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query metadata tables SOURCE_CHANGES()

Hi, I found these functions to query metadata: https://community.denodo.com/docs/html/browse/6.0/vdp/vql/stored_procedures/predefined_stored_procedures/predefined_stored_procedures we use `SOUCE_CHANGES()` in a select condition and wondering how this function works. - is it possible to check the workflow of this function? - is it possible to customize (first rename) these stored procedures in denodo, or create or own procedure on metadata? - is it possible to query metadata tables directly? or do we need to use the predefined procedures described in the link for metadata? I did not find any information about browsing original metadata tables without a stored procedure. kind regards
user
12-03-2018 06:20:00 -0400
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3 Answers

Hi, The SOURCE_CHANGES() Stored Procedure detects the differences between the schema of a base and its underlying data source. For example, if a new field is added in the underlying data source, then the Stored Procedure identifies that new field. Using Scheduler Administration Tool, you could automate the execution of SOURCE_CHANGES() and export the results. You could refer our Knowledge Base article [How to detect changes in data sources](https://community.denodo.com/kb/view/document/How%20to%20detect%20changes%20in%20data%20sources?category=Data+Sources) for more information. It is possible to create your own Stored Procedure in Virtual DataPort using [Denodo4E](https://community.denodo.com/docs/html/browse/6.0/platform/installation/denodo4e/denodo4e#denodo4e) extension available in the directory <DENODO_HOME>/tools/denodo4e and deploy the developed Custom Stored Procedure in Virtual DataPort. You could find samples for Virtual DataPort Custom Stored Procedure in the directory, <DENODO_HOME>\samples\vdp\storedProcedures. For more information on creating custom Stored Procedure, have a look at [Developing Stored Procedures](https://community.denodo.com/docs/html/browse/6.0/vdp/developer/developing_extensions/developing_stored_procedures/developing_stored_procedures) section of Virtual DataPort Developer Guide. In order to view some of the metadata information about the elements in Virtual DataPort Administration Tool, you could use the Tools > [Catalog search](https://community.denodo.com/docs/html/browse/6.0/vdp/administration/installation_and_execution/launching_the_virtual_dataport_administration_tool/catalog_search#catalog-search) option. If you would like to get a detailed metadata information, then you need to use the Predefined Stored Procedure. Hope this helps !!
Denodo Team
12-03-2018 07:29:21 -0400
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thank you for this information for a task, I have joined SOURCE_CHANGES() with CATALOG_ELEMENTS(). By executing the join of both procedures, it can take up to a few minutes to check for almost 50 tables. We think that SOURCE_CHANGES() will create a connection for each table found in CATALOG_ELEMENTS() using JDBC to compare source information. Is this possible? For this case, we thought to create a custom procedure to check for all tables in one database_name. Is it possible to check the code used in SOURCE_CHANGES() and recreate this in a custom procedure?
user
12-03-2018 07:45:20 -0400
Hi, The JOIN operation is working as expected. Also, you could check if a new connection is created while executing using the [Diagnostic and Monitoring Tool](https://community.denodo.com/docs/html/browse/6.0/vdp/dmt/monitoring/monitoring_servers/monitoring_servers#monitoring-servers). As the SOURCE_CHANGES() is a pre-defined Stored Procedure, you could create your own Custom Stored Procedure based on your requirement. Hope this helps !!
Denodo Team
27-03-2018 08:54:21 -0400
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