On 23/03/17 04:24, Tom Dunstan wrote:
> Hi all
>
> I hit an interesting case today. It’s a bit of a limitation in the JDBC interface, so any support would have to be a
proprietaryinterface.
>
> Basically I have one or more byte buffers that I’d like to stream into a BYTEA at the server (using a plain INSERT
statement).In my case I’ve got Netty ByteBuf objects, but it could be anything.
>
> What are my current options? JDBC basically gives me PreparedStatement.setBytes() and
PreparedStatement.setBinaryStream().
>
> PreparedStatement.setBytes() involves copying all the data, potentially multiple large buffers, into a large buffer
ofexactly the correct size. The reason to use ByteBufs in the first place was to pool our use of large buffers so that
wedon’t blow out our heap - this completely kills any hope of that.
>
> PreparedStatement.setBinaryStream() is more flexible, but under the hood we’re just pulling stuff into an
intermediary8k buffer and then writing it out to the socket. This is OK from a heap management perspective, but still
hassome unnecessary copying.
>
> What I’d really like to do would be to provide an object that the driver could interrogate for a length and then
providean OutputStream to write to. The interface would look something like:
>
> interface ByteStreamWriter {
> int getLength();
> void writeTo(OutputStream stream);
> }
>
> The provided output stream would be a very thin wrapper around the socket output stream just ensuring that we don’t
writetoo many bytes out.
>
> Usage would look thusly:
>
> myPreparedStatement.setObject(n, new MyByteStreamWriter(myByteBuf), Types.VARBINARY);
>
> And the user could write whatever adapter they wanted around their data.
>
> There’s an existing StreamWrapper class in the codebase, but it just provides an InputStream when asked. It could be
adjustedto use the above interface for consistency though.
>
> Thoughts? I’d be happy to code up a PR if there’s interest.
>
> Cheers
>
> Tom
>
>
>
>
Hi Tom.
I think this is quite a good approach. I've seen significant
overheads in heap object creation in the process of
serialization/deserialization. Some of them were documented as part of
the slides of this talk:
https://www.slideshare.net/8kdata/java-and-postgresql-performance-features-and-the-future
(starting slide #19).
So having an adapter to write the data to the socket without
rewriting the bytes is a very desirable goal, in my opinion.
Cheers,
Álvaro
--
Álvaro Hernández Tortosa
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