Blocks are read in their entirety and written in their entirety. There is a
header (small) in each block that holds the info about the block. There are
chapters on how it decides to write to a block that has data or a new one.
"Damian" <kndoneill_at_hotmail.com> wrote in message
news:Yc3Q5.31536$SF5.552348_at_ozemail.com.au...
> For curiosity's sake, I'd like to see the source code (fat chance I know).
> Therefore, as an exercise in reverse engineering, how would one go about
> updating a dbf file?
>
> SELECT Scenario
> Selects, updates and deletes would first require a file seek function. I
> quess you'd have to do a string search first to find the rowid.
>
> UPDATE Scenario
> Well I guess you'd open the dbf with file read, write flags set.
> Then you'd search thru the file sequentially, probably moving your file
> pointer every <block size> until you found your table from the table dir
> then row from row dir. Then delete <ROWID> from block, (then maybe) move
all
> data in block after the deletion up to where the rowid before the deleted
> one ends. finally, write your updated row at the end of the last row in
the
> block.
>
> INSERT Scenario
> Say a new row is to be inserted into the table.Is it going to be inserted
at
> the END of block (which?) assigned for the Table. What will happen if the
> Block is consumed and a new block is going to be created. Where the new
> block is going to be created and how it will effect the performance when
the
> blocks are split across separated by different blocks.
>
> DELETE Scenario:
> Same as update without the write function at the end.
>
> "Barbara Kennedy" <barbken_at_teleport.com> wrote in message
> news:D61Q5.10839$au.438196_at_nntp3.onemain.com...
> > If you are just looking for it conceptually the manual (available in
Html
> > format on the CD ) Oracle Concepts manual. If you are asking so you can
get
> > at the data directly then don't do it! If you need to get at the data
> > directly (by scanning the file directly) write your own dbms; don't use
a
> > commercial dbms and try to subvert it. You will only cause yourself
great
> > pain. The manuals don't go into enough details to reverse engineer it.
> > Jim
> > "Pravesh Godiyal" <namia_at_hotmail.com> wrote in message
> > news:Sj0Q5.31459$SF5.549328_at_ozemail.com.au...
> > > Is there any one aware or could share the knowledge as how oracle
store
the
> > > table-reocrds into dbf files.
> > > How it access the data in the dbf files.
> > >
> > > Cheers
> > > Namia
> > >
> > >
> >
> >
>
>
Received on Tue Nov 14 2000 - 00:07:21 CST
