USER MANUALS

How Web Services Query the Virtual DataPort Server

When a Web service receives a request, it executes a SQL statement (SELECT, INSERT, UPDATE, etc.). To do this, it behaves as any other Virtual DataPort client: it connects to Virtual DataPort with certain credentials and executes a query equivalent to the request received. This query may fail if the user associated to these credentials is not granted the appropriate privileges.

SOAP Web services: when you deploy a view as a SOAP Web service, by default the service has four operations:

  • getXXX: when invoked, the service executes a SELECT statement.

  • insertXXX: when invoked, the service executes an INSERT statement.

  • updateXXX: when invoked, the service executes an UPDATE statement.

  • deleteXXX: when invoked, the service executes a DELETE statement.

You can delete any of these operations if you do not want any client to perform them.

REST Web services: as opposed to SOAP Web services, REST Web services publish views and not operations over view. Therefore, when you publish a view, you are allowing external clients to perform the following operations on them:

  • SELECT_NAVIGATIONAL statements: when the service receives GET requests.

  • INSERT statements: when the service receives POST requests

  • UPDATE statements: when the service receives PUT requests.

  • DELETE statements: when the service receives DELETE requests.

The credentials used by the Web service to connect to Virtual DataPort depend on the authentication method selected. They fall into two categories (see the last two columns of the table Authentication methods supported by SOAP and REST Web services):

  1. “Uses the credentials of the Web service”: during the deployment of the Web service, the administrator selects a user, whose credentials will be used by the Web service to execute all the queries. In order for these queries to succeed, the selected user needs to have the right privileges to perform these queries.

    The section Web Service Container Status Table will explain how the administrator selects a user for the service.

  2. “Uses the Credentials of the Web Service’s Clients”: in order for these queries to succeed, the users that invoke the Web service need to have the right privileges to perform the queries that the service will execute on their behalf.

    For example, if the user bruce invokes an operation of the service, the service connects to Virtual DataPort with the credentials provided by bruce in his request. The query may or may not be executed depending on the privileges assigned to bruce. If later, the user scott invokes the same operation of the service, the service will connect to Virtual DataPort with the credentials provided by scott.

A Web service is a JEE web application, which contains a web.xml file. When you deploy a Web service or generate its WAR, and the service uses one of the authentication methods of the column “Uses the credentials of the Web service”, the user name and the encrypted password of the user selected during the deployment of the Web service are stored in the web.xml file. At runtime, the service uses these credentials to connect to Virtual DataPort and execute queries.

For the services that use one of these types of authentication, if you change the password of the user selected to deploy the Web service, you have to redeploy the Web service. Otherwise, all the invocations to this service will fail because the password send by the service will not be correct.

Connection from the Web Services to the Server

At runtime, the REST and SOAP Web services establish one or more connections with the Virtual DataPort server to query views and send the result to clients.

You can configure the parameters of these connections. The most important one is the use of a connection pool. If enabled, the connections opened by the Web service to Virtual DataPort are reused. In production environments, the use of the connections pool is strongly recommended.

The configuration parameters of the connection are:

  • Chunk Size (rows), Chunk timeout (milliseconds) and Query timeout (milliseconds). Their meaning is the same as in any other VDP client (see section Access through JDBC of the Developer Guide).

  • Enable Pool. Select this check box to enable the connection pool. We recommend enabling this option.

  • Initial number of connections. Initial number of connections opened by the pool.

  • Maximum number of active connections. Maximum number of connections in the pool. A negative value means there is no limit.

If you expect any of your Web services to receive a high number of concurrent requests, consider increasing the maximum number of threads that Tomcat will create to attend requests. To do this, read the section Increasing the Maximum Simultaneous Requests of the Denodo Platform Installation Guide.

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