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Appendix D. Known problems and limitations

D.1. Known problems and limitations
D.1.1. Known problems
D.1.2. Limitations

D.1. Known problems and limitations

D.1.1. Known problems

  • Platforms
    • OGSA-DAI 3.0 does not compile under Java 1.6. This is due to changes in java.sql APIs (in which both additional methods and classes have been added) from earlier versions of Java. The OGSA-DAI team may release a Java 1.6 patch in the near future.
    • The setenv scripts don't set CLASSPATHs correctly under Cygwin.
  • Interacting with databases
    • The standard Oracle JDBC driver does not conform to the JDBC API for insertion of BLOBs and so OGSA-DAI does not currently support the addition of BLOBs to tables in Oracle databases.
    • The table-name tag in WebRowSet XML is empty in results produced by Oracle or SQLServer. This is a problem of the JDBC drivers that do not provide table names in the metadata of a java.sql.ResultSet.
    • Meta-data from a database, returned by ExtractTableSchema, can be case-sensitive depending on the database used. For example, MySQL might return a table called littleblackbook while DB2 returns LITTLEBLACKBOOK.
    • If an error occurs during execution of a relational activity then server-side information may be returned to the client. This is because OGSA-DAI does not, as yet, parse java.sql.SQLExceptions from database drivers to identify problems caused by a client (e.g. a syntactically-incorrect SQL query) and those due to server-side failures (e.g. loss of connection to a database).
    • Though this is not OGSA-DAI specific, a user encountered a problem using the standard MySQL driver class org.gjt.mm.mysql.Driver from the mysql-connector-java-5.0.5 driver JAR in conjunction with MySQL version mysql-4.1.20-1.RHEL4.1 running on Red Hat. Even though they had provided the database name as part of the database connection URL, e.g. 
      jdbc:mysql://localhost:3306/dbname
      They had to specify the database name in their queries also, e.g. 
      SELECT * FROM dbname.table
  • Performance and scalability
    • Forwarding or retrieving very large amounts of data to/from an OGSA-DAI service may give rise to java.lang.OutOfMemoryError errors on the OGSA-DAI server. See Chapter 22, Best practice.
    • Attempting to get large amounts of data via a synchronous request can cause a server-side java.lang.OutOfMemoryError. This can be avoided by creating a data source and streaming the query data into this (via the WriteToDataSource activity) then pulling the data back to a client via a data source service. See Chapter 22, Best practice.
    • If using OGSA-DAI on a cluster with a single storage node then problems will arise when creating many resources (e.g. data sources or data sinks) simultaneously if the storage node does not support atomic file locking. The OGSA-DAI persistence components will attempt to access the resource template file for the resource being created many times simultaneously and will run into problems. This could be addressed by either ensuring that the storage node supports atomic file locking or developing a new OGSA-DAI persistence manager (either by modifying the existing one to support more effective concurrent file access or providing a new one that supports configuration from a database).
  • Miscellaneous
    • The uk.org.ogsadai.common.msgs.DAILogger methods can sometimes log the wrong line numbers. Searching the logs will usually reveal where the problem actually arose.
    • If a client does not provide a certificate then using deliverFromGridFTP and deliverToGridFTP in a request the transfer will fail.

D.1.2. Limitations

  • Platforms
    • Security
      • Our implementations of inter-service delivery activities (ObtainFromDataSource and DeliverToDataSink) do not at present support secure inter-service communications. This does not however preclude us providing these at a future date.
      • Encrypted login files are unsupported.
    • Activities
      • The sub-workflow API by which an activity can spawn a sub-workflow (as used in the SQLBag activity for example) is a proof-of-concept only. We intend to refactor the API for invoking sub-workflows at a future date to make it more usable.
      • In the source code there are references to the notion of activity contracts. These are intended to help support the use of activities in different roles e.g. the SQLBag could be exposed as an SQLBag or as an SQLQuery activity. We will elaborate on this concept at a later date (when we have had a chance to experiment).
      • Some of our activities, e.g. 
        uk.org.ogsadai.activity.sql.SQLBagActivity
uk.org.ogsadai.activity.sql.SQLResilientActivity
uk.org.ogsadai.activity.pipeline.AutomaticTee
        use hard-coded activity names to identify the activity or activities in sub-workflows they splice into workflows. This means that you should take care when renaming activities exposed by resources, especially block activities. This problem will be most likely manifested as an unsupported activity error.
      • Creation or deletion of databases within DB2 is not currently supported.
      • Creation or deletion of databases within Oracle is not currently supported.
      • SQL Server IMAGE column type is not currently supported.
      • deliverFromGridFTP and deliverToGridFTP do not allow the setting of certain GridFTP parameters.
      • Client toolkit support for XPathQuery and XQuery activities does not currently parse data in a request status into an org.xmldb.api.base.ResourceSet object.
    • Deployment

      • When building an OGSA-DAI Axis WAR file the service WSDL is customised to include the host and port on which Tomcat is running (which you specify at the command-line when building the WAR).

        While OGSA-DAI WAR files can be dropped into Tomcats running on other hosts or ports and the services will be usable using OGSA-DAI clients, any attempt to use the service WSDL may run into problems as the WSDL will contain the host and port originally specified when the WAR was built. To work round this you can either:

        • Rebuild the WAR file using an OGSA-DAI Axis binary distribution.
        • Or unZIP the WAR file, edit the host and ports encoded in the WSDL in the six schema/ogsadai/axis-specific-wsdl/*/*_service_service.wsdl files and then reZIP the WAR.
        • The JSP pages are prototypes. We may revise and extend the functionality of these at a later date.
    • Miscellaneous
      • BLOBs and CLOBs are currently only held in-memory with consquent implications on memory usage.
      • OGSA-DAI data request execution resources and implementations of JDBC, XMLDB and file system data resources do not support use of the destroy operation. It is a no-op.

      • The default OGSA-DAI resource and activity managers 

        uk.org.ogsadai.activity.SimpleActivityManager
uk.org.ogsadai.resource.SimpleResourceManager

        cache activity specifications and resources in in-memory hash tables. They do not check for changes in any persisted configuration associated with the activity specifications or resources once the associated objects are in the cache.

      • The default OGSA-DAI file-based resource persistence and configuration manager uk.org.ogsadai.persistence.file.resource.SimpleFileResourceStateDAO only handles the persistence and restoration of resource properties or session state that are Strings.
      • The WSRF operation SetResourceProperty is not supported by OGSA-DAI services.
      • The OGSA-DAI GT wrapper class uk.org.ogsadai.service.gt.resource.GTResourceProperty methods 
        add(X)
clear()
get(int)
remove(Object)
set(int, Object)
        are currently not supported. These would need to convert from XML fragments into objects.
      • There is no cleanup if client-service communication times out. Service will just reply as usual.
      • The uk.org.ogsadai.common.BinaryLob class contains unimplemented methods which throw java.lang.UnsupportedOperationException.
      • Conversion of java.sql.ResultSet to XML WebRowSet returns empty key-column and map properties in the properties element.
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