Brave new stats in 11.1.0.7
Mladen Gogala
"fastpath" mechanism for consistent gets. There are 2 types
of fastpath consistent gets, one for the db blocks, one apart from that
one, probably for the index blocks. That would be consistent
with Jonathan's and Alex Fatkulin's blogs which have recently blogged
about "consistent gets from cache (fastpath)" statistics.
Now, consistent gets are at the basis of how Oracle RDBMS functions: when
returning data from a query, Oracle rebuilds the blocks
from the UNDO segments so that they are consistent with last transaction
committed before the query had started. That process of
rebuilding the blocks to the consistent state is called "a consistent
get". Consistent gets are an essential part of Oracle RDBMS ever
since Oracle 6. Before that, there was no UNDO tablespace but so called
"BI file", but let me digress no more.
This mechanism is so basic and essential that every change raises an
alarm flag. I would like someone from the Oracle Corp. to explain
the new mechanism and alleviate our stress. The illustration of the new
statistics is below:
[oracle@dibidus2 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.1.0.7.0 - Production on Mon Jan 26 11:16:54 2009
Copyright (c) 1982, 2008, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing
options
SQL> select name,value from v$sysstat
2 where name like '%fast%';
NAME
VALUE
----------------------------------------------------------------
----------
db block gets from cache (fastpath)
1117557
consistent gets from cache (fastpath)
17950678
index fast full scans (full)
9201
index fast full scans (rowid ranges)
0
index fast full scans (direct read)
0
SQL>
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Mladen Gogala
http://mgogala.freehostia.com