Execution Plan Cost

Luis Vargas <Luis.Vargas@cl.cam.ac.uk> writes:

At the backend, I'm measuring the cost of executing (via SPI_execute_plan)
the read-only plan of a simple query with no reference to tables. E.g.
simpleplan(int) AS SELECT $1 > 5

Executing this plan via SPI_execute takes around 70% more time than
directly executing the relevant operator function (int4gt) and using
DatumGetBool.

Only that much? I'd have expected it to be several hundred times
slower, considering that int4gt is an utterly trivial function and
executor startup/shutdown is a fairly heavyweight operation.

regards, tom lane

The read-only plan of the query (SELECT $1 > 5) is prepared, so there is
not parsing or planning. Any insight into what operations account for the
executor startup/shutdown time?

Thanks a lot,

Luis Vargas

On May 8 2008, Tom Lane wrote:

Luis Vargas <Luis.Vargas@cl.cam.ac.uk> writes:

At the backend, I'm measuring the cost of executing (via
SPI_execute_plan) the read-only plan of a simple query with no reference
to tables. E.g. simpleplan(int) AS SELECT $1 > 5

Executing this plan via SPI_execute takes around 70% more time than
directly executing the relevant operator function (int4gt) and using
DatumGetBool.

Only that much? I'd have expected it to be several hundred times
slower, considering that int4gt is an utterly trivial function and
executor startup/shutdown is a fairly heavyweight operation.

regards, tom lane

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