Re: READ wait events when inserting data into a CLOB

  • From: Saibabu Devabhaktuni <saibabu_d@xxxxxxxxx>
  • To: free <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 5 Dec 2012 13:02:51 -0800 (PST)

You'd typically see "direct path" reads and writes for LOB insert operations if 
the lob is stored out of line or if the lob size exceed 4K. You may be getting 
"db file sequential read" waitevent for your indexes on the table. You'd also 
see "db file sequential read" waitevent for lobindex operations.

Another possibility is flashback feature requiring blocks to be read from the 
disk prior to performing block new operation.

I see below trace data very interesting, why same block is being read with "db 
file sequentially read" and "direct path read".

WAIT #139690535902720: nam='db file sequential read' ela= 321 file#=5 
block#956449 blocks=1 obj#425 tim54644922208727
WAIT #139690535902720: nam='direct path read' ela= 216 file number=5 first 
dba956449 block cnt=1 obj#425 tim54644922208998



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