On 8/3/26 15:36, Hannu Krosing wrote: > For the CPU usage vs compression ratio discussion, please remember > that for both lz4 and zstd this depends on certain "compression > effort" flags, which we do not expose to customers (we claim we > already choose the best ones for them :) ) >
I'm not sure we really make such claims. AFAIK we simply use the default compression levels, specified by the lz4/zstd library, and assume the authors picked the right trade offs. I think that's sensible. > To have a good basis for any recommendation someone could run a bunch > of tests with different compression level flags and compare the > results for CPU usage and compression ration for 8kB pages. > That might be an interesting experiment, but (a) I suspect there'll be a fair amount of dependency on the data set used (e.g. what kind of data is loaded into the DB), and (b) we'd pretty close to release data. I don't think we want to be messing with the compression levels, so for PG19 we're stuck with the current ones. Which means we should pick the default compression algorithm based on that. regards -- Tomas Vondra
