On Mon, Apr 1, 2019 at 10:17 AM Christoph Berg <m...@debian.org> wrote:
> Re: Tomas Vondra 2019-03-30 <20190330192543.GH4719@development> > > I have not investigated the exact reasons, but my hypothesis it's about > > the amount of WAL generated during the initial CREATE INDEX (because it > > probably ends up setting the hint bits), which puts additional pressure > > on the storage. > > > > Unfortunately, this additional cost is unlikely to go away :-( > > If WAL volume is a problem, would wal_compression help? > > > Now, maybe we want to enable checksums by default anyway, but we should > > not pretent the only cost related to checksums is CPU usage. > > Thanks for doing these tests. The point I'm trying to make is, why do > we run without data checksums by default? For example, we do checksum > the WAL all the time, and there's not even an option to disable it, > even if that might make things faster. Why don't we enable data > checksums by default as well? > I think one of the often overlooked original reasons was that we need to log hint bits, same as when wal_log_hints is set. Of course, if we consider it today, you have to do that in order to use pg_rewind as well, so a lot of people who want to run any form of HA setup will be having that turned on anyway. I think that has turned out to be a much weaker reason than it originally was thought to be. -- Magnus Hagander Me: https://www.hagander.net/ <http://www.hagander.net/> Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>
