[Pytables-users] details of user's guide performance plots

[damon f. <dam...@ya...>]

Hi,

I wonder if someone can shed a little light on Figures
6.1 and 6.2 in the User's Guide.  The horizontal axis
is labeled "Number of rows".  I assume from the scale
on that axis that this is "Number of rows in table"
and not "Number of rows accessed".  That isn't stated
directly anywhere in the text, though it is suggested
by the wording of the 4th paragraph in section 6.2.2. 
(I assume a 900MHz machine could not access 6e+08 rows
in a second...)

If the axis is actually "Number of rows in table",
does anyone know roughly how many rows were accessed
for each data point?  Is the number of rows accessed
the same for all data points or does the number of
rows satisfying "table.where(table.cols.var1 <= 20)"
grow with table size?  If it grows with table size, is
it linear?

Finally, for the table being accessed, are the rows
ordered by "var1", in which case there is no disk
seeking going on, or are rows with various values of
"var1" scattered throughout the table, in which case
the index is accessed seqentially, but the data would
be more or less randomly accessed, i.e. would require
disk seeks.

I can only make sense of the figures if I first assume
that the horizontal axis should read "Number of rows
in table".  If this is correct (or even if it is not
correct) perhaps it could be clarified in the text
and/or axis label.

Given that, I have to make one further assumption to
understand the figures, but in this case I'm not sure
what is correct.  I can either assume that a large
number of rows is accessed, that this number grows
linearly with table size and that rows in the table
appear in order of variable "var1".  Or, I can assume
that a small number or rows is accessed, that this
number may grow (probably sublinearly) with table
size, and that rows with a given value of var1 are
scattered throughout the table.  Which of these
assumptions, if either, is correct?


Thanks!
  Damon


		
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