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From:Martijn Tonies Date:February 12 2010 7:05am
Subject:Re: how things get messed up
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>>> [JS] Storing BLOBs in a table must slow down the inner workings of the
>>> database engine. After all, the tables are really disk files under the
>>> covers.
>>> Can the database engine read only parts of a file record?
>>>
>>> Jerry Schwartz
>>
>>Well, there's where things go wrong -- first of all, a "database engine"
>>can do -anything- it likes with the actual data.
>>
>>For example, the Firebird DBMS stores (longer) Blob data not right
>>there in the record, so whenever you don't request the blob (that is,
>>not selecting it), it ignores it completely and it can go through the file
>>quickly.
>>
> [JS] That's an interesting idea that hadn't occurred to me. Essentially, 
> it's
> creating a dependent table behind your back.
> Jerry Schwartz

Firebird uses 1 or multiple files per database, not per table, this file has
a special "blob area", so to speak, and the records include a "blob ID".

When a client/stored routine selects a blob that isn't available in the 
record
data (stored "in between"), it then goes to the area where blobs are stored
and gets it from there. Works quite well.

As I said, a DBMS can do anything it likes with it's data as long as it 
returns
it correctly.

I'm surprised there are DBMSses that don't do this, Firebird comes from
InterBase comes from Groton Database Systems which was the first
with BLOBs and they had the idea right, so it seems ;-) Enjoy the read:
http://www.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_blob_history


With regards,

Martijn Tonies
Upscene Productions
http://www.upscene.com

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Thread
how things get messed upJohn G. Heim10 Feb
  • Re: how things get messed upBuford Tannen10 Feb
  • RE: how things get messed upIlya Kazakevich10 Feb
    • Re: how things get messed upCui Shijun11 Feb
      • RE: how things get messed upJerry Schwartz11 Feb
        • Re: how things get messed upJohan De Meersman12 Feb
    • Re: how things get messed upJoerg Bruehe11 Feb
    • Re: how things get messed upJochem van Dieten11 Feb
  • Re: how things get messed upMartijn Tonies11 Feb
    • Re: how things get messed upDavid Giragosian11 Feb
  • RE: how things get messed upJerry Schwartz11 Feb
  • Re: how things get messed upMartijn Tonies11 Feb
    • RE: how things get messed upJerry Schwartz11 Feb
    • Re: how things get messed upAnn W. Harrison12 Feb
  • Re: how things get messed upMartijn Tonies12 Feb
    • Re: how things get messed upJohan De Meersman12 Feb
  • Re: how things get messed upMartijn Tonies12 Feb
    • Re: how things get messed upJohan De Meersman12 Feb
      • Re: how things get messed upVikram A12 Feb
        • Re: how things get messed upJohan De Meersman12 Feb
          • Re: how things get messed upVikram A12 Feb
            • RE: how things get messed upJerry Schwartz16 Feb
              • RE: how things get messed upMartin Gainty16 Feb
                • Re: how things get messed upBarry Leslie17 Feb
              • Re: how things get messed upVikram A18 Feb
                • RE: how things get messed upJerry Schwartz18 Feb
                  • Re: how things get messed upJohan De Meersman18 Feb
  • Re: how things get messed upMartijn Tonies15 Feb
  • Re: how things get messed upMartijn Tonies15 Feb
    • Re: how things get messed upJohan De Meersman16 Feb
      • Re: how things get messed upPaul McCullagh17 Feb
  • Re: how things get messed upMartijn Tonies15 Feb
    • Re: how things get messed upAnn W. Harrison15 Feb
      • Re: how things get messed upJohan De Meersman16 Feb
      • RE: how things get messed upJerry Schwartz16 Feb
  • Re: how things get messed upMartijn Tonies18 Feb
RE: how things get messed upJerry Schwartz22 Feb
  • Re: how things get messed upVikram A24 Feb