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The v$cache_transfer and v$file_cache_transferviews are used to examine Real Application Clusters statistics.
The types of blocks that use the cluster interconnects in a RAC environment
are monitored with the v$ cache
transfer series of views:
·
v$cache_transfer -- This view shows the types
and classes of blocks that Oracle transfers over the cluster interconnect
on a per-object basis. You would use the FORCED_READS and
FORCED_WRITES columns to determine the types of objects your RAC
instances are sharing. Values in the FORCED_WRITES column provide
counts of how often a certain block type experiences a transfer out of a
local buffer cache because the current version was requested by another
instance. These columns are the same for all of the views.
·
v$class_cache_transfer
-- Use this view to identify the class of blocks that experience cache
transfers. v$class_cache_transfer has a CLASS column showing
the class of a block. Therefore, use this view to assess block transfers per
class of object.
·
v$file_cache_transfer -- Use this view to
monitor the blocks transferred per file. The FILE_NUMBER column identifies
the datafile that contained the blocks transferred.
·
v$temp_cache_transfer
-- Use this view to monitor the transfer of temporary tablespace blocks. The
view contains a FILE_NUMBER column that is used to track, by the tempfile
file number, the number of blocks transferred. This view has the same
structure as the v$temp_cache_transfer view.
The contents of the v$cache_transfer
view are shown below.
Description of the V$CACHE_TRANSFER view
Name Type
----------------------- --------------
FILE# NUMBER
BLOCK# NUMBER
CLASS# NUMBER
STATUS VARCHAR2(5)
XNC NUMBER
FORCED_READS NUMBER
FORCED_WRITES NUMBER
NAME VARCHAR2(30)
PARTITION_NAME VARCHAR2(30)
KIND VARCHAR2(15)
OWNER# NUMBER
GC_ELEMENT_ADDR RAW(4)
GC_ELEMENT_NAME NUMBER
The v$cache_transfer view shows the
types and classes of blocks that Oracle transfers over the cluster
interconnect on a per-object basis. The FORCED_READS
and FORCED_WRITES columns are used to determine which
types of objects the RAC instances are sharing.
Values in the FORCED_WRITES column provide counts of how often a certain
block type experiences a transfer out of a local buffer cache because the
current version was requested by another instance. Use the
v$file_cache_transfer view to identify
files that experience cache transfers. For example, while
v$cache_transfer has a NAME column
showing the name of an object, the
v$file_cache_transfer view has the FILE_NUMBER column to show the
file numbers of the datafiles that are the source of blocks transferred.
Therefore, use this view to assess block transfers per file. The
v$file_cache_transfer view contents are
shown below.
Description of the V$FILE_CACHE_TRANSFER View
Name Type
-------------------------------- ----------
FILE_NUMBER NUMBER
X_2_NULL NUMBER
X_2_NULL_FORCED_WRITE NUMBER
X_2_NULL_FORCED_STALE NUMBER
X_2_S NUMBER
X_2_S_FORCED_WRITE NUMBER
S_2_NULL NUMBER
S_2_NULL_FORCED_STALE NUMBER
RBR NUMBER
RBR_FORCED_WRITE NUMBER
RBR_FORCED_STALE NUMBER
NULL_2_X NUMBER
S_2_X NUMBER
NULL_2_S NUMBER
CR_TRANSFERS NUMBER
CUR_TRANSFERS NUMBER
Even though the shared disk architecture virtually eliminates forced disk
writes, the v$cache_transfer and
v$file_cache_transfer views may still
show the number of block mode conversions per block class or object.
However, values in the FORCED_WRITES column will be zero.
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