Postgres prepare statement caching issue in postgres command line

Soumya Prasad Ukil <soumyo_ju@yahoo.co.in> writes:

I have been using postgres prepare statement feature through JDBC. I could see the same prepare statement multiple times, parsing is not happening in postgres backend, which is expected. However I do the same in psql command line, that does not happen. It goes to parsing every time I execute

Perhaps "set plan_cache_mode = force_generic_plan" would help you.

Bear in mind that this is likely to be a net loss overall.

regards, tom lane

On 5/22/21 4:11 PM, Tom Lane wrote:

Soumya Prasad Ukil <soumyo_ju@yahoo.co.in> writes:

I have been using postgres prepare statement feature through JDBC. I could see the same prepare statement multiple times, parsing is not happening in postgres backend, which is expected. However I do the same in psql command line, that does not happen. It goes to parsing every time I execute

Perhaps "set plan_cache_mode = force_generic_plan" would help you.

Bear in mind that this is likely to be a net loss overall.

This (poorly) works around the problem, but does not answer the question.

--
Angular momentum makes the world go 'round.

On 5/22/21 1:25 PM, Soumya Prasad Ukil wrote:

I have been using postgres prepare statement feature through JDBC. I
could see the same prepare statement multiple times, parsing is not
happening in postgres backend, which is expected. However I do the same
in psql command line, that does not happen. It goes to parsing every
time I execute

Using the following query:

postgres=> PREPARE parallel_execute1(text, text) AS insert into actor
(first_name, last_name) values ($1, $2);
postgres=> PREPARE parallel_execute2(int, int) AS insert into film_actor
(actor_id, film_id) values($1, $2);
postgres=> execute parallel_execute1;
postgres=> execute parallel_execute2;

Where are the arguments for the parameters?

I have executed both prepared statements 10 times. I could see every
time both queries went through parsing. How do I make sure that they do
not need parsing in command line? JDBC it works in expected manner. Same
code does not go for parsing each time. How can I have same behaviour in
pgsql command line?

How are you determining the above?

--
Adrian Klaver
adrian.klaver@aklaver.com

postgres=> execute parallel_execute1('a', 'b');postgres=> execute parallel_execute2(1, 2);
I have enabled pg_stats_statement chrome extension. I have enabled postgres log inside post_parse_analyze_hook  and also debugging through gdb using break point. I see it is always going through parse callback. But when I use the same sql statement using Java program through JDBC prepare statement, it does not go to parse callback all the time. It stops after 6th iteration onwards. What I have read in JDBC is that, postgres has a default threshold for prepare statement to 5 https://jdbc.postgresql.org/documentation/head/server-prepare.html. But after 6th statement onwards, what I see parse callback is not triggered. However the same does not happen in psql command line. If I execute the same statement 10 times, all the times it goes through parsing. Not sure what JDBC does extra. 

On Sunday, 23 May, 2021, 03:53:55 am IST, Adrian Klaver <adrian.klaver@aklaver.com> wrote:

On 5/22/21 1:25 PM, Soumya Prasad Ukil wrote:

I have been using postgres prepare statement feature through JDBC. I
could see the same prepare statement multiple times, parsing is not
happening in postgres backend, which is expected. However I do the same
in psql command line, that does not happen. It goes to parsing every
time I execute

Using the following query:

postgres=> PREPARE parallel_execute1(text, text) AS insert into actor
(first_name, last_name) values ($1, $2);
postgres=> PREPARE parallel_execute2(int, int) AS insert into film_actor
(actor_id, film_id) values($1, $2);
postgres=> execute parallel_execute1;
postgres=> execute parallel_execute2;

Where are the arguments for the parameters?

I have executed both prepared statements 10 times. I could see every
time both queries went through parsing. How do I make sure that they do
not need parsing in command line? JDBC it works in expected manner. Same
code does not go for parsing each time. How can I have same behaviour in
pgsql command line?

How are you determining the above?

--
Adrian Klaver
adrian.klaver@aklaver.com

On 5/23/21 12:04 AM, Soumya Prasad Ukil wrote:

postgres=> execute parallel_execute1('a', 'b');
postgres=> execute parallel_execute2(1, 2);

I have enabled pg_stats_statement chrome extension. I have enabled
postgres log inside post_parse_analyze_hook

and also debugging through gdb using break point. I see it is always
going through parse callback. But when I use the same sql statement
using Java program through JDBC prepare statement, it does not go to
parse callback all the time. It stops after 6th iteration onwards. What
I have read in JDBC is that, postgres has a default threshold for
prepare statement to 5
https://jdbc.postgresql.org/documentation/head/server-prepare.html
<https://jdbc.postgresql.org/documentation/head/server-prepare.html&gt;.
But after 6th statement onwards, what I see parse callback is not
triggered. However the same does not happen in psql command line. If I
execute the same statement 10 times, all the times it goes through
parsing. Not sure what JDBC does extra.

Take a look at the Notes section here:

https://www.postgresql.org/docs/current/sql-prepare.html

It goes into detail on how a PREPARE statement is handled as regards
parsing. See if the conditions mentioned there cover your psql case or not.

On Sunday, 23 May, 2021, 03:53:55 am IST, Adrian Klaver
<adrian.klaver@aklaver.com> wrote:

On 5/22/21 1:25 PM, Soumya Prasad Ukil wrote:

I have been using postgres prepare statement feature through JDBC. I
could see the same prepare statement multiple times, parsing is not
happening in postgres backend, which is expected. However I do the same
in psql command line, that does not happen. It goes to parsing every
time I execute

Using the following query:

postgres=> PREPARE parallel_execute1(text, text) AS insert into actor
(first_name, last_name) values ($1, $2);
postgres=> PREPARE parallel_execute2(int, int) AS insert into film_actor
(actor_id, film_id) values($1, $2);
postgres=> execute parallel_execute1;
postgres=> execute parallel_execute2;

Where are the arguments for the parameters?

I have executed both prepared statements 10 times. I could see every
time both queries went through parsing. How do I make sure that they do
not need parsing in command line? JDBC it works in expected manner. Same
code does not go for parsing each time. How can I have same behaviour in
pgsql command line?

How are you determining the above?

--
Adrian Klaver
adrian.klaver@aklaver.com <mailto:adrian.klaver@aklaver.com>

--
Adrian Klaver
adrian.klaver@aklaver.com