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.
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Instance from which the blocks are transferred |
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Class of the cache block |
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The number of blocks that were sent by a particular instance but that never arrived in this instance |
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The time waited for blocks that were sent by a particular instance but that never arrived in this instance |
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CR Block transfers not affected by remote processing delays |
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Total time waited for CR blocks from a particular instance (includes the other times) |
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The count of CR blocks which were received by this instance from a particular instance after a 2-way round-trip |
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The time waited for CR blocks which were received by this instance from a particular instance after a 2-way round-trip |
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The count of CR blocks which were received by this instance from a particular instance after a 3-way round-trip |
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The time waited for CR blocks which were received by this instance from a particular instance after a 3-way round-trip |
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CR Block transfers affected by remote contention |
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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 |
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CR Block transfers affected by remote system load |
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The time waited for CR blocks which were received by this instance from a particular instance and which were delayed because LMS was busy |
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Current block transfers not affected by remote processing delays |
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Total time waited for current blocks from a particular instance (includes the other times |
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The count of current blocks which were received by this instance from a particular instance after a 2-way round-trip |
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The time waited for current blocks which were received by this instance from a particular instance after a 2-way round-trip |
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The count of current blocks which were received by this instance from a particular instance after a 3-way round-trip |
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The time waited for current blocks which were received by this instance from a particular instance after a 3-way round-trip |
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Current block transfers affected by remote contention |
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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 |
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Current block transfers affected by remote system load |
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The time waited for current blocks which were received by this instance from a particular instance and which were delayed because LMS was busy |
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The ID of the container to which the data pertains. Possible values include:
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