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Re: Bytea, ASCII-only encoding and pg_dumpall (Was: Bytea vs. BLOB)

From: Joe Conway <mail(at)joeconway(dot)com>
To: Frank Joerdens <frank(at)joerdens(dot)de>
Cc: pgsql-general(at)postgresql(dot)org, hank(at)fas-art(dot)com,adam(at)archi-me-des(dot)de
Subject: Re: Bytea, ASCII-only encoding and pg_dumpall (Was: Bytea vs. BLOB)
Date: 2002-03-31 16:08:07
Message-ID: 3CA73467.4080008@joeconway.com (view raw or flat)
Thread:
Lists: pgsql-general
Frank Joerdens wrote:
 > concatenated). What I don't understand yet is if that also applies if
 > you don't use ASCII-only encoding (how is data representet internally
 > without it?) and when you'd decide to encode or not, or if the fact
 > that you can dump to text would be sufficient grounds to decide to
 > encode everything bytea to ASCII-only.
 >

Actually, since bytea is truly treating the data as a string of bytes,
there is no notion of encoding at all. An input octet, say '\000' is 
turned into exactly one byte with a value of 0. In fact, the major 
diffenence between the "normal" (text, varchar, etc) functions and the 
bytea ones is that the bytea ones have the multi-byte encoding specific 
code removed.

A small experiment shows what the dump output would look like:

test=# CREATE TABLE foo2 (f1 bytea);
CREATE
test=# insert into foo2 values('\\003\\002\\001\\000abcdefg\\377');
INSERT 16594 1
test=# select f1 from foo2;
              f1
-----------------------------
  \003\002\001\000abcdefg\377
(1 row)

test=# select length(f1) from foo2;
  length
--------
      12
(1 row)

test=# \q
[postgres(at)jec-linux postgres]$ pg_dump -t foo2 test
--
-- Selected TOC Entries:
--
\connect - postgres

--
-- TOC Entry ID 2 (OID 16589)
--
-- Name: foo2 Type: TABLE Owner: postgres
--

CREATE TABLE "foo2" (
         "f1" bytea
);

--
-- Data for TOC Entry ID 3 (OID 16589)
--
-- Name: foo2 Type: TABLE DATA Owner: postgres
--


COPY "foo2" FROM stdin;
\\003\\002\\001\\000abcdefg\\377
\.


So it seems you can avoid a pg_dump -b by using bytea.

Regards,
Joe


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