Subject: How to determine cause of performance problem?
From: Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>
To: Pgsql-Performance <pgsql-performance@postgresql.org>
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Date: Fri, 23 Sep 2005 08:49:27 +0200
Message-Id: <1127458167.2475.105.camel@Panoramix>
Mime-Version: 1.0

Hi,

I must convert an old table into a new table. The conversion goes at ~
100 records per second. Given the fact that I must convert 40 million
records, it takes too much time: more hours than the 48 hour weekend I
have for the conversion;-).

The tables are rather simple: both tables only have a primary key
constraint (of type text) and no other indexes. I only copy 3 columns. I
use Java for the conversion. For the exact code see below.

During the conversion my processor load is almost non existant. The
harddisk throughput is ~ 6 megabyte/second max (measured with iostat).

My platform is Debian Sarge AMD64. My hardware is a Tyan Thunder K8W
2885 motherboard, 2 Opteron 248 processors, 2 GB RAM, a SATA bootdisk
with / and swap, and a 3Ware 9500S-8 RAID-5 controller with 5 attached
SATA disks with /home and /var. /var contains *all* PostgreSQL log and
database files (default Debian installation).

Output of hdparm -Tt /dev/sdb (sdb is the RAID opartition)

/dev/sdb:
 Timing cached reads:   1696 MB in  2.00 seconds = 846.86 MB/sec
 Timing buffered disk reads:  246 MB in  3.01 seconds =  81.79 MB/sec


I want to determine the cause of my performance problem (if it is one).

1. Is this a performance I can expect?
2. If not, how can I determine the cause?
3. Can I anyhow improve the performance without replacing my hardware,
e.g. by tweaking the software?
4. Is there a Linux (Debian) tool that I can use to benchmark write
performance?


-- 
Groeten,

Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J.Kraaijeveld@Askesis.nl
web: www.askesis.nl 


The Java code I use for the conversion  :

//////////////// ....
ResultSet resultSet = selectStatement.executeQuery(
"select ordernummer, orderdatum, klantnummer from odbc.orders order by
ordernummer");
			
connection.setAutoCommit(false);
			
PreparedStatement ordersInsertStatement = 
connection.prepareStatement("insert into prototype.orders
(objectid,ordernumber,orderdate,customernumber) values (?,?,?,?)");			
			
while( resultSet.next() )
{

if( (++record % 100) == 0){
	System.err.println( "handling record: " + record);
}
				
// the next line can do > 1.000.000 objectId/sec
String orderObjectId = ObjectIdGenerator.newObjectId();
ordersInsertStatement.setString(1,orderObjectId);
ordersInsertStatement.setInt(2,resultSet.getInt("ordernummer")); 
ordersInsertStatement.setDate(3,resultSet.getDate("orderdatum")); 
ordersInsertStatement.setInt(4,resultSet.getInt("klantnummer")); 
		
ordersInsertStatement.execute();
				
}	
			
connection.commit();