On Wed, 24 Dec 2025 at 18:08, KAZAR Ayoub <ma_kazar@esi.dz> wrote: > > Hello, > Following the same path of optimizing COPY FROM using SIMD, i found that COPY TO can also benefit from this. > > I attached a small patch that uses SIMD to skip data and advance as far as the first special character is found, then fallback to scalar processing for that character and re-enter the SIMD path again... > There's two ways to do this: > 1) Essentially we do SIMD until we find a special character, then continue scalar path without re-entering SIMD again. > - This gives from 10% to 30% speedups depending on the weight of special characters in the attribute, we don't lose anything here since it advances with SIMD until it can't (using the previous scripts: 1/3, 2/3 specials chars). > > 2) Do SIMD path, then use scalar path when we hit a special character, keep re-entering the SIMD path each time. > - This is equivalent to the COPY FROM story, we'll need to find the same heuristic to use for both COPY FROM/TO to reduce the regressions (same regressions: around from 20% to 30% with 1/3, 2/3 specials chars). > > Something else to note is that the scalar path for COPY TO isn't as heavy as the state machine in COPY FROM. > > So if we find the sweet spot for the heuristic, doing the same for COPY TO will be trivial and always beneficial. > Attached is 0004 which is option 1 (SIMD without re-entering), 0005 is the second one.
Ayoub Kazar, I tested your v4 "copy to" patch, doing everything in RAM, and using the cpupower tips from above. (I wanted to test your v5, but `git apply --check` gave me an error, so I can look at that another day.)
The results look great:
master: (forgot to get commit hash)
text, no special: 8165 text, 1/3 special: 22662 csv, no special: 9619 csv, 1/3 special: 23213
Currently optimizing COPY FROM using SIMD is still under review, but for the case of COPY TO using the same ideas, we found that the problem is trivial, the attached patch gives very nice speedups as confirmed by Manni's benchmarks.
