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ROOT I/O for SQL databases

Learn about SQL, SQL support in ROOT, storing objects in SQL database, TFile interface, class table structure, TSQLFile, examples, common tables, custom streamers, and external access. Explore how it works with practical examples.

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ROOT I/O for SQL databases

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  1. ROOT I/O for SQL databases Sergey Linev, GSI, Germany

  2. What is SQL? • SQL – Structured Query Language • SQL is language to create, modify and retrieve data from Relational Database Management System (RDBMS) • Standard since 1986, several revisions in 1992 – SQL2, 1999 – SQL3 • Supported in most commercial and open source RDBMS S.Linev ROOT I/O for SQL databases

  3. SQL support in ROOT • Abstract interface via three classes: • TSQLServer – query execution • TSQLResult – result of single SELECT query • TSQLRow – content of single row • Implemented for MySQL, Oracle, PostgreSQL • TTreeSQL class provides TTree interface to database tables. Allow tree drawing and table modifications S.Linev ROOT I/O for SQL databases

  4. Objects store in SQL database • Write code yourself • pro: probably, best performance • contra: development, maintenance • Take existing SQL I/O framework • pro: fast to implement • contra: second I/O scheme for your classes • Convert to binary buffer and write as BLOB • pro: uses ROOT I/O facility • contra: no access to data without ROOT S.Linev ROOT I/O for SQL databases

  5. TFile as interface to database • Main features of TFile: • Subdirectories structure and keys list • Schema evolution • Pro of TFile interface to SQL database: • learning – you do not need to learn • using – same I/O code can be used • developing – code can be tested with standard or xml file format • Contra: • fixed table design • performance S.Linev ROOT I/O for SQL databases

  6. How it works • New TBufferSQL2 class implemented: • inherited from TBuffer class • redefines all virtual methods for basic data types and objects I/O • When writing object: • splits object data on parts, belonging to different class members and produces SQL INSERT queries • When reading object: • generates SELECT queries and extract class member values from obtained tables subset S.Linev ROOT I/O for SQL databases

  7. Class table structure • For each class version separate table • TBox_ver2, TGraph_ver4 and so on • Class members stored in separate columns: • basic data types • fixed-size array of basic types • object, pointer on object (object id) • parent class (version) • special treatment for TObject and TString • Anything else will be stored in “raw” format in special table like TGraph_streamer_ver4 S.Linev ROOT I/O for SQL databases

  8. TSQLFile class • Inherited from TFile • Full support of schema evolution • Beside TTree all other ROOT classes are supported • Additional configuration possible for: • usage of table indexes • transactions • MySQL table types selection • suffixes for column names S.Linev ROOT I/O for SQL databases

  9. Example with simple class class TBox: public TObject, public TAttLine, public TAttFill { Double_t fX1; Double_t fY1; Double_t fX2; Double_t fY2; ClassDef(TBox, 2); }; { TSQLFile f(“mysql://host.domain/test”, “create”,”user”,”pass”); for (int n=1;n<=10;n++) { TBox* b = new TBox(n,n*2,n*3,n*4); b->Write(Form(“box%d”,n)); } } SELECT * FROM TBox_ver2 TObject_ver1 Created tables: • TBox_ver2 • TObject_ver1 • TAttLine_ver1 • TAttFill_ver2 • KeysTable • ObjectsTable • Configurations S.Linev ROOT I/O for SQL databases

  10. Common tables • Three common tables • KeysTable – list of all keys in the file • ObjectsTable – list of all objects id • Configurations – TSQLFile config KeysTable ObjectsTable Configurations S.Linev ROOT I/O for SQL databases

  11. More complicated example TGraph_streamer_ver4 { TSQLFile f(“mysql://host.domain/test”, “update”,”user”,”pass”); TGraph* gr = new TGraph(10); for (int n=0;n<10;n++) gr->SetPoint(n, n+1, (n+1)*(n+1)); gr->Write(“gr”); } TGraph_ver4 parent classes NULL pointer TList_streamer_ver5 ObjectsTable S.Linev ROOT I/O for SQL databases

  12. Support of custom streamers • Important, while lot of ROOT and some user classes has custom streamers • Data, produced by custom streamer, directly written to _streamer_ tables like TList_streamer_ver5 • Special case when custom streamer reads data, written by standard I/O • Even in custom streamer user can split data into different columns of “normal” class table S.Linev ROOT I/O for SQL databases

  13. External access to SQL tables • Easy navigation with simple SELECT statements • One raw in table corresponds to one object • Class name and version for each object can be found in ObjectsTable • TSQLFile::MakeSelectQuery() produce SELECT statement, which aggregates data of object from different tables in one S.Linev ROOT I/O for SQL databases

  14. Example with TBox class Query, produced by f->MakeSelectQuery(TBox::Class()): SELECT t1.`obj:id`, t2.UniqueId, t2.Bits, t2.ProcessId, t3.fLineColor, t3.fLineStyle, t3.fLineWidth, t4.fFillColor, t4.fFillStyle, t1.fX1, t1.fY1, t1.fX2, t1.fY2 FROM TBox_ver2 AS t1 LEFT JOIN TObject_ver1 AS t2 USING(`obj:id`) LEFT JOIN TAttLine_ver1 AS t3 USING(`obj:id`) LEFT JOIN TAttFill_ver1 AS t4 USING(`obj:id`) TObject TAttLine TAttFill TBox S.Linev ROOT I/O for SQL databases

  15. SQL I/O performance • Two aspects: • Time and CPU usage on user host • Quality and number of SQL statements // TFile f(“test.root”,”recreate”); // TXMLFile f(“test.xml”,”recreate”); TSQLFile f(“mysql://host.domain/test”, “recreate”,”user”,”pass”); TClonesArray clones("TBox", 10000); for(int n=0;n<10000;n++) new (clones[n]) TBox(n+1,n+2,n+3,n+4); clones.Write("clones0", TObject::kSingleKey); gBenchmark->Start(“Write"); clones.Write("clones",TObject::kSingleKey); gBenchmark->Show(“Write"); // TFile f(“test.root”,”recreate”); // TXMLFile f(“test.xml”,”recreate”); TSQLFile f(“mysql://host.domain/test”, “read”,”user”,”pass”); TClonesArray* clon = 0, *clon0 = 0; f.GetObject("clones0", clon0); gBenchmark->Start(“Read"); f.GetObject("clones", clon); gBenchmark->Show(“Read"); S.Linev ROOT I/O for SQL databases

  16. Performance measurement * MySQL 4.1 on Fedora Core 4. Pure text queries are used. With ODBC or native MySQL++ client factor 2 to 3 can be gained ** Query text length was limited to 50 KB and long queries were split *** Oracle 10g on SuSE 8. New TSQLStatement class (not yet in ROOT) was used to gain factor 25 in writing compare to standard ROOT S.Linev ROOT I/O for SQL databases

  17. Conclusion • new TSQLFile provides new possibilities for usage of SQL database in ROOT • Tested with MySQL 4 and Oracle 10, can be adopted for other RDBMS • To be done: • enhancement of ROOT TSQLServer classes • new TSQLStatement class is required • investigation of ODBC usage in ROOT • performance optimization S.Linev ROOT I/O for SQL databases

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