Re: Snapshot too old from READ-ONLY table (data pump export)
- From: Saibabu Devabhaktuni <saibabu_d@xxxxxxxxx>
- To: free <oracle-l@xxxxxxxxxxxxx>
- Date: Sat, 16 Jul 2011 12:03:45 -0700 (PDT)
Which version of Oracle are you using?
When the tablespace is in read only mode, delayed block cleanout is performed
but the dirty buffers will not be written to disk. Same is not true for read
only tables.
More on this
at http://sai-oracle.blogspot.com/2010/05/read-only-tables-in-11g-is-not-fully.html
If you were to select the records from the block you got ORA-1555, by using
rowid predicate instead, you wouldn't have gotten ORA-1555. Oracle is trying to
update ITL in block header with the minimum SCN of all the transactions
available in the undo segments, since your export datapump is running longer
than the undo retention, you are getting this error. Try running export
datapump with parallel threads.
There is a concept of "min active scn" introduced in 11g which is supposed to
enhance delayed block cleanout operations.
But in reality, Oracle shouldn't even need to do the delayed block cleanout on
*sufficiently* old blocks (determined by min active scn - which is supposed to
be minimum scn of all active transactions). I opened enhancement request on
this last year, Oracle support opened bug# 9941362 for this issue (hopefully
they fix it in 12g).
Thanks,
Sai
http://sai-oracle.blogspot.com
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