For the record, 'db file sequential read' isn't ALWAYS a single-block read.
There are cases in which you can see 'db file sequential read' events with
p31. It happens (well, happened) when the kernel reads from a data file
directly into a user's non-shared process space (not the SGA). It used to
Good day all,
We have a bunch of queries in our data warehouse environment that are taking a long
time to complete.
I did a select on v$session_wait on one of the queries when it is running and it shows
the wait event to be 'db file sequential read', which means it is scanning index
blocks,
Dennis:
THe event 'db file sequential read' is NOT always an INDEX Scan. It is
just a single block read which TYPICALLY happens during an INDEX scan.
The word 'TYPICALLY' is the key here.
Best Regards,
K Gopalakrishnan
-Original Message-
Meng, Dennis
Sent: Wednesday, June 11, 2003
It's reads the block using the *ROWID*...that would explain his concerns...
Regis
-Original Message-
Sent: Wednesday, June 11, 2003 7:19 PM
To: Multiple recipients of list ORACLE-L
Dennis:
THe event 'db file sequential read' is NOT always an INDEX Scan. It is
just a single block read
A SINGLE block? I was convinced that it was = DB_FILE_MULTIBLOCK_READ_COUNT
blocks.
Are you sure?
Mladen Gogala
Oracle DBA
Phone:(203) 459-6855
Email:[EMAIL PROTECTED]
-Original Message-
Sent: Wednesday, June 11, 2003 2:19 PM
To: Multiple recipients of list ORACLE-L
Dennis:
THe event
The db file sequential read means that oracle is trying to read a sequence
of
consecutive blocks, shorter then DB_FILE_MULTIBLOCK_READ_COUNT. That usually
happens
when reading indexes, but it's not inconceivable to happen during table
access as well.
Mladen Gogala
Oracle DBA
Phone:(203) 459-6855
db file sequential read means single block read, which can be either from
an index or from a table. Likewise, db file scattered read means
multiblock read, which again can be either from a table or from an index.
At 10:01 AM 6/11/2003 -0800, you wrote:
Good day all,
We have a bunch of queries
Yes, 'db file sequential read' is always a single block read. It is 'db
file scattered read' which is = DB_FILE_MULTIBLOCK_READ_COUNT
At 10:35 AM 6/11/2003 -0800, you wrote:
A SINGLE block? I was convinced that it was = DB_FILE_MULTIBLOCK_READ_COUNT
blocks.
Are you sure?
Mladen Gogala
Oracle DBA
