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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-5066) full table scan when index is used, taking extremely long time in JDBC
Date Fri, 25 Feb 2011 05:17:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12999219#comment-12999219
] 

Mike Matrigali commented on DERBY-5066:
---------------------------------------

there is probably some tuning that could be done on the sort, as bryan mentions.  It could
be you need to start your jvm with some bigger initial heaps.  But as I understand the goal
of the app derby is never going to give you what you are looking for if it does a sort rather
than
do sort avoidance.

You have 3 choices:
1) assuming PID is a unique key, first issue an order select to get all the PID's of interest
and then as you fill each row in the UI do a stored prepared statement to look up the data
associated with the PID.  I believe if you just select the stuff in the index it will never
do a sort.

2) use optimizer hints to force the use of the index in your query.

3) use fetch/offset feature added recently to derby to get "chunks" of data.  I don't know
much about this feature so am not sure if it will avoid
     the sort or not.  

> full table scan when index is used, taking extremely long time in JDBC
> ----------------------------------------------------------------------
>
>                 Key: DERBY-5066
>                 URL: https://issues.apache.org/jira/browse/DERBY-5066
>             Project: Derby
>          Issue Type: Bug
>          Components: Eclipse Plug-in, JDBC
>    Affects Versions: 10.7.1.1
>         Environment: Windows XP environment
>            Reporter: George Xu
>         Attachments: LogXData.rar
>
>
> When a very large table (500k rows) is used with a column is indexed.   select * from
tab where pid > 0 order by pid takes extremely longer time than select * from tab order
by pid.  Actually, it is 100 times slower.  However, in IJ, ther performance seems to be similar.
 PID column is indexed.
> Here is the code snipplet
> import java.sql.Connection;
> import java.sql.DriverManager;
> import java.sql.ResultSet;
> import java.sql.SQLException;
> import java.sql.Statement;
> public class TestPerformance {
> 	//20343 mill-sec
> 	static String s1 = "SELECT TIMESTAMP, HOSTPORT AS \"HOST ID\", PID, SESSIONID, REQUESTID,
" +
> 	"SUBREQUESTID, STEPID, TID, COMPONENT, BUILDNUM, " +
> 	"LOGLEVELORIG AS \"LEVEL\", LOGGER, OPERATION, OBJECTTYPE, OBJECTPATH, " +
> 	"STATUS, MESSAGE, DATA, NDX FROM LOGDATA871218 where PID > 0 ORDER BY PID";	
> 	//297 million sec.
> 	static String s2 = "SELECT TIMESTAMP, HOSTPORT AS \"HOST ID\", PID, SESSIONID, REQUESTID,
" +
> 	"SUBREQUESTID, STEPID, TID, COMPONENT, BUILDNUM, " +
> 	"LOGLEVELORIG AS \"LEVEL\", LOGGER, OPERATION, OBJECTTYPE, OBJECTPATH, " +
> 	"STATUS, MESSAGE, DATA, NDX FROM LOGDATA871218 ORDER BY PID";	
> 	public static void main(String[] args) throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
> 		Statement stmt3;
> 		try {
> 			//connect'jdbc:derby:C:/devroot/runtime-New_configuration/LogXData';
> 			String db = "C:/devroot/runtime-New_configuration/LogXData";
> 			String driver = "org.apache.derby.jdbc.EmbeddedDriver";
> 			Class.forName(driver).newInstance();
> 			Connection con = DriverManager.getConnection("jdbc:derby:"+db);			
> 			stmt3 = con.createStatement(ResultSet.FETCH_FORWARD, 
> 			        ResultSet.TYPE_FORWARD_ONLY);
> 			long startTime3 = System.currentTimeMillis();
> 			ResultSet rs3 = stmt3.executeQuery(s1); 
> 			long elapsed3 = System.currentTimeMillis() - startTime3;
> 			System.out.println("Statment.executeQuery Dup: " + elapsed3); 
> 		} catch (SQLException e) {
> 			// TODO Auto-generated catch block
> 			e.printStackTrace();
> 		}			
> 	}
> }

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