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st: Questions on the performance of the -expand- command


From   Sergiy Radyakin <serjradyakin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Questions on the performance of the -expand- command
Date   Tue, 26 Oct 2010 12:59:12 -0400

Hi, All!

Since expand is a built-in command, this might probably be relevant
only to the developers of Stata.

1) Can somebody advise if there is anything fundamental that prevents
-expand- to fail immediately when there is not enough memory?

Below is an example where it takes 55 seconds to realize that there is
not enough memory, however it seems that the exact memory
requirement can be computed beforehand and checked. An opposite case
might be -reshape- where it is not immediately clear how much
memory will be required.

2) The multiprocessor performance report does not list the performance
of the -expand- command (or I couldn't find it??). It seems to be
perfectly parallelizable both from the theoretical point of view and
from actual observations, but can somebody please confirm this? Are
there other commands that are missing from the MP-report?

Thank you, Sergiy Radyakin





. set mem 6g

Current memory allocation

                    current                                 memory usage
    settable          value     description                 (1M = 1024k)
    --------------------------------------------------------------------
    set maxvar         5000     max. variables allowed           1.947M
    set memory         6144M    max. data space              6,144.000M
    set matsize         400     max. RHS vars in models          1.254M
                                                            -----------
                                                             6,147.201M
r; t=0.08 12:37:56

. sysuse auto
(1978 Automobile Data)
r; t=0.00 12:38:00

. expand 10000000
no room to add more observations
    An attempt was made to increase the number of observations beyond
what is currently possible.  You have the following alternatives:

     1.  Store your variables more efficiently; see help compress.
(Think of Stata's data area as the area of a rectangle; Stata can
trade off width and
         length.)

     2.  Drop some variables or observations; see help drop.

     3.  Increase the amount of memory allocated to the data area
using the set memory command; see help memory.
r(901); t=55.07 12:39:08
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