Tim,
Thanks. Even after adding detection size = x2 or x3 time dependent db
size, we are still talking about < 20 TB in the first year, more than
factor of 10 smaller than the original top down estimate
Let's talk tomorrow at 11:00
Jacek
Tim Axelrod wrote:
Hi Jacek,
You're certainly right, you do have the right growth properties - my
mistake in reading your spreadsheet.
I have modified the spreadsheet to use what I think is a more reasonable
way of sizing the time-dependent portion. It is keyed to the number
of stars per sq deg to R=24.5, which I am taking to be 10000. This is
an appropriate number for a midlatitude field, and probably not a bad
guess for the all sky average. We can certainly really do the average,
though, since there are nice web accessible star count models. The
average will be quite dependent on the observing strategy we adopt for
LSST, particularly the exclusion region around the galactic plane, if any.
For the moment, I suggest the rough estimate is not too bad. It is
probably reasonable to bump it up by a factor of two to account for the
bright galaxies as well.
The sizing does not yet account for the detection database, as we
discussed previously. This is the one which is affected by the
detection threshold we pick, and the pruning policies we adopt. It
should likely be at least 2x the size of the time dependent db.
Cheers,
Tim
Jacek Becla wrote:
Hi Tim,
Looking at your spreadsheet, I think one problem is that you have the
whole thing growing as a power of 0.56, because you have made the
time-dependent size a fixed fraction of the deep size. Instead, one
grows linearly and the other roughly like the square root. I
haven't yet had the time to completely understand what you've done.
I think the spreadsheet is correct here, there is NO dependency of
time-related data on the 0.56 number, and the time-dependent data
does grow linearly.
>> I think the fraction of variable objects per field is way too high,
>> particularly as the number of objects increases with increasing
>> depth. Most of the deeper objects will be galaxies and the
>> fraction of agn, SN
>> whatever in galaxies is more like .01 than 0.1.
>>
>>
> I agree that this fraction is too high (this one didn't come from me!),
> but it shouldn't affect the size numbers! Any object that has useful
> S/N in a single visit should have entries in the time dependent
> database, whether it is variable or not.
It sounds like I should not be using a simple 0.1 or 0.01 fraction
here, and we need to rewrite the formula. I will need some hints how
to model this.
thanks,
Jacek
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