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Database Replication - Distribution

Database Replication - Distribution. Relational public databases. EBI’s mission to provide freely accessible information on the public domain Data formats and technologies, should not contradict to this policy Adopt widely accepted, successful standards that are well known and used

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Database Replication - Distribution

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  1. Database Replication - Distribution

  2. Relational public databases • EBI’s mission to provide freely accessible information on the public domain • Data formats and technologies, should not contradict to this policy • Adopt widely accepted, successful standards that are well known and used • Free access not only in the information content, but in the supporting technologies • Reasonable investment in resources and expertise by users so that the data is accessible to a wider audience • But without a severe restriction to the benefits to the users • A trade-off situation, different users, different needs • Relational databases are an industry standard • Vendors have different implementations but there are underlying formal standards • ANSI-SQL for query expression • ODBC, JDBC for API’s

  3. RDB’s versus flat files • Relational databases are flexible, powerful and consistent • They are a lot more complex • They impose data organisation that can’t be easily vertically partitioned • Organising and inter-exchanging data on a per-entry basis does not come by default • Physical implementations are not standard • Remember the days (or imagine) flat files without a common character encoding standard (without ASCII around) • Vendors support migration of other databases to their own but not the other way-round • There is not a common vendor-independent exchange or dump format • This is not trivial due to differences in implementation details and extensions on the standards

  4. To take advantage of local hardware and CPU time – some operations are simply not possible on-line To avoid continuous dependency on network and EBI resources To extend or merge information with other databases or data sources To utilise the information in new innovative ways To ensure confidentiality of research Why Replicate?

  5. MSD replication options • We offer MSDSD in Oracle • With indexes pre-built • Implementation uses Oracle import-export • With frequent (weekly) incrementals so that new entries are becoming available soon • Users need to have Oracle licence • We have more experience and offer better support • Or in mySQL • In compressed myIsam format without indexes • We give directly the mySQL data-files (they are platform and version independent) • We don’t offer weekly increments but new full releases every few months • We recommend the Oracle distribution for advanced users • But mySQL is great if they can’t afford Oracle • Or want to evaluate the MSDSD database

  6. Database copy on Sun Solaris Schema export-import plus sql-loader files for creating the database initially for Oracle on other platforms Possibility to Import to Non Oracle databases (MySQL) Periodic synchronisation with the MSD master database using periodic incremental scripts for all Oracle platforms Use of two schemas, main search database and incremental Replication Components

  7. Why Incremental Updates Implemented in server side JavaScript Data is exported as Oracle Export files organised in marts Data files on the FTP server Aim for weekly updates Mechanism flexible enough to adapt on different data mart Combinations Prerequisites: Rhino, Java, Oracle-JDBC driver, oracle-export-import The user has just to download and run the periodic incremental import script of a data mart for his database Database version, Data version, Data mart maintenance is controlled via the administration tables through synchronisation Incremental Data Export – Import

  8. Incremental Replication Mechanism DATA MARTS DATA MARTS Increment log Admin Tables Admin Tables JDBC JDBC crontab crontab PERIODIC EXPORT SCRIPT PERIODIC IMPORT SCRIPT Oracle Dump Files Web-FTP Service Target Database MSD Search Database

  9. Replication overview SchemaExport SchemaExport Schema creation SQL scripts Target database Oracle DictionaryJDBC metadata postgreSQL Oracle MSD in Oracle mySQL MSD in mySQL Import Export Configuration INSERTstatements Structure SELECTstatements Source database DataImport DataExport Java serialised data files

  10. JDBC and Java • Java is one of the best environments regarding portability • Java compiled machine code works directly on all platforms • Java serialisation is machine independent • JDBC standard is well defined and detailed • Maps database types to Java object types • Not all implementations are full in all details • JDBC offers metadata services • Easy to get information about schemas, tables and columns through JDBC • Java offers data compression • Implementing a database vendor independent export-import is trivial • Could not find one available so developed a simple and flexible mechanism at MSD

  11. MSD cross-replication • Inputs JDBC metadata and Oracle dictionary • Exports schema creation scripts into SQL files • Gathers information from JDBC metadata and oracle dictionary • Takes care of type implementation details of the various databases (maximum size of varchar etc) • Works with standard ANSI-SQL types only (not object-types, nested tables, blobs etc) • Exports configuration files • Table, column names of target database can be different • Can export subsets of the data • Exports the data in compressed java serialised arrays • In data files or directly piped into the Import mechanism

  12. Cross-replication details • Potentially for any relational database with ANSI-SQL support • Has been tested for PostgreSQL, MS-Access, Mckoi (java RDB) • Flexible configuration • Target tables can be different different • The SELECT and INSERT statements are kept in configuration files • This is how merged (partitioned) tables where built • Includes support for incrementals • This option is still not used in production • The information in the data files can be examined off-line • Foreign keys have to be disabled during the load

  13. Oracle versus mySQL • mySQL has several underlying database engines • InnoDB • Transactions & referential integrity • Not best performance, inefficient disk space usage • myIsam • Good performance but not foreign keys • myIsam compressed • Efficient I/O, good use of disk space but read-only • Can’t build indexes without uncompressing • Support for VLDB’s • Merged tables are similar to Oracle partitioning but implemented by the user • Harder to simulate hash partitioning, range partitioning by default • Problems of using the indexes of the merged tables • Query optimiser of mySQL • Compared with Oracle seems primitive

  14. MSD mySQL experience • We used myIsam compressed tables without any indexes • The configuration that required the less disk space • Faster to download • Once the data are local users can uncompress the data and build the recommended or any other indexes locally • We used merged tables • To also avoid data files larger than 8GB • And for performance reasons • Character-sets - collation • Textual data in mySQL are by default case insensitive • Only some character collations allow a similar behaviour with Oracle • Other details • Table names are by default case sensitive (problem with windows- unix file systems) • Choosing the appropriate numeric type (Integer versus Numeric)

  15. MSD Search Database Database Replication Why Replicate Replication Overview Components of the Replication Incremental Data Export – Import Incremental Replication Mechanism Summary

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