Re: Cursors removed with commit - Mailing list pgsql-jdbc

Cursors generally only exist inside a transaction so the first problem makes sense.

==> yes, I agree

Apparently we aren't dealing with holdable cursors properly optimally though

==> holdable cursors cancels fetch ; OutOfMemory for our application

Best Regards,

----- Mail original -----
De: "Dave Cramer" <pg@fastcrypt.com>
À: "Christophe Canovas" <cc.ais40@wanadoo.fr>
Cc: "List" <pgsql-jdbc@postgresql.org>
Envoyé: Jeudi 21 Août 2014 15:12:47
Objet: Re: [JDBC] Cursors removed with commit

Cursors generally only exist inside a transaction so the first problem makes sense.


Apparently we aren't dealing with holdable cursors properly optimally though


Dave Cramer

dave.cramer(at)credativ(dot)ca
http://www.credativ.ca



On 20 August 2014 10:22, Christophe Canovas < cc.ais40@wanadoo.fr > wrote:


To be more explicit, here is my example :
private void displayMem() {
Runtime rt = Runtime.getRuntime();
long alloue = rt.totalMemory();
long libre = rt.freeMemory();
System.out.println("Free mem = " + libre + " / allocated = " + alloue);
}

public void testJdbcSRS() throws Exception {
String driver = "org.postgresql.Driver";
Class.forName(driver);

String acces = "jdbc:postgresql://<myserver>/<mydb>";
Connection con = java.sql.DriverManager.getConnection(acces, "<account>", "<pass>");
con.setAutoCommit(false);

Statement st = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);//,ResultSet.HOLD_CURSORS_OVER_COMMIT);
st.setFetchSize(10);
displayMem();
ResultSet rs = st.executeQuery("SELECT * FROM doc_index");
for (int i = 0 ; i < 100; i++) {
rs.next();
}
displayMem();
// Statement st2 = con.createStatement();
// st2.execute("DELETE FROM doc_index WHERE id=100");
// st2.execute("INSERT INTO doc_index(id,version) VALUES (100,1)");
// con.commit();
for (int i = 0 ; i < 100; i++) {
rs.next();
}
displayMem();

rs.close();
st.close();
con.close();
}


First run : OK

Remove the comments on lines on Statement st2 = ... to con.commit()
==> cursor error
(in that case the same table is updated, but i've tried on another table, and it's the same behavior)

Try to HOLD_CURSORS_OVER_COMMIT : it works, BUT the fetch is not used anymore ; the whole table is loaded in the memory (and in my case : OutOfMemory)


Regards,
Christophe

----- Mail original -----
De: "Christophe Canovas" < cc.ais40@wanadoo.fr >
À: pgsql-jdbc@postgresql.org
Envoyé: Mercredi 20 Août 2014 15:39:12
Objet: [JDBC] Cursors removed with commit



Hello,

I have a problem with my huge database ; using cursors (so using a transaction with noautocommit, statement with type_forward_only) make cursors removed if I update and save (commit) database values in the same transaction during the fetch loop.

Error message is : portal "C_03" doesn't exist

All is fine if the commit is done in a different transaction.

In more details, in the statement creation :
con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY, ResultSet.HOLD_CURSORS_OVER_COMMIT);
the last parameter seems to have no effect ... ?


Best Regards,
Christophe


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