Bruce Momjian <pgman@candle.pha.pa.us> writes:
>> O_DIRECT is only being used for WAL page writes (or I sure hope so
>> anyway), so shared_buffers should be irrelevant.
> Uh, O_DIRECT really just enables when open_sync is used, and I assume
> that is not used for writing dirty buffers during a checkpoint.
I double-checked that O_DIRECT is really just used for WAL, and only
when the sync mode is open_sync or open_datasync. So it seems
impossible that it affected a run with mode fdatasync. What seems the
best theory at the moment is that the grouped-WAL-write part of the
patch doesn't work so well as we thought.
regards, tom lane