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Oracle® Database Reference
11g Release 2 (11.2)

E40402-14
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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