On Sat, Sep 03, 2022 at 10:06:58AM +0900, Michael Paquier wrote: > Ohoh. This sounds like a good idea to me, close to what John has > applied lately. I'll take a closer look..
So, the two code paths patched here are rather isolated. The one in TransactionIdIsInProgress() requires an overflowed set of subxids still running, something similar to what the isolation test subxid-overflow does. XidIsConcurrent() is also kind of hard to reason about with a benchmark. Anyway, I did not know about the work done with SIMD instructions in pg_lfind.h and after playing the API I have run some micro benchmarks with on pg_lfind32() and I can see some improvements. With a range of 100~10k elements in a fixed number of repeated calls with a for loop and lfind(), I could not get up to the 40% speedup. That was somewhat closer to 15%~20% on x86 and 20%~25% with arm64. There is a trend where things got better with a higher number of elements with lfind(). In short, switching those code paths to use the linear search routines looks like a good thing in the long-term, so I would like to apply this patch. If you have any comments or objections, please feel free. -- Michael
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