Re: Prepared Statements

"A prepared statement has a name and a CachedPlanSource. They are stored
in a hash table. See StorePreparedStatement() function. If you grep for
callers of StorePreparedStatement(), you'll see that there are two: one
in processing an EXECUTE statement, and one in handling the Extended
Query Protocol."

Thank you, the functions in the grep are the ones I was looking for.

Patrick

On Sun, Oct 4, 2020 at 11:32 PM Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:

> On 02/10/2020 23:10, Patrick REED wrote:
> > Hi,
> >
> > I am having a hard time pinning down which function creates a prepared
> > statement. Say in some language I create a Prepared Statement and send
> > it off. Before the first time I execute the prepared statement, which
> > function is the one that 'creates' the prepared statement. In other
> > words, which function stores it. I know that StorePreparedStatement will
> > cache it, but is there anything else.
> >
> > e.g.
> > In your favorite language:
> >
> > |String statement = "Insert into table_one values 10"; PreparedStatement
> > insert = con.prepareStatement(statement); insert.execute() |
> >
> > The very first time, does it store this just in the plancache or does it
> > do something different to 'know' it has stored a Prepared Statement, so
> > next time it will invoke it.
>
> Most drivers use what the Extended Query Protocol. The client first
> sends a Parse message that contains the SQL text. Next, it sends a Bind
> message that contains the query parameters, and Execute to execute it.
> The Bind+Execute steps can be repeated multiple times, with different
> query parameters. The PREPARE and EXECUTE statements do essentially the
> same thing.
>
> In the server code, there is the plan cache. The plan cache tracks when
> a plan needs to be invalidated and the query replanned. The handle to an
> entry in the plan cache is a CachedPlanSource, which contains the SQL
> original and enough information to (re-)plan the query as needed. The
> plan cache has entries for all the prepared statements, but also for
> statements in PL/pgSQL functions, statements prepared with SPI_prepare()
> etc. The plan cache doesn't know or care where the statements came from,
> they are all treated the same.
>
> A prepared statement has a name and a CachedPlanSource. They are stored
> in a hash table. See StorePreparedStatement() function. If you grep for
> callers of StorePreparedStatement(), you'll see that there are two: one
> in processing an EXECUTE statement, and one in handling the Extended
> Query Protocol.
>
> - Heikki
>