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This error appears when I am trying to move LOB segment from one tablespace to another one.

Also during exporting the same error appears.

What can be a problem?

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As I found, I have corrupted lob segment. I know its rowid. Do I have a chance to recover it? – kupa Oct 28 '11 at 9:00
How did you diagnose the corruption? Recovery from corruption is generally by restore from backup but if there is an underlying issue (eg hardware problem), you need to resolve that first. – Jack Douglas Oct 28 '11 at 15:50
@JackDouglas It is very strange, when I use dbms_repair it doesn't show any corruption .. if I select table containing lob segment there is values in lob column <NCLOB> ... and one <Value Error> what is it? – kupa Oct 28 '11 at 16:19
using what client? – Jack Douglas Oct 28 '11 at 16:35
@JackDouglas do u mean the version? 10.2.0. I did the following workaround: updated these values by empty_clob() and after then I was able to move that table to another tablespace(it was definitely corrupted). But this is just a workaround not a solution – kupa Nov 1 '11 at 20:46
up vote 1 down vote accepted

Per the Oracle Docs and MetaLink support note 66431.1, the standard undo mechanism is not used by LOB segments, which have their own page versioning (controlled via PCTVERSION and the LOB_retention_clause).

"Snapshot too old" generally means that a transactionally-consistent version of your data could not be hold long enough because of lack of space. It might be that your PCTVERSION setting is too strict and effectively causes any new update to invalidate the consistent version(s).

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