Re: expdp dump file and CLOB column

Mladen Gogala schrieb:
I have to import a 9GB dump file produced by expdp. My problem is space allocation. One of the columns is of the CLOB type and, for some reason, it produced a 45GB LOB segment. The obvious question is how do 45GB fit into 9GB export file? Is there an underlying compression? Are LOB objects in data pump dump files compressed? The logic tells me that they must be but I was unable to find any documentation. Does anybody have more info?




What is Oracle version you are speaking about?
I did some very basic tests on 10.2.0.4 and couldn't see anything similar to compression. I assumed, compression rate should be (doesn't matter what compression method is used) highest for most redundant data - in my testcase dumpfile size was the same for clobs filled either with dbms_random or with blanks. What size return sum(dbms_lob.getlength(lob_column)) ?
Does it nearly correlate with 45Gb ? If not, i would assume a massive space overallocation ( for whatever reason) during import. Another points to consider could be of course the charactersets on both source and target database and the original size of lob segments in the source.

If you are on 11g however - and export was done with data compression option,i would not wonder about compression rate, as it depends massively on your data pattern.

Best regards

Maxim
.

Relevant Pages

  • Re: [Info-Ingres] Clob table compression
    ... We have CLOB tables that store large XML strings. ... Subject: Clob table compression ... Does anyone know if data compression on a LOB table also compresses ... assumption would be that only the last LOB segment is likely to be ...
    (comp.databases.ingres)
  • Re: Disk Utility/encrypted images - choices
    ... But the main reason people use disk images is to protect their ... There may be some reasons not to bother with compression. ... likely people are going to use their backup device more frequently. ...
    (comp.sys.mac.system)
  • Re: Probability, compressible sequences: Backgrounds
    ... are in random domain or not without uncertainty. ... reason why compression still improves somewhat is that we *do* find ... you know that arithmetic compression is ... "almost" an IID generalized Gaussian statistics you see there). ...
    (comp.compression)
  • your assistance is requested
    ... (By the way, by 'compression', I mean that a typical input byte is ... I have some reason to think this question is my last technical problem ... At present I simulate input from an actual RAD source by AND'ing 255 & ... containing two bits less than the original inut value. ...
    (comp.compression)
  • Re: Javascript Library
    ... elements, showing/hiding objects, animating objects, ajax, etc? ... it makes the standard GZIP compression less effective. ... Using Packer will slow things down. ... Another reason that nobody uses Packer. ...
    (comp.lang.javascript)