core: reduce allocs in hot method: priceHeap.Less() #31
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I did some cpu profiling with pprof during a benchmark execution. Here is
top
:The
priceHeap.Less
method looked suspicious. It turns out it just compares two transactions' gas prices:h[i].GasPrice().Cmp(h[j].GasPrice())
. Digging deeper,Transaction.GasPrice
(reasonably) returns a copy of abig.Int
, rather than its own (mutable) field value.Less
is only inspecting, so we'd prefer direct access to the field. The newTransaction.CompareGasPrice
method compares the unexported fields directly, reducing allocations from copying and heap garbage.BenchmarkTransaction_CompareGasPrice
illustrates the difference:This is a cpu profile after making the change:
Notably,
CompareGasPrice
is lower thanLess
was, andruntime.mallocgc
dropped.I assume that
runtime.cgocall
is leveldb, which we'd rather not mess with if we don't have to.