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Re: bytea memory improvement

From:	Luis Vilar Flores <lflores(at)evolute(dot)pt>
To:	Kris Jurka <books(at)ejurka(dot)com>
Cc:	pgsql-jdbc(at)postgresql(dot)org
Subject:	Re: bytea memory improvement
Date:	2006-09-26 10:09:10
Message-ID:	4518FC46.8020705@evolute.pt
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Kris Jurka wrote:
<blockquote cite="midPine(dot)BSO(dot)4(dot)63(dot)0609260131040(dot)29854(at)leary2(dot)csoft(dot)net"
type="cite"> 
 
On Wed, 23 Aug 2006, Luis Vilar Flores wrote:
 
 
<blockquote type="cite">  To all that already forgot the first
emails, I developed an modified version of the method toBytes from the
org.postgresql.util.PGbytea class.  The old method uses 3 buffers to
translate the data from the nework to the client, this uses too much
memory.  My method only uses 2 buffers, but does one more pass through
the original buffer (to calculate it's final size).
 
 
</blockquote>
 
I'm not super impressed with these timing results.  They are certainly
showing some effects due to GC, consider the rise in time here at
10.5MB.
 
</blockquote>
Well, thanks a lot for the attention. My main purpose was to reduce the
memory footprint. But, before I did the tests, I had the idea that the
new method would be slower than the older ... So it would only be
better on large files, i.e. where the reduced memory usage was more
important than raw speed. This was because of the extra cycle through
the array. 
<blockquote cite="midPine(dot)BSO(dot)4(dot)63(dot)0609260131040(dot)29854(at)leary2(dot)csoft(dot)net"
type="cite"> 
<blockquote type="cite">OLD method:
 
size: 9.5MB execute+next: 804ms getBytes: 377ms used mem: 66169KB
 
size: 10.5MB execute+next: 634ms getBytes: 546ms used mem: 73112KB
 
size: 11.5MB execute+next: 689ms getBytes: 450ms used mem: 80057KB
 
size: 12.5MB execute+next: 748ms getBytes: 482ms used mem: 87001KB
 
</blockquote>
 
I came up with my own contrived benchmark (attached) that attempts to
focus solely on the getBytes() call and avoid the time of fetching
results, but it doesn't give really consistent results and I haven't
been able to come up with a case that actually shows the new method was
faster even with 30MB of data.  This is on Debian Linux / 2xOpteron 246
/ jdk 1.5.0-05.
 
</blockquote>
The new method is very similar to the old, but it just computes the
final size before the copy. The old method does less instructions to
convert an array, the new method is only faster when the older is
slowed down by garbage collection/memory allocation. 
<blockquote cite="midPine(dot)BSO(dot)4(dot)63(dot)0609260131040(dot)29854(at)leary2(dot)csoft(dot)net"
type="cite"> 
I've committed this to CVS HEAD with a rather arbitrarily set
MAX_3_BUFF_SIZE value of 2MB.  Note that this is also the escaped size,
so we may actually be dealing with output data a quarter of that size. 
If anyone could do some more testing of what a good crossover point
would be that would be a good thing.
 
</blockquote>
I think the old option should be there for a while, but I hope that the
new method proves to be as fast as the old, so we can just discard the
MAX_3_BUFF_SIZE and always compute the final size - as the method code
would be clearer that way. 
<blockquote cite="midPine(dot)BSO(dot)4(dot)63(dot)0609260131040(dot)29854(at)leary2(dot)csoft(dot)net"
type="cite"> 
Thanks for your patience with this item.
 
</blockquote>
It's me who thanks for such a great product ... 
I will check the new benchmark, the see the memory usage, and garbage
collection ... 
<blockquote cite="midPine(dot)BSO(dot)4(dot)63(dot)0609260131040(dot)29854(at)leary2(dot)csoft(dot)net"
type="cite"> 
Kris Jurka 
<pre wrap="">
<hr size="4" width="90%">
import java.sql.*;

public class ByteaTest2 {

public static void main(String args[]) throws Exception {
Class.forName("org.postgresql.Driver");
Connection conn = DriverManager.getConnection("jdbc:postgresql://localhost:5432/jurka","jurka","");

for (int k=0; k<5; k++) {
long t1 = System.currentTimeMillis();
long total = 0;

for (int j=0; j<10; j++) {
PreparedStatement pstmt = conn.prepareStatement("SELECT varcharsend(repeat(?,?))");
pstmt.setString(1, "a\\001");
pstmt.setInt(2, 150000);
ResultSet rs = pstmt.executeQuery();
rs.next();
for (int i=0; i<100; i++) {
byte b[] = rs.getBytes(1);
total += b.length;
}

rs.close();
pstmt.close();
}
long t2 = System.currentTimeMillis();
System.out.println(t2-t1);
}
}
}
</pre>
</blockquote>
 
 
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<title>Evolute - Luis Flores</title>
 Luis Flores


 Analista de Sistemas
<a href="http://www.evolute.pt">Evolute - Consultoria
Informática 
 
</a>
 Email: 
<a href="mailto:lflores(at)evolute(dot)pt">lflores(at)evolute(dot)pt
</a>

 Tel: (+351)
212949689
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Re: bytea memory improvement at 2006-09-26 06:53:06 from Kris Jurka

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