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 roundtrip
`CURRENT_2HOP_TIME`	`NUMBER`	The time waited for current blocks which were received by this instance from a particular instance after a 2-way roundtrip
`CURRENT_3HOP`	`NUMBER`	The count of current blocks which were received by this instance from a particular instance after a 3-way roundtrip
`CURRENT_3HOP_TIME`	`NUMBER`	The time waited for current blocks which were received by this instance from a particular instance after a 3-way roundtrip
`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