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From Knut Anders Hatlen <Knut.Hat...@Sun.COM>
Subject Re: network server overhead
Date Sun, 29 Jul 2007 19:54:38 GMT
Daniel John Debrunner wrote:
> I ran a simple test of executing VALUES 1 using a prepared statement 
> over the network server in auto-commit mode. 10.3 seemed to be the same 
> performance as 10.2, maybe up to 4% slower. The 10.2 numbers for me were 
> consistent, but the 10.3 numbers seemed to vary from 96% to 100% of the 
> 10.2 numbers.
> 
> I was actually surprised because I thought I seen some claims of much 
> faster performance with 10.3 server.

I don't remember seeing any performance improvements specific to the 
network server code being checked in during the 10.3 development.

> I was getting around 1,630 transactions per second (each transaction is 
> a VALUES 1 statement) on a 100Mbit network.
> 
> Did anyone make changes in 10.3 that they think would make this simple 
> test improve,

Shouldn't the VALUES 1 test benefit from DERBY-827?

 > or is anyone working on reducing the basic overhead for
> client server? Are the nio changes intended to improve performance?

I did some profiling of the network server (trunk, not 10.3) two weeks 
ago to see if something jumped at me. I used a similar test with VALUES 
1 using prepared statement, as well as a test which returned a 
varchar(100) column. The motivation for the nio changes was that I 
noticed that temporary byte arrays were created each time DDMWriter 
wrote a string, whereas nio allowed encoding directly into the output 
buffer. For a query that returned a string of 100 ASCII characters, this 
change reduced the object allocations with ~600 bytes/query according to 
DTrace.

I also noticed that most of the network server's CPU went into 
SocketInputStream.read() (big surprise...), so I experimented with 
replacing the use of Socket and InputStream in DDMReader with 
SocketChannel and direct ByteBuffer (which is supposed to reduce 
internal copying between buffers), but I didn't see any effect of that 
change.

I don't have the profiling data here right now, but I can post them on 
the wiki when I get back from vacation in two weeks, to let others see 
if they can get something out of the numbers.

-- 
Knut Anders

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