* Petr Jelinek (petr.jeli...@2ndquadrant.com) wrote: > On 21/01/17 17:31, Stephen Frost wrote: > > This is just changing the *default*, not requiring checksums to always > > be enabled. We do not hold the same standards for our defaults as we do > > for always-enabled code, for clear reasons- not every situation is the > > same and that's why we have defaults that people can change. > > I can buy that. If it's possible to turn checksums off without > recreating data directory then I think it would be okay to have default on.
I'm glad to hear that. > >> The change of wal_level was supported by benchmark, I think it's > >> reasonable to ask for this to be as well. > > > > No, it wasn't, it was that people felt the cases where changing > > wal_level would seriously hurt performance didn't out-weigh the value of > > making the change to the default. > > Really? Yes. > https://www.postgresql.org/message-id/d34ce5b5-131f-66ce-f7c5-eb406dbe0...@2ndquadrant.com From the above link: > So while it'd be trivial to construct workloads demonstrating the > optimizations in wal_level=minimal (e.g. initial loads doing CREATE > TABLE + COPY + CREATE INDEX in a single transaction), but that would be > mostly irrelevant I guess. > Instead, I've decided to run regular pgbench TPC-B-like workload on a > bunch of different scales, and measure throughput + some xlog stats with > each of the three wal_level options. In other words, there was no performance testing of the cases where wal_level=minimal (the old default) optimizations would have been compared against wal_level > minimal. I'm quite sure that the performance numbers for the CREATE TABLE + COPY case with wal_level=minimal would have been *far* better than for wal_level > minimal. That case was entirely punted on as "mostly irrelevant" even though there are known production environments where those optimizations make a huge difference. Those are OLAP cases though, and not nearly enough folks around here seem to care one bit about them, which I continue to be disappointed by. Even so, I *did* agree with the change to the default of wal_level, based on an understanding of its value and that users could change to wal_level=minimal if they wished to, just as I am arguing that same thing here when it comes to checksums. Thanks! Stephen
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