Hi, On 2019-05-07 16:14:43 +0000, Steven Winfield wrote: > (Apologies if this isn't the right place to post this) Seems right. > A few days ago a blog post appeared on phoronix.com[1] comparing GCC 8.3.0 against 9.0.1 on Intel cascadelake processors. > A notable difference was seen in the PostgreSQL benchmark (v10.3, pgbench, read/write, more detail below), both when compiling with -march=native and -march=skylake: > > GCC version | -march= | TPS > 8.3.0 | skylake | 5667 > 9.0.1 | skylake | 11684 (2.06x speed up) > 8.3.0 | native | 8075 > 9.0.1 | native | 11274 (1.40x speed up) > > I'm interested to know the devs' take on this is - does GCC 9 contain some new feature(s) that are particularly well suited to compiling and optimising Postgres? Or was GCC 8 particularly bad? I think those numbers are just plain bogus. read/write pgbench is commonly IO bound. My suspicion is much more that the tests for gcc 8 and 9 were executed in the same postgres cluster (in which case the second will be faster, because it'll have pre-initialized WAL files). Or something of that vein. > (after patching it so that it can run as root) That, uh, seems odd. > - pgbench -i -s <system memory in MB * 0.003> pgbench That's pretty small, but whatever. Here's my results: I ran: pgbench -i -q -s 96 && pgbench -n -c 8 -j 8 -T 100 -P1 gcc 8.3, march=native (on skylake): first run: tps = 14436.465265 (excluding connections establishing) second run: tps = 13293.266789 (excluding connections establishing) third run after postgres restart (and thus a checkpoint): tps = 14270.248273 (excluding connections establishing) gcc 9.1, march=native (on skylake): first run: tps = 13836.231981 (excluding connections establishing) second run: tps = 13304.975550 (excluding connections establishing) third run after postgres restart (and thus a checkpoint): tps = 14390.246324 (excluding connections establishing) As you can see the test results are somewhat unstable - the test duration of 60s is just not long enough. But there's no meaningful evidence of a large speedup here. > This email is confidential. If you are not the intended recipient, please advise us immediately and delete this message. > The registered name of Cantab- part of GAM Systematic is Cantab Capital Partners LLP. > See - http://www.gam.com/en/Legal/Email+disclosures+EU for further information on confidentiality, the risks of non-secure electronic communication, and certain disclosures which we are required to make in accordance with applicable legislation and regulations. > If you cannot access this link, please notify us by reply message and we will send the contents to you. > > GAM Holding AG and its subsidiaries (Cantab – GAM Systematic) will collect and use information about you in the course of your interactions with us. > Full details about the data types we collect and what we use this for and your related rights is set out in our online privacy policy at https://www.gam.com/en/legal/privacy-policy. > Please familiarise yourself with this policy and check it from time to time for updates as it supplements this notice. This is a public list. Greetings, Andres Freund
