From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Vaibhav Kaushal <vaibhavkaushal123(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: When and how many times does ExecSetParamPlan executes? |
Date: | 2011-03-25 18:37:19 |
Message-ID: | 14810.1301078239@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Vaibhav Kaushal <vaibhavkaushal123(at)gmail(dot)com> writes:
> Hello all,
> I was going through the Expression Evaluator and was trying to
> understand how the expressions are formed and evaluated. I was informed
> on the IRC channel that the PARAM nodes are quite important and many
> well written client applications use PARAMs for sending query to the
> backend. I found while looking at the ExecEvalParam function that a call
> is made to the ExecSetParamPlan for the first time when the PARAM is
> caught in the ExprState tree.
> I am confused about how many times the call is made to the
> ExecSetParamPlan funtion.
Indeed ... ExecSetParamPlan has nothing at all to do with Params
representing values coming from a client (PARAM_EXTERN parameters).
It's used in connection with PARAM_EXEC parameters that represent
the outputs of InitPlan subplans (that is, execute-only-once subplans).
regards, tom lane
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