Re: [JDBC] Postgresql JDBC UTF8 Conversion Throughput

From: Kris Jurka <books@ejurka.com>

Date: September 19, 2008 12:29:45 AM PDT

To: Paul Lindner <lindner@inuus.com>

Cc: pgsql-jdbc@postgresql.org

Subject: Re: Postgresql JDBC UTF8 Conversion Throughput

On Mon, 2 Jun 2008, Paul Lindner wrote:

It turns out the using more than two character sets in your Java

Application causes very poor throughput because of synchronization

overhead.  I wrote about this here:

http://paul.vox.com/library/post/the-mysteries-of-java-character-set-performance.html

Very interesting.

In Java 1.6 there's an easy way to fix this charset lookup problem.

Just create a static Charset for UTF-8 and pass that to getBytes(...)

instead of the string constant "UTF-8".

Note that this is actually a performance hit (when you aren't stuck doing charset lookups), see

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6633613

For backwards compatibility with Java 1.4 you can use the attached

patch instead.  It uses nio classes to do the UTF-8 to byte

conversion.

This is also a performance loser in the simple case.  The attached test case shows times of:

Doing 10000000 iterations of each.
2606 getBytes(String)
6200 getBytes(Charset)
3346 via ByteBuffer

It would be nice to fix the blocking problem, but it seems like a rather unusual situation to be in (being one charset over the two charset cache). If you've got more than three charsets in play then fixing the JDBC driver won't help you because at most it could eliminate one.  So I'd like the driver to be a good citizen, but I'm not convinced the performance hit is worth it without having some more field reports or benchmarks.

Maybe it depends how much reading vs writing is done.  Right now we have our own UTF8 decoder so this hit only happens when encoding data to send it to the DB.  If you're loading a lot of data this might be a problem, but if you're sending a small query with a couple of parameters, then perhaps the thread safety is more important.

Hi Kris,

getBytes(String) when using a constant string will always win.  StringCoding.java (see http://www.docjar.net/html/api/java/lang/StringCoding.java.html)  caches the charset locally.

When you use 2 or more character sets getBytes(Charset) and getBytes(String) single-thread performance are about the same with getBytes(String) slightly ahead.  ByteBuffer ends up being the big winner:

Doing 10000000 iterations of each for string - 'abcd1234'

15662 getBytes(Charset)

14958 getBytes(String)

10098 via ByteBuffer

In any case all of this only pertains to single thread performance.  Our web apps are running on 8 and 16 core systems where contention is the biggest performance killer.