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Minos DBI Nick West. Contents The Placeholder Strategy The Services It Provides Short Term Issues Long Term Solutions. The Placeholder Strategy. Why now? Because We have an urgent need to record calibration data, distribute it and make it available to the offline code

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minos dbi nick west

Minos DBINick West

Contents

The Placeholder Strategy

The Services It Provides

Short Term Issues

Long Term Solutions

T2K Collaboration Meeting

the placeholder strategy
The Placeholder Strategy
  • Why now?
  • Because
    • We have an urgent need to record calibration data, distribute it and make it available to the offline code
    • A native solution isn’t due until at least the Summer
  • Won’t it be very wasteful?
    • Have to rewrite all the code and data when the native solution becomes available?
  • No – it will be a good fit
    • In January at UK Meeting at Liverpool Iain Bertram proposed DBI API based on MINOS
    • See pages 10 onwards of his talk
  • Allows placeholder strategy
    • Thin wrapper package: oaOfflineDatabase
    • Implementation package: MinosDBI
      • MINOS DatabaseInterface package + 8 support packages
      • Backend is ROOT's SQL library
  • Low cost migration to native implementation
    • Code should be ~ free
    • Data should be simple 1:1 mapping DB tables and rows

T2K Collaboration Meeting

the services it provides read access concept
The Services It Provides: Read Access: Concept
  • Concept: DB table
    • Individual row has
      • Set of calibration constants for a single "element" (e.g. channel)
      • A "validity" - a date range over which the data is valid
    • Complete DB table contains data
      • For all elements
      • Over extended period (multiple, normally overlapping, validity ranges)
  • Database query
    • For a given “context” i.e. date/time
    • Get "best" rows for all elements
      • "best" because must resolve any overlaps for each individual element

T2K Collaboration Meeting

the services it provides read access code
The Services It Provides: Read Access: Code
  • Example TFB calibration table: DEMO_CALIB_TABLE4 columns: CHANNEL_ID int, I_PARM int, F_PARM float, S_PARM text
  • Must develop corresponding table row class class TDemo_Calib_Table : public TTableRow { public: TTfbChannelId GetId() const; Int_t GetIparm() const { return fIparm; } Float_t GetFparm() const { return fFparm; } string GetSparm() const { return fSparm; } void Print(); ... };
  • The Query: For event context return handle to a vector of TDemo_Calib_Table rowsTND280Event event; ND::TResultSetHandle<ND::TDemo_Calib_Table> rsh(event.GetContext());
  • Sequential Access GetRow(int index) e.g. Iterate over all rowsfor (Int_t irow = 0; irow < rs.GetNumRows(); ++irow) rs.GetRow(irow)->Print();
  • Random Access GetRowByIndex(int index) e.g. For given TFB return corresponding rowND::TTfbChannelId id;const ND::TDemo_Calib_Table* row = rs.GetRowByIndex(id);if ( row ) row->Print();else ND280Log("bother!");

T2K Collaboration Meeting

the services it provides memory management
The Services It Provides: Memory Management
  • TRseultSetHandle is a lightweight handle
    • Can copy, pass by value etc.
  • DBI retains heavyweight result set
    • At least until all handles destroyed
  • Actually longer
    • Consider typical Use CaseLoop over events Request calibration constants for current event Calibrate current event Process current event Delete current event
    • After event deleted no handles remain
      • But there is a very good chance that next event will request the same constants

T2K Collaboration Meeting

the services it provides aggregation natural structuring of data
The Services It Provides:Aggregation: Natural Structuring of Data
  • A result set represents entire detector
    • But detector granular (sub-detectors)
    • No reason why all rows have same validity: some may be more volatile than others
  • Solution: Form “aggregates”
    • All rows sharing a validity are aggregated together
    • First column of row is an integer SEQNO
    • Members of aggregate have same value of SEQNO
  • The SEQNO is primary key to auxillary table that has validity
    • Plus other useful information e.g. insertion time, creation time
    • Saves space, record validity data just once, not with every row of data
    • Saves time, do date query just once (much slower than SEQNO query)
  • For each table map aggregates onto sub-detectors
    • Or onto whatever natural structure the data has
    • O.K., to have one aggregate if no internal structure
    • O.K. to have multiple aggregates per sub-detector if that is what is required
  • The interface hides this structuring
    • For the supplied context it locates all aggregates
    • Presents as single “seamless” table

T2K Collaboration Meeting

the services it provides writer support
The Services It Provides:Writer Support
  • Have not exposed MINOS writer support
  • But the hard bit is getting all the data and assigning a validity
    • Beyond the remit of this talk!
  • The tricky bit is allocate a unique (within table) SEQNO
  • Have provided service for that
    • Can allocate 2 types of SEQNO
      • Local – unique within this database. Use for testing and then recycle
      • Global – unique within all databases. Allows multiple Master databases
  • Quite easy to write data using the unix ‘mysql’ command.

T2K Collaboration Meeting

short term issues table definition and population
Short Term Issues:Table Definition and Population
  • Table Definition: MINOS DBI places some minimal constraints
    • Defines first two columns
    • Remainder can be arbitrary combination of ints, floats and strings (no objects)
    • The calibration group need to finalise table definitions
    • We need to agree how we aggregate sub-detectors for each table
  • Associated TTableRow Class
    • For each table have to write a table row class (subclasses ND::TTableRow)
      • Very simple
      • Holds the data for one row or state derived from it
      • Provides access to this data or services derived from it
      • It is an important interface if want to keep table structure hidden
  • Table Population
    • Determination of constants for each validity interval beyond remit of this talk
    • Once data has been assembled
      • Use interface to allocate SEQNO
      • Write
        • Directly from C++ using ROOT's SQL interface
        • Indirectly to ASCII file and then simple script to write using mysql command

T2K Collaboration Meeting

short term issues data distribution
Short Term Issues:Data Distribution
  • What is our distribution model?
    • I don't know – do we have one?
    • But not one database for entire collaboration
      • Too slow and too fragile
    • Could have single Master feeding a series of Slaves
  • Snag:
    • At least in short term could have data written at multiple sites
      • KEK, Tokai, Liverpool, CERN, Vancouver, ... ?
    • Could even have single table e.g. pedestals written at multiple sites
  • How do we
    • Merge together ?
      • MySQL replication only works for single Master
    • Make available elsewhere ?
  • MINOS have a DB management package (not in T2K repository)
    • Supports up to 9 Masters and arbitrary number of Slaves
    • Incorporates a validation system that verifies distribution
  • As a short term ~ few months operation I could distribute amongst Masters
    • Not make code available, just run operation from Oxford
    • No support for Slaves (use your local Master)
    • For each Master I would require a writer account accessible for Oxford
  • Can only be short term - The solution doesn't scale
    • As tables grow validation from a remote site becomes too slow
    • I am not looking for a maintenance job - I go part time in October!
  • In longer term
    • Need to have a model !
    • It could be a single Master at KEK and then use MySQL replication

T2K Collaboration Meeting

long term solutions native implementation
Long Term Solutions:Native Implementation
  • Must start with an in-depth examination of Use Cases and Requirements covering
    • What types of data?
      • Possiblities: beam spill, slow controls, calibration, book-keeping
      • Each has a different volatility
    • Do we support unsigned integer data?
      • MINOS DBI doesn’t (but did until we tried to support Oracle backend)
    • What defines "Context" besides date and time?
      • Possibilities: run, type (real/MC), sub-detector
    • How do we resolve overlaps to get "best" rows?
    • Do we support local roll-back to reproduce past results?
    • How do we support global roll-back for past recalibration passes?
    • How do we support trial table updates ?
  • Why not continue with the current MINOS DBI?
    • After all if it ain’t broke why fix it?
  • No!
    • It is the solution to MINOS requirements NOT T2K
    • Must start with analysis NOT implementation!
  • What if it is shown to be a good fit to T2K requirements?
    • Should we keep it then?
  • No!
    • Code is far too dirty: drags in 8 other MINOS packages
      • Some could be removed e.g. leak checker
      • Some could be replaced e.g. logger
      • But others are essential e.g. Validity, Registry
    • Has (at least) one serious flaw
      • Creation Date used for two conflicting purposes
    • There could be others
      • Other experiments (SNO+, Daya Bay and Double Chooz) are either using, or actively considering using, the MINOS code
      • I can ask them what else they found.
  • In any case I have not discussed any of this with Iain Bertram
    • I don't know haw far his plans have developed.

T2K Collaboration Meeting