kv/batcheval: only expose immutable range state to commands #59009
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nvanbenschoten
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The DeclareKeysFunc has always included a full RangeDescriptor, but it has never been clear which fields in this descriptor are safe to use and which are not when declaring keys for a request. The concern is that any property of the RangeDescriptor that is not immutable may change between the time that a request declares its keys to latch and the time that it evaluates, so any assumptions based on these mutable fields may not hold. The quintessential example of a property of a Range that is not immutable is its end key. It would be incorrect to declare keys between a Range's start key and its current end key as a means of latching the entire range, because a merge of a right-hand neighbor could complete in between the time that a request declares its keys and the time that it evaluates. This could lead to a violation of the mutual exclusion that the command was expecting to have. This commit makes these kinds of mistakes impossible to make by putting the RangeDescriptor behind an interface that only exposes the properties of a Range that cannot change across a Range's lifetime.
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tbg
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Jan 19, 2021
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Reviewed 28 of 28 files at r1.
Reviewable status:complete! 0 of 0 LGTMs obtained (waiting on @dt)
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TFTR! bors r+ |
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The DeclareKeysFunc has always included a full RangeDescriptor, but it
has never been clear which fields in this descriptor are safe to use and
which are not when declaring keys for a request. The concern is that any
property of the RangeDescriptor that is not immutable may change between
the time that a request declares its keys to latch and the time that it
evaluates, so any assumptions based on these mutable fields may not
hold.
The quintessential example of a property of a Range that is not
immutable is its end key. It would be incorrect to declare keys between
a Range's start key and its current end key as a means of latching the
entire range, because a merge of a right-hand neighbor could complete in
between the time that a request declares its keys and the time that it
evaluates. This could lead to a violation of the mutual exclusion that
the command was expecting to have.
This commit makes these kinds of mistakes impossible to make by putting
the RangeDescriptor behind an interface that only exposes the properties
of a Range that cannot change across a Range's lifetime.