enq: US - contention
When you see enq: US - contention on Top 5 wait events on AWR or Statspack report or in ADDM findings you can take the following actions :
1) Check undo advisor if in 10g anf up.
2) Edit your undo retension parameter
3) Give space to Undo Tablespace
4) Move Undo tablespace to an other disk not so hot disk.
Mostly this wait event concerns autoxents on undo tablespaces.
A "db file sequential read" occurs when a an Oracle process looks for a block in the buffer cache and can’t find the block. The block is then read of disk, creating IO.
Db file sequential read wait time is increasing:
Check the average read times per file under FILE IO Stats
Check cache buffer hit ratio under "Buffer pool advisory"
1) Check undo advisor if in 10g anf up.
2) Edit your undo retension parameter
3) Give space to Undo Tablespace
4) Move Undo tablespace to an other disk not so hot disk.
Mostly this wait event concerns autoxents on undo tablespaces.
- db file sequential read and read by other session
A "db file sequential read" occurs when a an Oracle process looks for a block in the buffer cache and can’t find the block. The block is then read of disk, creating IO.
Db file sequential read wait time is increasing:
Check the average read times per file under FILE IO Stats
Check cache buffer hit ratio under "Buffer pool advisory"
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