Re: checkpointer continuous flushing

Hi,

On 2015-06-02 PM 07:19, Fabien COELHO wrote:
>
>> Not that the GUC naming is the most pressing issue here, but do you think
>> "*_flush_on_write" describes what the patch does?
>
> It is currently "*_flush_to_disk". In Andres Freund version the name is
> "sync_on_checkpoint_flush", but I did not found it very clear. Using
> "*_flush_on_write" instead as your suggest, would be fine as well, it
> emphasizes the "when/how" it occurs instead of the final "destination", why
> not...
>
> About words: checkpoint "write"s pages, but this really mean passing the pages
> to the memory manager, which will think about it... "flush" seems to suggest a
> more effective write, but really it may mean the same, the page is just passed
> to the OS. So "write/flush" is really "to OS" and not "to disk". I like the
> data to be on "disk" in the end, and as soon as possible, hence the choice to
> emphasize that point.
>
> Now I would really be okay with anything that people find simple to
> understand, so any opinion is welcome!
>

It seems 'sync' gets closer to what I really wanted 'flush' to mean. If I
understand this and the previous discussion(s) correctly, the patch tries to
alleviate the problems caused by one-big-sync-at-the end-of-writes by doing
the sync in step with writes (which do abide by the
checkpoint_completion_target). Given that impression, it seems *_sync_on_write
may even do the job.

Again, this is a minor issue.

By the way, I tend to agree with others here that there needs to be found a
good balance such that this sync-blocks-one-at-time-in-random-order approach
does not hurt generalized workload too much although it seems to help with
solving the latency problem that you seem set out to solve.

Thanks,
Amit