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 |