Обсуждение: setFetchSize() and preferQueryMode incompatible?
Hello all, I've been playing around a little with using preferQueryMode set to extendedForPrepared to avoid the multiple round trips to the server. The default setting is a significant performance impact if there is any meaningful network latency. We were also attempting to setFetchSize and found these two settings will not work together in any of the 42.2.1, 42.1.4 or 9.4.1202 jdbc client builds running against a 9.6.x version server. Is this a bug or a "feature"? Below is the sample code. The fetch size will not be respected with the preferQueryMode property present. Thank you for having a look. -- Alan public class Work { public static void main(String ... args) throws SQLException { // make obvious changes here.... String url = "jdbc:postgresql://host:5432/db"; String user = "user"; String passwd = "pass"; Properties props = new Properties(); props.put("user", user); props.put("password", passwd); props.put("preferQueryMode", "extendedForPrepared"); Connection conn = DriverManager.getConnection(url, props); conn.setAutoCommit(false); Statement st = conn.createStatement(); st.setFetchSize(1024); ResultSet rs = st.executeQuery("select * from reallyBigTable"); while (rs.next()) { rs.getObject(1); } } }
Hi,
TL;DR: it works as expected/designed.
Alan>extendedForPrepared to avoid the multiple round trips to the server.
The default setting is a significant performance impact if there is any
meaningful network latency
The default setting is a significant performance impact if there is any
meaningful network latency
Would you please elaborate and/or provide a test case for the "performance impact"?
Note: you might want to collect some trace logs (loggerLevel=TRACE&loggerFile=pgjdbc-trace.log) in order to count the roundtrips.
Alan>The fetch size will not be respected with the
preferQueryMode property presentThat setting means pgjdbc would use "Simple Query" to execute con.createStatement() kind of statements.
"Simple query" does not support portals, and there is no room to specify "fetch size".
It is just <<'Q' len:Int32 text:string>> message to the server, and it always replies with full set of rows.
In case you absolutely need to use preferQueryMode=extendedForPrepared, you can make fetchsize to work by using con.prepareStatement(...)
Vladimir