refactor: remove lifetime from DynComparator #542
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This commit removes the need for an explicit lifetime on the `DynComparator`. The rationale behind this change is that callers may wish to share this comparator amongst threads and the explicit lifetime makes this harder to achieve. As a nice side-effect, performance of the sort kernel seems to have improved: ``` $ critcmp master pr group master pr ----- ------ -- bool sort 2^12 1.03 310.8±1.34µs 1.00 302.8±7.78µs bool sort nulls 2^12 1.01 287.4±2.22µs 1.00 284.0±3.23µs sort 2^10 1.04 98.7±3.58µs 1.00 94.6±0.50µs sort 2^12 1.05 510.7±5.56µs 1.00 486.2±9.94µs sort 2^12 limit 10 1.05 48.1±0.38µs 1.00 45.6±0.30µs sort 2^12 limit 100 1.04 52.8±0.37µs 1.00 50.6±0.41µs sort 2^12 limit 1000 1.06 141.1±0.94µs 1.00 132.7±0.95µs sort 2^12 limit 2^12 1.03 501.2±4.01µs 1.00 486.5±4.87µs sort nulls 2^10 1.02 70.9±0.72µs 1.00 69.4±0.51µs sort nulls 2^12 1.02 369.7±3.51µs 1.00 363.0±18.52µs sort nulls 2^12 limit 10 1.01 70.6±1.22µs 1.00 70.0±1.27µs sort nulls 2^12 limit 100 1.00 71.7±0.82µs 1.00 71.8±1.60µs sort nulls 2^12 limit 1000 1.01 80.5±1.55µs 1.00 79.4±1.41µs sort nulls 2^12 limit 2^12 1.05 375.4±4.78µs 1.00 356.1±3.04µs ```
jorgecarleitao
approved these changes
Jul 13, 2021
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Cool. Thanks, @e-dard .
I am not sure why there is this performance improvement, but I agree that cloning the array is cheap and give us the added bonus of Send+Sync of the comparator that some use-cases benefit.
Could you add an issue and link it to this PR (via Closes #issue), so that this shows on the changelog?
Note that this backward incompatible as code using the lifetime qualifier stops compiling.
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I have filed #543 issue for this change |
alamb
approved these changes
Jul 13, 2021
Codecov Report
@@ Coverage Diff @@
## master #542 +/- ##
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+ Coverage 82.54% 82.60% +0.06%
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Files 167 167
Lines 45957 45984 +27
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+ Hits 37934 37985 +51
+ Misses 8023 7999 -24
Continue to review full report at Codecov.
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nevi-me
approved these changes
Jul 14, 2021
alamb
added
api-change
This was referenced Sep 16, 2021
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Which issue does this PR close?
Closes #543
Rationale for this change
The cost of building a comparator (initialising a
DynComparator) is often significantly higher than the actual cost of executing the comparator's closure on two row IDs. Therefore it makes sense to build the comparator once, and re-use the returnedDynComparatorfor each row you are comparing the two arrays on.Due to the explicit lifetime of
DynComparatorI recently found it problematic to store theDynComparatoron an object that was used across threads in an async environment.By refactoring the
build_compareimplementations I was able to remove the lifetime and it's much easier to use in the Datafusion operator I'm improving.As a nice side-effect, the sort kernel benchmarks show an improvement in performance of around 2–5%.
What changes are included in this PR?
I have refactored
DynComparatorto remove the explicit lifetime. I did this by removing the need for theDynComparatorinstantiations to close over references. Instead we just move in owned arrays by cheaply cloning the underlyingArrayData.Further, I took the liberty of making
DynComparatorSend+Sync. Again, this helps when you want to store it on types that need to beSend + Sync.Relative to how often the closure will be called I don't see this as an expensive change.