when we take a export dump with compress =y option, how does one get to know that the actual compression has taken place?
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when we take a export dump with compress =y option, how does one get to know that the actual compression has taken place?
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.
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
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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
compress=y is a no no option
AFAIK there is no DD views for this.Quote:
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
pando, please explain - txQuote:
Originally posted by pando
compress=y is a no no option
Oooh oooh! I know this one!Quote:
Originally posted by DaPi
pando, please explain - tx
compress=y leads to tablespace fragmentation by having different sized extents created on import.
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