Обсуждение: JDBC with PG 8.4 bytea character escaping wire protocol

Does the JDBC 4 driver for PG 8.4 escape each character of the bytea
type, or does it use a binary protocol?

 From another post, Merlin Moncure wrote, "libpq supports a binary
protocol mode which allows you to execute queries sending bytea without
escaping."  Is that true of the JDBC driver?  I'm concerned about the
data size expansion that would result for the wire protocol when I use
setBytes().

Thanks,
David

> Does the JDBC 4 driver for PG 8.4 escape each character of the bytea
> type, or does it use a binary protocol?
>
> From another post, Merlin Moncure wrote, "libpq supports a binary
> protocol mode which allows you to execute queries sending bytea
> without escaping."  Is that true of the JDBC driver?  I'm concerned
> about the data size expansion that would result for the wire protocol
> when I use setBytes().

I tried downloading the JDBC source and must say it was complex enough
to a newbie that I couldn't really determine the answer myself.    Does
anybody know if the JDBC driver with PG 8.4 communicates using a binary
protocol for BYTEA transfers to/from or whether it sends escaped chars
only?  Or perhaps which classes handle the transfer of BYTEA to PG and
receives BYTEA responses from PG?

Thanks,
David

On Thu, Oct 22, 2009 at 8:59 AM, David Wall <d.wall@computer.org> wrote:
>  Does anybody
> know if the JDBC driver with PG 8.4 communicates using a binary protocol for
> BYTEA transfers to/from or whether it sends escaped chars only?  Or perhaps
> which classes handle the transfer of BYTEA to PG and receives BYTEA
> responses from PG?

I don't know if you've already looked at this document (I'm not sure
if it answers your question):

http://jdbc.postgresql.org/documentation/84/binary-data.html

It sounds like it uses an InputStream but I'm not sure.

--
Regards,
Richard Broersma Jr.

Visit the Los Angeles PostgreSQL Users Group (LAPUG)
http://pugs.postgresql.org/lapug

> I don't know if you've already looked at this document (I'm not sure
> if it answers your question):
>
> http://jdbc.postgresql.org/documentation/84/binary-data.html
>
> It sounds like it uses an InputStream but I'm not sure.
>
Thanks, Richard. Yeah, I'm familiar with how to use them, but my
question is in regard to the wire transfer protocol between JDBC and the
PG backend.

David

On Thu, Oct 22, 2009 at 9:46 AM, David Wall <d.wall@computer.org> wrote:

> Thanks, Richard. Yeah, I'm familiar with how to use them, but my question is
> in regard to the wire transfer protocol between JDBC and the PG backend.

I'm guessing binary.

http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/jdbc/pgjdbc/org/postgresql/largeobject/BlobInputStream.java?annotate=1.12
http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/jdbc/pgjdbc/org/postgresql/largeobject/BlobInputStream.java?annotate=1.12


--
Regards,
Richard Broersma Jr.

Visit the Los Angeles PostgreSQL Users Group (LAPUG)
http://pugs.postgresql.org/lapug

I guess I can not really answer your question, since I have not dug
around in the code, but I can not understand
why the JDBC would escape a byte[] sent or received using the setBytes()
or getBytes() API or the stream
methods. These are binary protocols, which can house any integer value
within the limitations. The bytea
type is is defined as binary which means it does not necessarily
represent a character. Now the answer I guess
could be answered in two ways.

1. Someone here or yourself would have to know or dig through the code
to see if some conversion takes place.
2. Make a test case that sends or receives the data using
setBytes()/getBytes() and one of the APIs that
    does escape characters or you manually escape the characters. Use a
packet sniffer to check the package size
    in both cases. If they are the same then a conversion is taking
place. I would suspect the Bytes() method would
    result in less bandwidth, not more, no data size expansion.

danap

>> Does the JDBC 4 driver for PG 8.4 escape each character of the bytea
>> type, or does it use a binary protocol?
>>
>> From another post, Merlin Moncure wrote, "libpq supports a binary
>> protocol mode which allows you to execute queries sending bytea
>> without escaping."  Is that true of the JDBC driver?  I'm concerned
>> about the data size expansion that would result for the wire protocol
>> when I use setBytes().
>
>
> I tried downloading the JDBC source and must say it was complex enough
> to a newbie that I couldn't really determine the answer myself.
> Does anybody know if the JDBC driver with PG 8.4 communicates using a
> binary protocol for BYTEA transfers to/from or whether it sends
> escaped chars only?  Or perhaps which classes handle the transfer of
> BYTEA to PG and receives BYTEA responses from PG?
>
> Thanks,
> David

David Wall wrote:
> Does the JDBC 4 driver for PG 8.4 escape each character of the bytea
> type, or does it use a binary protocol?

When sending parameter data to the server, it uses the binary format.

When receiving results from the server, it uses the text format.

-O

Does the JDBC 4 driver for PG 8.4 escape each character of the bytea type, or does it use a binary protocol?

When sending parameter data to the server, it uses the binary format.

When receiving results from the server, it uses the text format.

Thanks, Oliver.  Well, I hadn't even thought it could be both. <smile> 

There was confusion in the other replies because they were looking at how the data moves from my code into the driver, but not how the driver communicates with the backend.  It was clear I could store binary data as I was doing that just fine, but the PG docs made it sound like much of my binary data would end up expanding because more than half of the range an octet may have requires escaping per http://www.postgresql.org/docs/8.4/static/datatype-binary.html:

Table 8-7. bytea Literal Escaped Octets

Decimal Octet Value	Description	Escaped Input Representation	Example	Output Representation
0	zero octet	E'\\000'	SELECT E'\\000'::bytea;	\000
39	single quote	'''' or E'\\047'	SELECT E'\''::bytea;	'
92	backslash	E'\\\\' or E'\\134'	SELECT E'\\\\'::bytea;	\\
0 to 31 and 127 to 255	"non-printable" octets	E'\\xxx' (octal value)	SELECT E'\\001'::bytea;	\001

I am thinking this should not be a real issue for me since I will be using LOs for by big objects and BYTEAs for the smaller objects.

Thanks again,
David