Hi Maria,
It dawn on me we can look at the storage estimate spreadsheet =)
Based on the spreadsheet, we will have 15 billion entries in
DIASource table after DR1, that is ~84 K new rows per visit.
I think we should go with this number (and follow the future
spreadsheet updates)
thanks
Jacek
- you assume we will need to read DIASource row size (300 bytes) x
number of DIASources (10 million): is that sufficient given that 1
DIASource represents one measurement in one filter? (I don't know,
will check with Tim and others at "prototype platform" meeting next
week)
- "M = something like the number of times (epochs) that an object has
been detected by Difference Image processing? [I really have no idea
what is this number is]".
By the time we reach DR1, each field will be observed ~60 times. Also,
recall that only ~10% of all measurements will have high
signal-to-noise. I am not too sure whether your assessment "assuming M
= 1 DIA source per object" is correct, my feeling is it will be more
than 1 (again, I will try to check)
The problem I have trying to figure out this number M is .. I don't fully
understand what is the content of the DIA Source table.
As I understand it:
Using Difference Image Processing helps you to detect those things that change.
So my presumption is that the DIA source table contains different epochs for
one object, but mainly only for variable objects. We have 5% of variable
objects in one FOV in the worst case but we cannot detect all of them becouse
as you say we will be detecting only high signal to noise because in a single
exposure you cannot go very deep.
However as I recall from the meeting, during (or after) deep processing we were
going to store more DIA sources which I assume corresponds to those thing you
could not detect in a single exposure.
Any way, so in the worst case lets assume I can detect all existing variable
objects in the Galactic Plane => 5% of 10 000 000 = 500 000
M = 500 000 * 60 epochs = 3 000 000 (+ flashes, moving objetcs ~ tiny)
So my 1 DIA source per object is a very overshooting but if the DIA source
tables contains information about No Variable objects then the 1 DIA source per
object can be very underestimated.
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