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Thread: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Konstantin Izmailov
Date:
Is there a way to prevent transaction abort when preparing command in version 7.4?
 
I googled but haven't been able to find the answer. The issue occurs when our software trys to prepare a command that is already prepared (by the same or different app). PQprepare returns error and aborts current transaction. The company is not willing to upgrade from 7.4 to a later version due to risk.
 
SAVEPOINTs are not available in v.7.4. I'm looking at PQdescribePrepared function. What is the right solution?
 
Thank you
Konstantin

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Scott Marlowe
Date:
On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
> Is there a way to prevent transaction abort when preparing command in
> version 7.4?
>
> I googled but haven't been able to find the answer. The issue occurs when
> our software trys to prepare a command that is already prepared (by the same
> or different app). PQprepare returns error and aborts current transaction.
> The company is not willing to upgrade from 7.4 to a later version due to
> risk.
>
> SAVEPOINTs are not available in v.7.4. I'm looking at PQdescribePrepared
> function. What is the right solution?

Upgrading to a later version of pgsql, or don't issue that command
twice in a transaction.

The risk of upgrading is less than the risk of staying on an
unsupported version of pgsql.  The company that won't upgrade is
making a poorly informed decision.

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Konstantin Izmailov
Date:
Scott, thank you for the quick answer!
 
I think it would work if our software tracks which statements have already been prepared on the connection.

 
On Wed, Jun 23, 2010 at 8:25 PM, Scott Marlowe <scott.marlowe@gmail.com> wrote:
On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
> Is there a way to prevent transaction abort when preparing command in
> version 7.4?
>
> I googled but haven't been able to find the answer. The issue occurs when
> our software trys to prepare a command that is already prepared (by the same
> or different app). PQprepare returns error and aborts current transaction.
> The company is not willing to upgrade from 7.4 to a later version due to
> risk.
>
> SAVEPOINTs are not available in v.7.4. I'm looking at PQdescribePrepared
> function. What is the right solution?

Upgrading to a later version of pgsql, or don't issue that command
twice in a transaction.

The risk of upgrading is less than the risk of staying on an
unsupported version of pgsql.  The company that won't upgrade is
making a poorly informed decision.

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Scott Marlowe
Date:
On Thu, Jun 24, 2010 at 12:28 AM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
> Scott, thank you for the quick answer!
>
> I think it would work if our software tracks which statements have already
> been prepared on the connection.

Good chance of it, but honestly, running such an old and now
unsupported version of pgsql is just asking for trouble.  I bet
they're not even on the latest 7.4 version, or close, right?

Getting them onto a newer, supported version should become a priority,
because if you guys show up on the lists with some horrible data loss
problem or bug, and your version is 7.4, you're gonna have a hard time
finding someone who can remember enough about that version to help.

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Tom Lane
Date:
Scott Marlowe <scott.marlowe@gmail.com> writes:
> On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
>> The company�is not willing to upgrade from 7.4 to a later version due to
>> risk.

> The risk of upgrading is less than the risk of staying on an
> unsupported version of pgsql.  The company that won't upgrade is
> making a poorly informed decision.

Indeed.  Point out to them that 7.4 is going to be unsupported after the
end of this month:
http://wiki.postgresql.org/wiki/PostgreSQL_Release_Support_Policy

If they don't have a plan to get off of 7.4 within the pretty near
future, they're fools.

            regards, tom lane

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Konstantin Izmailov
Date:
lol
 
Seriosly, this customer issues resulted in improvement of the way our driver prepares statements. Keeping the map of prepared statements names is actually faster than using Savepoints (less roundtrips to server).

I found that DECLARE ... CURSOR FOR ... cannot be prepared. Basically I'm looking for a way to prepare a complex query and then use cursor for reading tuples. Is this possible?
This works: PREPARE abcd AS SELECT * FROM test; EXECUTE abcd;
This does not work: PREPARE sdsdsd AS DECLARE csr1 CURSOR FOR SELECT * FROM test;
This does not work (after prepared the query): DECLARE csr1 CURSOR FOR EXECUTE abcd;
 
Thank you!
Konstantin
On Wed, Jun 23, 2010 at 9:41 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Scott Marlowe <scott.marlowe@gmail.com> writes:
> On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
>> The company is not willing to upgrade from 7.4 to a later version due to
>> risk.

> The risk of upgrading is less than the risk of staying on an
> unsupported version of pgsql.  The company that won't upgrade is
> making a poorly informed decision.

Indeed.  Point out to them that 7.4 is going to be unsupported after the
end of this month:
http://wiki.postgresql.org/wiki/PostgreSQL_Release_Support_Policy

If they don't have a plan to get off of 7.4 within the pretty near
future, they're fools.

                       regards, tom lane

Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Konstantin Izmailov
Date:
Looks like other people were asking similar question, but there is no answer: http://forums.devshed.com/postgresql-help-21/combine-prepare-and-declare-cursor-437562.html

On Mon, Jun 28, 2010 at 1:00 AM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
lol
 
Seriosly, this customer issues resulted in improvement of the way our driver prepares statements. Keeping the map of prepared statements names is actually faster than using Savepoints (less roundtrips to server).

I found that DECLARE ... CURSOR FOR ... cannot be prepared. Basically I'm looking for a way to prepare a complex query and then use cursor for reading tuples. Is this possible?
This works: PREPARE abcd AS SELECT * FROM test; EXECUTE abcd;
This does not work: PREPARE sdsdsd AS DECLARE csr1 CURSOR FOR SELECT * FROM test;
This does not work (after prepared the query): DECLARE csr1 CURSOR FOR EXECUTE abcd;
 
Thank you!
Konstantin
On Wed, Jun 23, 2010 at 9:41 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Scott Marlowe <scott.marlowe@gmail.com> writes:
> On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
>> The company is not willing to upgrade from 7.4 to a later version due to
>> risk.

> The risk of upgrading is less than the risk of staying on an
> unsupported version of pgsql.  The company that won't upgrade is
> making a poorly informed decision.

Indeed.  Point out to them that 7.4 is going to be unsupported after the
end of this month:
http://wiki.postgresql.org/wiki/PostgreSQL_Release_Support_Policy

If they don't have a plan to get off of 7.4 within the pretty near
future, they're fools.

                       regards, tom lane


Re: PQprepare in PostgreSQL 7.4 (lack of SAVEPOINTs)

From
Konstantin Izmailov
Date:
I have figured it out and everything works wonderfully!!!
 
Here is test code that allows preparing a query with cursor using libpq library:
 
PGconn* conn = PQconnectdb("host=localhost dbname=postgres user=postgres password=12345 port=5432");
 
PGresult* res = ::PQexec(conn, "START TRANSACTION", 0, 0);     // need transaction scope for the cursor
 
res = ::PQprepare(conn, "abcd", "DECLARE cur1 CURSOR FOR SELECT * FROM test", 0, NULL);
 
res = ::PQexecPrepared(conn, "abcd", 0, 0, 0, 0, 0, 0);

res = ::PQexec(conn, "FETCH FORWARD 100 FROM cur1", 0, 0);

int cColumns = PQnfields(res);

int cRows = PQntuples(res);

for (int field_num = 0; field_num < cColumns; field_num++)

{

char* szName = PQfname(res, field_num);

int nColumnSize = PQfsize(res, field_num);

Oid nType = PQftype(res, field_num);

int nMod = PQfmod(res, field_num);

}

res = ::PQexec(conn, "ABORT", 0, 0);

On Mon, Jun 28, 2010 at 9:11 AM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
Looks like other people were asking similar question, but there is no answer: http://forums.devshed.com/postgresql-help-21/combine-prepare-and-declare-cursor-437562.html

On Mon, Jun 28, 2010 at 1:00 AM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
lol
 
Seriosly, this customer issues resulted in improvement of the way our driver prepares statements. Keeping the map of prepared statements names is actually faster than using Savepoints (less roundtrips to server).

I found that DECLARE ... CURSOR FOR ... cannot be prepared. Basically I'm looking for a way to prepare a complex query and then use cursor for reading tuples. Is this possible?
This works: PREPARE abcd AS SELECT * FROM test; EXECUTE abcd;
This does not work: PREPARE sdsdsd AS DECLARE csr1 CURSOR FOR SELECT * FROM test;
This does not work (after prepared the query): DECLARE csr1 CURSOR FOR EXECUTE abcd;
 
Thank you!
Konstantin
On Wed, Jun 23, 2010 at 9:41 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Scott Marlowe <scott.marlowe@gmail.com> writes:
> On Wed, Jun 23, 2010 at 10:55 PM, Konstantin Izmailov <pgfizm@gmail.com> wrote:
>> The company is not willing to upgrade from 7.4 to a later version due to
>> risk.

> The risk of upgrading is less than the risk of staying on an
> unsupported version of pgsql.  The company that won't upgrade is
> making a poorly informed decision.

Indeed.  Point out to them that 7.4 is going to be unsupported after the
end of this month:
http://wiki.postgresql.org/wiki/PostgreSQL_Release_Support_Policy

If they don't have a plan to get off of 7.4 within the pretty near
future, they're fools.

                       regards, tom lane