[Postgres-xc-general] Feature request - Fast Query Shipping for Select with array element access

[Javier H. <jhe...@ce...>]

Hello,

     I am not sure if this is the right mailing list for sending Feature 
request, if not, sorry for the inconvenience.

     I know you are working on improvements to the planner (Feature 
Request #95). One important for my project is the ability to use FQS for 
queries that reference elements in an array column. One example:

     CREATE TABLE TestArray (id SERIAL, flux FLOAT4*[]*, error FLOAT*[]*);

     SELECT flux, error FROM TestArray WHERE id = 12; -- Planner uses FQS
     SELECT flux[1], error[1] FROM TestArray WHERE id = 12; -- Planner 
uses Remote query and completes in coordinator

     I am beginning to dig in the code and I think I have a temporary 
solution:


src/backend/optimizer/util/pgxcship.c:709

         case T_ArrayRef:
             /*
              * When multiple values of of an array are updated at once
              * FQS planner cannot yet handle SQL representation correctly.
              * So disable FQS in this case and let standard planner 
manage it.
              */
             if (sc_context->sc_query != NULL && 
sc_context->sc_query->commandType == CMD_SELECT) {
                     pgxc_set_exprtype_shippability(exprType(node), 
sc_context);
             } else {
                     pgxc_set_shippability_reason(sc_context, 
SS_UNSUPPORTED_EXPR);
                     pgxc_set_exprtype_shippability(exprType(node), 
sc_context);
             }
             break;


     The original code is always marking the query as 
SS_UNSUPPORTED_EXPR, but according to the existing comment I think my 
change is safe for Select. Isn't it?


Thank you very much,

-- 
Javier Hernández
Ingeniero de Bases de Datos
Centro de Estudios de Fisica del Cosmos de Aragon (ceFca)
http://www.cefca.es
Plza San Juan Nº 1, Planta 2ª
E-44001 Teruel (Spain)
Phone: +34 978 221266 Ext.1105
Fax:   +34 978 611801