How a query is processed in embedded Teiid

[sarin_ashish]

Hi everyone,

I'm using Teiid in embedded mode. I was trying to debug the Teiid source code to see how Teiid processes an SQL query and fetches data. I saw that OioOjbectChannelFactory's write method is used to write request details (that includes the method name, class that contains the method, method arguments, and the SQL query to execute) to the socket. Now, I'm unable to find how the message written to the socket is used to execute the given SQL query and fetch data. It'd be great if someone can give me pointers on which class(es) I should add debug points to see how the SQL queries are processed by Teiid runtime.

regards

ashish

[rareddy]

I guess it is little more complex that that -:)

You need to start at RequestWorkItem and ConnectorWorkItem.

Ramesh..

[shawkins]

If you are looking at embedded, then you should skip looking at the socket layer entirely.  The main entry point for client/server interaction is DQPCore, and as Ramesh says the main coordinator for query processing is RequestWorkItem.  See both and other classes in the process package: teiid/engine/src/main/java/org/teiid/dqp/internal/process at master · teiid/teiid · GitHub

Once we develop a query plan (see the Request class) the RequestWorkItem controls the threading behavior and spawns ConnectorWorkItems to handle the source work - see teiid/engine/src/main/java/org/teiid/dqp/internal/datamgr at master · teiid/teiid · GitHub

[sarin_ashish]

Thanks Ramesh and Steven.

I'm using Teiid 8.7. I've created a sample application that deploys a VDB ZIP file in which a CSV file acts as the data source. I fire a select * from xyz query to get the data from this VDB. The query is successfully processed and I get the data from the VDB. I tried to debug my sample application by putting breakpoints in RequestWorkItem and ConnectorWorkItem classes but Eclipse never goes to these classes. Also, I do see that during debugging SocketServerInstanceImpl's send method is called to write a message to an object output stream. So, it looks like that the socket layer is coming into picture when I'm executing the SQL query.

regards

ashish

[shawkins]

It does not appear that you are using Teiid embedded - unless you specifically configured a socket transport to be used.

Otherwise you likely setup an AS instance to deploy the Teiid server into and are hitting that from your client.  Unless you have remote debugging enabled on the AS VM, your debugger will not see what is happening on the server side.

[sarin_ashish]

Thanks Steven. I realized my mistake. The connection string I was using was wrong. It was connecting to the standalone Teiid server.