IO bandwidth during direct read/write operations
- From: "Hameed, Amir" <Amir.Hameed@xxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 11 May 2007 11:12:29 -0400
Folks,
During Oracle's direct path operations (direct read, direct write, hash
joins, etc.), there are certain init parameters that govern the
bandwidth of the IO size that Oracle processes. It seems that even
though _db_file_direct_io_count is set to 1M, trace files of PQ slaves
show that Oracle still reads MRBC*DB_BLOCK_SIZE during the
non-hash-join/non-sort based direct read operations because on my system
with MRBC=8 and DB_BLOCK_SIZE=8k, p3 consistently showed up as 8 or
less.
There are two other parameters _smm_auto_min_io_size and
_smm_auto_max_io_size that limits the min and max size of IO used by
sort and hash-join operations and defaults to 56k and 248k respectively.
From the trace files, I have seen values of p3=31, which translates to
248k with MRBC set to 8.
Having said that, I just wanted to get confirmation that:
- the _smm_auto_min_io_size and _smm_auto_max_io_size parameters
only play role during the sort and hash-join operations
- the direct path read size (non sort and non-hash-join) is
still governed by the value of MRBC.
The DB versions are 9.2.0.6 and 10.2.0.2 (both 64-bits)
Thanks
Amir
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