Re: Experimental patch for inter-page delay in VACUUM

Bruce Momjian wrote:

> Jan Wieck wrote:
>> Bruce Momjian wrote:
>>
>> > Jan Wieck wrote:
>> >> Bruce Momjian wrote:
>> >>
>> >> > Now, O_SYNC is going to force every write to the disk. If we have a
>> >> > transaction that has to write lots of buffers (has to write them to
>> >> > reuse the shared buffer)
>> >>
>> >> So make the background writer/checkpointer keeping the LRU head clean. I
>> >> explained that 3 times now.
>> >
>> > If the background cleaner has to not just write() but write/fsync or
>> > write/O_SYNC, it isn't going to be able to clean them fast enough. It
>> > creates a bottleneck where we didn't have one before.
>> >
>> > We are trying to eliminate an I/O storm during checkpoint, but the
>> > solutions seem to be making the non-checkpoint times slower.
>> >
>>
>> It looks as if you're assuming that I am making the backends unable to
>> write on their own, so that they have to wait on the checkpointer. I
>> never said that.
>
> Maybe I missed it but are those backend now doing write or write/fsync?
> If the former, that is fine. If the later, it does seem slower than it
> used to be.

In my all_performance.v4.diff they do write and the checkpointer does
write+sync.

Jan

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