Обсуждение: Cannot Retrieve Binary Data
Hi all , i'm following the example at http://www.postgresql.org/docs/7.4/interactive/jdbc-binary-data.html trying to retrieve previous stored file (more than 600MB) using the following code: Jdbc3ConnectionPool source = new Jdbc3ConnectionPool(); conn = DriverManager.getConnection("jdbc:postgresql://localhost/backup", "test", "test"); conn.setAutoCommit(false); PreparedStatement ps = conn.prepareStatement("SELECT img FROM images WHERE imgname = ?"); ps.setString(1, "civil.dmg"); ResultSet rs = ps.executeQuery(); if (rs != null) { while (rs.next()) { byte[] imgBytes = rs.getBytes(1); // use the data in some way here } rs.close(); } ps.close(); conn.commit(); during the executeQuery() i got a the following exception java.sql.SQLException: ERROR: invalid memory alloc request size 2017394403 The Postgres version is 8.0.1 (compiled from source with default settings ) running on Darwin Kernel Version 7.8.0 Thanks in advance for any help -patrick
Exactly the same error:
ERROR: XX000: invalid memory alloc request size 2017394403
LOCATION: MemoryContextAlloc, mcxt.c:502
the table is declared as:
backup=# \d images;
Table "public.images"
Column | Type | Modifiers
---------+-------+-----------
imgname | text |
img | bytea |
and the query is (there's only one record)
backup=# SELECT img from images ;
ERROR: invalid memory alloc request size 2017394403
There's no way to stream a bytea ? how postgres support bytea with 1G
if is not possible to insert and select ?
FYI:
i tried the same Test with postgres 7.4.7 and earlier and is even worst
i was not able to insert.
The JDBC Driver Return Out_Of_Memory during the query execution
On 11 Mar 2005, at 22:05, Oliver Jowett wrote:
> patrick wrote:
>
>> i'm following the example at
>> http://www.postgresql.org/docs/7.4/interactive/jdbc-binary-data.html
>> trying to retrieve previous stored file (more than 600MB)
>
>> during the executeQuery() i got a the following exception
>> java.sql.SQLException: ERROR: invalid memory alloc request size
>> 2017394403
>
> What happens if you run an equivalent query via psql?
>
> I suspect what is happening is that you inserted the data earlier fine
> as JDBC sends it directly in binary form; however, when retrieving,
> the data asks for the text form, which expands the data by up to a
> factor of 5 (to >3GB for your file). The backend doesn't stream this
> data AFAIK, so it has to allocate space for the entire text
> representation. Then you hit a memory allocation sanity check in the
> backend, resulting in the error you see.
>
> -O
>
patrick wrote: > There's no way to stream a bytea ? how postgres support bytea with 1G if > is not possible to insert and select ? You need to use the binary parameter/result format (at the protocol level). The current JDBC driver uses the binary format for bytea parameters, but the text format for resultsets. psql uses the text format for both, I believe. > FYI: > i tried the same Test with postgres 7.4.7 and earlier and is even worst > i was not able to insert. > The JDBC Driver Return Out_Of_Memory during the query execution I assume you mean with an earlier version of the driver? Earlier driver versions used the text format for both parameters and results, and also used a large amount of temporary heap space for large bytea parameters. You may want to look at using the large-object interface if you are dealing with extremely large data; it allows random read/write access to the data without transferring it all across the wire in one go. -O
On 13 Mar 2005, at 13:36, Oliver Jowett wrote: > > You need to use the binary parameter/result format (at the protocol > level). The current JDBC driver uses the binary format for bytea > parameters, but the text format for resultsets. psql uses the text > format for both, I believe. Thanks for the suggestion i will try again >> FYI: >> i tried the same Test with postgres 7.4.7 and earlier and is even >> worst i was not able to insert. >> The JDBC Driver Return Out_Of_Memory during the query execution > > I assume you mean with an earlier version of the driver? Earlier > driver versions used the text format for both parameters and results, > and also used a large amount of temporary heap space for large bytea > parameters. both earlier driver and earlier version of postgresql now i undestand why my tests were failing. > You may want to look at using the large-object interface if you are > dealing with extremely large data; it allows random read/write access > to the data without transferring it all across the wire in one go. Yes it appear the be the best solution.. thanks for you help -patrick
I have also noticed that jdbc driver seems to be able to store larger binary objects than it can retrieve when using a bytea column.
Is there any guidance on what the recommended maximum size would be for a bytea column before moving to an OID column .. or is this dependant on tuning database server parameters?
-----Original Message-----
From: patrick [mailto:pch@freeshell.org]
Sent: 14 March 2005 07:34
To: pgsql-jdbc@postgresql.org
Subject: Re: [JDBC] Cannot Retrieve Binary Data
On 13 Mar 2005, at 13:36, Oliver Jowett wrote:
>
> You need to use the binary parameter/result format (at the protocol
> level). The current JDBC driver uses the binary format for bytea
> parameters, but the text format for resultsets. psql uses the text
> format for both, I believe.
Thanks for the suggestion i will try again
>> FYI:
>> i tried the same Test with postgres 7.4.7 and earlier and is even
>> worst i was not able to insert.
>> The JDBC Driver Return Out_Of_Memory during the query execution
>
> I assume you mean with an earlier version of the driver? Earlier
> driver versions used the text format for both parameters and results,
> and also used a large amount of temporary heap space for large bytea
> parameters.
both earlier driver and earlier version of postgresql now i undestand
why my tests were failing.
> You may want to look at using the large-object interface if you are
> dealing with extremely large data; it allows random read/write access
> to the data without transferring it all across the wire in one go.
Yes it appear the be the best solution.. thanks for you help
-patrick
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