On 22/08/2018 08:20, Noah Misch wrote:
> Regardless of the choice of jit={on|off} default, these numbers tell me that
> some or all of jit_*_cost defaults are too low.That was also my earlier analysis. I'm suspicious that we haven't had much feedback about this. We've heard of one or two cases where LLVM broke a query outright, and that was fixed and that was a good result. But we haven't heard anything about performance regressions. Surely there must be some. There hasn't been any discussion or further analysis of the default cost settings either. I feel that we don't have enough information. Another problem is that LLVM is only enabled in some versions of packages. For example, in the PGDG RPMs, it's enabled for RHEL 7 but not RHEL 6. So you could be in for a surprise if you upgrade your operating system at some point. I would like, however, that we make a decision one way or the other before the next beta. I've been handwaving a bit to users not to rely on the current betas for performance testing because the defaults might change later. That's bad either way. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
