Re: EXP with compress=Y

On Mar 7, 6:07 am, "Oracle Data Miner" <shyamva..._at_gmail.com> wrote:
> On Mar 7, 6:09 am, "sybrandb" <sybra..._at_gmail.com> wrote:
>
>
>
>
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> > On Mar 7, 11:53 am, OleHa..._at_gmail.com wrote:
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> > > I have made a test of EXP with compress=Y and compress=N.
>
> > > The result was 2 dumpfile of the same size. (500 Mbytes).
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> > > Doesn't the compress parameter make the dumpfile smaller ?
>
> > > Regards,
> > > Ole
>
> > No
>
> > Please read the docs, and don't ask questions for you can find the
> > answer yourself in less than 5 minutes.
>
> > --
> > Sybrand Bakker
> > Senior Oracle DBA
>
> Compress = Y is to compress the extends of the table in the dmp file
> and not to compress the .dmp file. You can pipe the exp process to a
> compress (zip) process to compress the size in real time
> Thanks
> Shyam

Actually, if you read the docs, it doesn't compress the extents, but rather makes the initial extent into one really huge extent. This is very misleading, since that isn't what is done with LMT's when you do the import. It is entirely possible to make a very _oversized_ table when you do the import. Of course, if you actually try it with those settings, you may find it actually uses the real initial rather than doing any consolidation (I just tried compress=y on a large 9206 LMT table in an autoallocate tablespace, and it gave an initial of 65536).

So it really depends on versions and configurations, and the docs may be wrong or misleading. You must both understand and try it.

The better way to do it is to use COMPRESS=N, and either be sure the INITIAL parameter is reasonable before exporting, or precreate the tables with proper storage parameters before importing. (Personally, I prefer the latter, even if there are many tables).

Note you can see what the initial is with the imp indexfile command. You can also run strings on the dump file if you happen to have that command available, and examine storage parameter statements directly.

jg

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