export dump

[sharmila]

when we take a export dump with compress =y option, how does one get to know that the actual compression has taken place?

[agasimani]

When you export to dump file with compress=y, EXPORT utility modifies the INITIAL value of the table to be the sum of the current extents. So that means if the table has 50 * 10K extents filled, then the INITIAL extent when you IMPORT the data will be 500K.

[sharmila]

thanks , i very well know that this is what happens, but what i was wondering is that how do one come to know that such a option is used,, any query , DD views to tell us that compress =y has taken effect

[bang_dba]

.

[bang_dba]

check dba_extents.bytes and compare with the older value.

By default compress=y
if u want to retain the old storage values say compress=no

[pando]

compress=y is a no no option

[Giani]

Originally posted by sharmila
... but what i was wondering is that how do one come to know that such a option is used,, any query , DD views to tell us that compress =y has taken effect

AFAIK there is no DD views for this.

[DaPi]

Originally posted by pando
compress=y is a no no option

pando, please explain - tx

[slimdave]

Originally posted by DaPi
pando, please explain - tx

Oooh oooh! I know this one!

compress=y leads to tablespace fragmentation by having different sized extents created on import.

[pando]

if you understand well delete, truncate, segments and extents you will see why

if I have 100 extents with 1MB each but there are only 1MB real data what happens if I export with compress=y? I will get one 100MB extent 99% empty, if I use compress=n what happens? I get 1extent of 1MB, I saved 99MB