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Re: OIDs - file objects, are damaged by PostgreSQL. - Mailing list pgsql-general

From Purusothaman A
Subject Re: OIDs - file objects, are damaged by PostgreSQL.
Date
Msg-id 3650d0d50705232254w265b94b0yaaf5163b92567403@mail.gmail.com
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In response to Re: OIDs - file objects, are damaged by PostgreSQL.  (Richard Huxton <dev@archonet.com>)
Responses Re: OIDs - file objects, are damaged by PostgreSQL.
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Richard Huxton,

Thanks for your detailed reply.

I am maintaining various database of same kind in postgresql.
Here I have shown various corrupted last line of output of select * from pg_largeobject where oid = xxxxxx; in 5 databases.

I have used '\o e:\\filename.xml' before executing query and inspected the output in that file.

Kindly look at the end of line in all 5 outputs.
First 3 output shows few missing characters.
But last 2 output is the perfect one.

1. Output of SFRS2 database:
--------------------------------------------
 101177 |    630 | ight_val></_></_></trees>\015\012      <stage_threshold>-2.9928278923034668</stage_threshold>\015\012      <parent>23</parent>\015\012      <next>-1</next></_></stages></haarcascade_frontalface_defau
(631 rows)

2. Output of SFRS1 database:
---------------------------------------------
 41642 |    630 | ight_val></_></_></trees>\015\012      <stage_threshold>-2.9928278923034668 </stage_threshold>\015\012      <parent>23</parent>\015\012      <next>-1</next></_></stages></haarcascade_frontalface_default>\015\012</openc
(631 rows)

3. Output of FASP_AVT database:
--------------------------------------------------
 101800 |    630 | ight_val></_></_></trees>\015\012      <stage_threshold>-2.9928278923034668</stage_threshold>\015\012      <parent>23</parent>\015\012      <next>-1</next></_></stages></haarcascade_frontalface_default>\015\012</openc
(631 rows)

4. Output of SFRS database: (not yet corrupted)
----------------------------------------------------------------------
 24038 |    630 | ight_val></_></_></trees>\015\012      <stage_threshold>- 2.9928278923034668</stage_threshold>\015\012      <parent>23</parent>\015\012      <next>-1</next></_></stages></haarcascade_frontalface_default>\015\012</opencv_storage>\015\012
(631 rows)

5. Output of FASP_TEST database: (Not yet corrupted)
--------------------------------------------------------------------------------
 106310 |    630 | ight_val></_></_></trees>\015\012      <stage_threshold>- 2.9928278923034668</stage_threshold>\015\012      <parent>23</parent>\015\012      <next>-1</next></_></stages></haarcascade_frontalface_default>\015\012</opencv_storage>\015\012
(631 rows)

Can you figure out the reason behind that.
I am waiting for your valuable suggestion.

Thanks.

Regards,
Purusothaman A

On 5/23/07, Richard Huxton <dev@archonet.com> wrote:
Purusothaman A wrote:
> Dear Richard Huxton,
>
> Thanks for your quick reply.
>
> only the first 3 values(HX, MASK, Rockey4ND) are file object's oid value.
> the other two are are not oid values.

Umm - OK. Can I suggest perhaps having different tables for different
types of data?

> I have shown original output values displayed by postgresql client.
>
> I can explain more.
>
> 1. HX is a XML file. after downloading that file I opened that file in word
> pad application.
> In that I have noticed that nearly 20 characters of last line lost.
> 2. Rockey4ND is a dll file. I was unable to use that dll in my application.
>
> In both cases, I checked file size. Corrupted files are smaller when
> compare
> to the original one what I uploaded to postgresql.

OK, so the data seems OK up until that point?

> Usually this problem arises only after the database become large.

I can't think of any reason why that would make a difference. But, this
does give us a clue. If you have successfully downloaded these files
before, that rules out certain forms of failure.

> Any suggestion to rectify this problem would be nice of you.

Reading through recent release notes, I can't see anything mentioning
lo_import/export, large objects or similar.

http://www.postgresql.org/docs/8.2/static/release-8-2-4.html

Well, your data is stored in pg_largeobject. If you run a SELECT you can
see how it's broken into chunks.
   SELECT loid,pageno,length(data) FROM pg_largeobject ;

On my system, a full chunk is 2048 bytes long. What does the last chunk
of your HX object (101800) look like? Is it a full chunk? Does it end
where your downloaded file ends?

If the data is OK in pg_largeobject then we know we have a problem with
lo_export-ing or saving to a file.

If not, then we know we have a problem with something deleting or
overwriting chunks in pg_largeobject. That would surprise me, because I
don't think there's anything special about pg_largeobject - it's just a
table with chunks of bytea data in it.

Just to recap - you're using lo_import() and lo_export from C (or at
least via libpq) to read/write these files directly to your filesystem.
You've not been seeing crashes and you don't think you've got hardware
problems.

--
   Richard Huxton
   Archonet Ltd



--
http://PurusothamanA.wordpress.com/

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