On 24/10/13 12:24, Peter Geoghegan wrote:
> On Wed, Oct 23, 2013 at 4:14 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
>> The last bucket would be limited to 8ms < x <= 16 ms. If you find something
>>> 16ms, then you have to rescale *before* you increment any of the buckets.
>> Once you do, there is now room to hold it.
> How is that laid out in shared memory? If the answer is an array of 32
> int64s, one per bucket, -1 from me to this proposal. A huge advantage
> of pg_stat_statements today is that the overhead is actually fairly
> modest. I really want to preserve that property.
>
32 int64 buckets is only 256 bytes, so a thousand histograms would be
less than a quarter of a MB. Any machine that busy, would likely have
many GB's of RAM. I have 32 GB on my development machine.
Though, I suppose that the option to have such histograms could be off
by default, which would seem reasonable. How about a convention not to
have histgrams, when the parameter specifying the width of the first
bucket was either missing or set to zero (assuming a 'negative value'
would be a syntax error!).
Cheers,
Gavin
