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Hello all,
I have a problem invocating SELECT statements using Java JDBC driver
having
a remote communication between PostgreSQL database client-server through
Internet.
If I run a database client (a java application using JDBC3 or JDBC4
driver)
and launch a simple SELECT statement against remote server (through
Internet), the 'executeQuery' method never ends. This problem only occurs
if
the amount of data retrieved by the SELECT statement exceeds a certain
value, the communication between client and server is through Internet and
the client app is executed on linux (tested on Kubuntu 7.04 and 7.10). The
problem does NOT occur if the communication is through loopback interface
or
local network. In addition if i execute the same client app on Windows
(tested on Windows XP), whatever the communication may be (local, local
network or internet) it works fine.
Since the problem doesn't appear on windows i think the problem may be
related to the interaction between the JDBC Driver and the linux Java
Virtual Machine. So I have monitored the communications using "Wireshark
Network Analizer". After analizing the exchanged PGSQL (contains SELECT
statement data) and TCP (ACK messages) messages between client and server
it
looks like the client closes the communication after a concrete number of
PGSQL and TCP messages with the database server, so the server detects
that
the client doesn't acknowledge to PGSQL messages and retries several more
times (~8 times) without response from the client.
--------------------
if someone wants reproduce the problem only has to follow this steps.
Create
a PostgreSQL database with the following table
CREATE TABLE TABLE1 (
field1 integer NOT NULL,
CONSTRAINT pk_table1 PRIMARY KEY (field1)
)
I have used the PostgreSQL database server (v8.2) executed in Kubuntu
7.10at the server side.
Then create a Java application which send a simple SELECT statement. For
example
try {
Class.forName("org.postgresql.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
try {
conn = DriverManager.getConnection
("jdbc:postgresql://AAA.BBB.CCC.DDD:5432/","user","password");
} catch (SQLException e) {
e.printStackTrace();
}
Statement st = null;
try {
st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT * FROM TABLE1");
rs.close();
st.close();
} catch (SQLException e) {
e.printStackTrace();
}
I have executed the client on Kubuntu 7.04 and 7.10 using all JDBC3 (JVM
1.5)
and JDBC4 (JVM 1.6) drivers for testing.
Once you have installed the database server in any REMOTE PC, fill TABLE1
with 1012 rows (or more) and execute the Java client. The client should be
waiting indefinitely when running executeQuery("SELECT * FROM TABLE1"); On
the other hand, if the table contains 1011 rows or less the Java app works
fine (at least for me).
--------------------
Tip:
After testing successfully the client on windows i don't think that's a
firewall problem on the server side. Besides when making tests on linux
i've
even tried to disable the firewall (at the client), so i also don't think
this is failing. Anyway the connection is established, and some packets
are
exchanged.
Also remember that it works fine even from a linux client when having both
client and server on the same network (a lan, for example).
Thanks in advance
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Hello all,<br><br>I have a problem invocating SELECT statements using Java
JDBC driver having a remote communication between PostgreSQL database
client-server through Internet.<br>If I run a database client (a java
application using JDBC3 or JDBC4 driver) and launch a simple SELECT
statement against remote server (through Internet), the
'executeQuery' method never ends. This problem only occurs if the
amount of data retrieved by the SELECT statement exceeds a certain value,
the communication between client and server is through Internet and the
client app is executed on linux (tested on Kubuntu 7.04 and 7.10). The
problem does NOT occur if the communication is through loopback interface
or local network. In addition if i execute the same client app on Windows
(tested on Windows XP), whatever the communication may be (local, local
network or internet) it works fine. <br>
<br>Since the problem doesn't appear on windows i think the problem
may be related to the interaction between the JDBC Driver and the linux
Java Virtual Machine. So I have monitored the communications using
"Wireshark Network Analizer". After analizing the exchanged
PGSQL (contains SELECT statement data) and TCP (ACK messages) messages
between client and server it looks like the client closes the
communication after a concrete number of PGSQL and TCP messages with the
database server, so the server detects that the client doesn't
acknowledge to PGSQL messages and retries several more times (~8 times)
without response from the client.<br>
<br>--------------------<br><br>if someone wants reproduce the problem
only has to follow this steps. Create a PostgreSQL database with the
following table<br><br>CREATE TABLE TABLE1 (<br> field1 integer NOT
NULL,<br> CONSTRAINT pk_table1 PRIMARY KEY (field1)<br>
)<br><br>I have used the PostgreSQL database server (v8.2) executed in
Kubuntu 7.10 at the server side.<br><br>Then create a Java application
which send a simple SELECT statement. For example<br><br>try
{<br>
Class.forName("org.postgresql.Driver");<br>
} catch (ClassNotFoundException e) {<br>
e.printStackTrace();<br>}<br><br>try {<br> conn =
DriverManager.getConnection("jdbc:postgresql://AAA.BBB.CCC.DDD:5432/","user","password");<br>}
catch (SQLException e) {<br>
e.printStackTrace();<br>}
<br><br>Statement st = null;<br>try {<br> st =
conn.createStatement();<br><br> ResultSet rs =
st.executeQuery("SELECT * FROM TABLE1");<br><br>
rs.close();<br> st.close();<br>
} catch (SQLException e) {<br>
e.printStackTrace();<br>}<br><br>I have executed the client on
Kubuntu 7.04 and 7.10 using all JDBC3 (JVM 1.5) and JDBC4 (JVM 1.6)
drivers for testing.<br><br>Once you have installed the database server in
any REMOTE PC, fill TABLE1 with 1012 rows (or more) and execute the Java
client. The client should be waiting indefinitely when running
executeQuery("SELECT * FROM TABLE1"); On the other hand, if the
table contains 1011 rows or less the Java app works fine (at least for
me).<br>
<br>--------------------<br><br>Tip:<br><br>After testing successfully the
client on windows i don't think that's a firewall problem on the
server side. Besides when making tests on linux i've even tried to
disable the firewall (at the client), so i also don't think this is
failing. Anyway the connection is established, and some packets are
exchanged.<br>
<br>Also remember that it works fine even from a linux client when having
both client and server on the same network (a lan, for
example).<br><br><br>Thanks in advance<br><br>
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