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What should be done about non-atomicity of Table.counter_set() #1549
Description
See #1541 for discussion.
There is a note from the HappyBase source code
Note that application code should never store a incremented or decremented counter value directly; use the atomic
Table.counter_incandTable.counter_decmethods for that.
and we just went one step further and just made Table.counter_set() a not implemented method (it raises NotImplementedError when called).
Activity
tseaver commentedon Mar 8, 2016
Similar to #1524?
dhermes commentedon Mar 9, 2016
Nope. This is an issue of a single request not being transactional while that one is the issue of having to send
N + 1requests at once to match an HBase / Thrift feature.tseaver commentedon Jul 1, 2016
@dhermes Could we map
happybase.table.Table.counter_setonto aCheckAndMutateRowrequest, where the predicate checked that there was no value alraeady set? We would leavefalse_mutationsempty in that case.dhermes commentedon Jul 2, 2016
We should verify that that would actually be atomic though. I'd guess the "check" and "mutate" don't actually happen atomically (would be a high cost to pay for every
CheckAndMutateRowmade).tseaver commentedon Jul 19, 2016
The docs for the
Bigtabledata interface say:dhermes commentedon Jul 19, 2016
@tseaver It could mean that the set of mutations are either all applied or none, not implying anything about the atomicity of the "check and mutate" as a single operation.
@mbrukman @tswast can you weigh in?
mbrukman commentedon Jul 19, 2016
It's unclear to me how
Table.counter_set()would map to aCheckAndMutate—it only accepts a row, column, and value, but not the previous value, so there's nothing to check against, unless I'm missing something. What would we check against as the previous value?The use case that it presumably addresses is to enable a user to reset a counter to 0, or initialize the state from some non-zero value if they're migrating data from elsewhere and want to start from a known state, rather than increment their way up to it.
tseaver commentedon Jul 19, 2016
From #1989 just now: @garye wrote:
garye commentedon Jul 19, 2016
I took it back over on #1989, see if you think that makes sense.
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