataBase.SaveDataBase()

More examples in https://github.com/kit-cn-cms/MEMDataBase/tree/master/MEMDataBase/test

Reading

Initialize database

myDataBase=ROOT.MEMDataBase("/nfs/dust/cms/user/kelmorab/MEDataBase")

Add samples with identifiers

myDataBase.AddSample("ttHbbJESUP","ttHbbJESUP_index.txt")

The index file contains a list of internal files and is created automatically with the name "sample_index.txt" during the write step. Just use the argument like this.

Retrieve MEM

result=myDataBase.GetMEMResult("ttHbbJESUP", run, lumi, event)

result is a simple class https://github.com/kit-cn-cms/MEMDataBase/blob/master/MEMDataBase/interface/DataBaseMEMResult.h
Get MEM p

result.p

More examples in https://github.com/kit-cn-cms/MEMDataBase/tree/master/MEMDataBase/test

Usage in CMSSW C++

You can use the database classes directly in C++ code in CMSSW by calling this class
https://github.com/kit-cn-cms/MEMDataBase/blob/master/MEMDataBase/interface/MEMDataBase.h

Usage without CMSSW

The database only needs ROOT and can be used without CMSSW. For this you need to include the header files and maybe need to change include paths in the database code. Then compile and link as for other custom C++ classes. But usage in CMSSW is the easiest way.