Hello, On Thu, Mar 16, 2023 at 10:30 AM Yuya Watari <watari.y...@gmail.com> wrote: > My idea is to compute the bitwise OR of all bitmapwords of the result > Bitmapset. The bitwise OR can be represented as a single operation in > the machine code and does not require any conditional branches. If the > bitwise ORed value is zero, we can conclude the result Bitmapset is > empty. The costs related to this operation can be almost negligible; > it is significantly cheaper than calling bms_is_empty_internal() and > less expensive than using a conditional branch such as 'if.'
After posting the patch, I noticed that my patch had some bugs. My idea above is not applicable to bms_del_member(), and I missed some additional operations required in bms_del_members(). I have attached the fixed version to this email. I really apologize for making the mistakes. Should we add new regression tests to prevent this kind of bug? The following tables illustrate the result of a re-run experiment. The significant improvement was a mistake, but a speedup of about 2% was still obtained when the number of partitions, namely n, was large. This result indicates that the optimization regarding bms_is_empty_internal() is effective on some workloads. Table 1: Planning time (ms) (n: the number of partitions of each table) ----------------------------------------------------------------- n | Master | Patched (trailing-zero) | Patched (bitwise-OR) ----------------------------------------------------------------- 1 | 36.903 | 36.621 | 36.731 2 | 35.842 | 35.031 | 35.704 4 | 37.756 | 37.457 | 37.409 8 | 42.069 | 42.578 | 42.322 16 | 53.670 | 67.792 | 53.618 32 | 88.412 | 100.605 | 89.147 64 | 229.734 | 271.259 | 225.971 128 | 889.367 | 1272.270 | 870.472 256 | 4209.312 | 8223.623 | 4129.594 ----------------------------------------------------------------- Table 2: Planning time speedup (higher is better) ------------------------------------------------------ n | Patched (trailing-zero) | Patched (bitwise-OR) ------------------------------------------------------ 1 | 100.8% | 100.5% 2 | 102.3% | 100.4% 4 | 100.8% | 100.9% 8 | 98.8% | 99.4% 16 | 79.2% | 100.1% 32 | 87.9% | 99.2% 64 | 84.7% | 101.7% 128 | 69.9% | 102.2% 256 | 51.2% | 101.9% ------------------------------------------------------ -- Best regards, Yuya Watari
v2-0001-Remove-bms_is_empty_internal-function-calls.patch
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