8.9 V$INSTANCE_CACHE_TRANSFER

V$INSTANCE_CACHE_TRANSFER displays statistics for the cache blocks transferred among instances.

Oracle keeps multiple versions of data buffered in the buffer cache. The current buffer (or block), CURRENT_BLOCK, is the most up-to-date copy, containing all recent modifications. A consistent read buffer (or block), CR_BLOCK, contains the version of the data at a particular time prior to the current buffer. It is read-consistent (that is, all the data shown in that buffer are consistent for the start time of a query).

Therefore, for the same data block there can be multiple copies in the buffer cache: one current copy, and one or more consistent read copies with data consistent as of different snapshot times.

Column	Datatype	Description
INSTANCE	NUMBER	Instance from which the blocks are transferred
CLASS	VARCHAR2(18)	Class of the cache block
LOST	NUMBER	The number of blocks that were sent by a particular instance but that never arrived in this instance
LOST_TIME	NUMBER	The time waited for blocks that were sent by a particular instance but that never arrived in this instance
CR_BLOCK	NUMBER	CR Block transfers not affected by remote processing delays
CR_BLOCK_TIME	NUMBER	Total time waited for CR blocks from a particular instance (includes the other times)
CR_2HOP	NUMBER	The count of CR blocks which were received by this instance from a particular instance after a 2-way round-trip
CR_2HOP_TIME	NUMBER	The time waited for CR blocks which were received by this instance from a particular instance after a 2-way round-trip
CR_3HOP	NUMBER	The count of CR blocks which were received by this instance from a particular instance after a 3-way round-trip
CR_3HOP_TIME	NUMBER	The time waited for CR blocks which were received by this instance from a particular instance after a 3-way round-trip
CR_BUSY	NUMBER	CR Block transfers affected by remote contention
CR_BUSY_TIME	NUMBER	The time waited for CR blocks which were received by this instance from a particular instance and which were delayed by a log flushed on the sending instance
CR_CONGESTED	NUMBER	CR Block transfers affected by remote system load
CR_CONGESTED_TIME	NUMBER	The time waited for CR blocks which were received by this instance from a particular instance and which were delayed because LMS was busy
CURRENT_BLOCK	NUMBER	Current block transfers not affected by remote processing delays
CURRENT_BLOCK_TIME	NUMBER	Total time waited for current blocks from a particular instance (includes the other times
CURRENT_2HOP	NUMBER	The count of current blocks which were received by this instance from a particular instance after a 2-way round-trip
CURRENT_2HOP_TIME	NUMBER	The time waited for current blocks which were received by this instance from a particular instance after a 2-way round-trip
CURRENT_3HOP	NUMBER	The count of current blocks which were received by this instance from a particular instance after a 3-way round-trip
CURRENT_3HOP_TIME	NUMBER	The time waited for current blocks which were received by this instance from a particular instance after a 3-way round-trip
CURRENT_BUSY	NUMBER	Current block transfers affected by remote contention
CURRENT_BUSY_TIME	NUMBER	The time waited for current blocks which were received by this instance from a particular instance and which were delayed by a log flushed on the sending instance
CURRENT_CONGESTED	NUMBER	Current block transfers affected by remote system load
CURRENT_CONGESTED_TIME	NUMBER	The time waited for current blocks which were received by this instance from a particular instance and which were delayed because LMS was busy
CON_ID	NUMBER	The ID of the container to which the data pertains. Possible values include: 0: This value is used for rows containing data that pertain to the entire CDB. This value is also used for rows in non-CDBs. 1: This value is used for rows containing data that pertain to only the root n: Where n is the applicable container ID for the rows containing data