I want to make an example of using parameterized path

Hello:

I have some questions about parameterized path.

I have heard that it is a new feature in PG9.2.

I digged for information of parameterized path, but found few(maybe my
method is not right).

My FIRST question is:

What is "parameterized path " for?

Is the following a correct example of activating "parameterized path" being
created?

I found an example by googling. I tried it:

--making data:

postgres=# create table tst01(id integer);

CREATE TABLE

postgres=#

postgres=# insert into tst01 values(generate_series(1,100000));

INSERT 0 100000

postgres=#

postgres=# create index idx_tst01_id on tst01(id);

CREATE INDEX

postgres=#

--runing:

postgres=# prepare s(int) as select * from tst01 t where id < $1;

PREPARE

postgres=# explain execute s(2);

QUERY PLAN

---------------------------------------------------------------------------------

Index Only Scan using idx_tst01_id on tst01 t (cost=0.00..8.38 rows=1 width=4)

Index Cond: (id < 2)

(2 rows)

postgres=# explain execute s(100000);

QUERY PLAN

---------------------------------------------------------------

Seq Scan on tst01 t (cost=0.00..1693.00 rows=100000 width=4)

Filter: (id < 100000)

(2 rows)

postgres=#

When I just send sql of " select * from tst01 t where id <2" , it will
also produce index only scan plan.

When I just send sql of " select * from tst01 t where id < 100000", it
will also produce seq scan plan.

So I think that the above example can not show that "parameterized path"
has been created.

Maybe:

"parameterized path" is special method to do something for a parse tree's
plan in ahead I think,

In order to improve prepared statement's planning and executing speed
more.

Is this understanding right?

My SECOND question is:

For the above example I used,

I found that as if "parameterized path" is not created.

For my above example,

I can find calling relationship of the following:

PostgresMainàexec_simple_queryàpg_plan_queriesàpg_plan_queryàplannerà
standard_plannerà

àsubquery_planneràgrouping_planneràquery_planneràmake_one_relà
set_base_rel_pathlistsà

àset_rel_pathlistàset_plain_rel_pathlist

The set_plain_rel_pathlist calls create_seqscan_path via add_path
function's parameter.

Then In create_seqscan_path function , get_baserel_parampathlist function
returned null.

As following:

pathnode->param_info = get_baserel_parampathinfo(root, rel,required_outer);

So I got no param_info . Does that mean : parameteried path is not
created ?

If so, Is there any option to let the parameterized path being created? And
how to observe it?

Thanks!