[GRASS-dev] [GRASS GIS] #2587: copying attribute tables very inefficient if tables are in same database

[GRASS GIS]

#2587: copying attribute tables very inefficient if tables are in same database
--------------------------+------------------------------
  Reporter:  mlennert     |      Owner:  grass-dev@…
      Type:  enhancement  |     Status:  new
  Priority:  normal       |  Milestone:  7.1.0
 Component:  Database     |    Version:  svn-trunk
Resolution:               |   Keywords:  libdb copy table
       CPU:  Unspecified  |   Platform:  Unspecified
--------------------------+------------------------------

Comment (by mlennert):

 To reinforce this:

 I have a vector map with 881,120 points. I have to loop over this map,
 extracting points according to one attribute. When I use v.extract to
 extract the points and to create the table it takes quite a long time,
 most of it in "writing attributes":


 {{{
 time v.extract produnits_light where="cd_nacebel_2010='27120' and
 etab_emploi_onss_2010>0" out=prod_temp --o

 real    0m20.183s
 user    0m12.872s
 sys     0m17.516s
 }}}

 i.e. 20s, although this only extracts 93 points !

 Using a script that extracts the points without attribute table and then
 creates the table using different tools, it is much quicker. Here's the
 script (t.sh):


 {{{
 v.extract -t produnits_light where="cd_nacebel_2010='27120' and
 etab_emploi_onss_2010>0" out=prod_temp --o
 v.db.select produnits_light where="cd_nacebel_2010='27120' and
 etab_emploi_onss_2010>0" sep=, file=test.csv --o
 v.info -c produnits_light --quiet | cut -d'|' -f1 |  sed 's/TEXT/STRING/'
 | sed 's/DOUBLE PRECISION/REAL/' | sed 's/\(.\)\(.*\)/"\1\L\2"/g' | paste
 -s -d ',' > test.csvt
 db.in.ogr input=test.csv out=prod_temp_table --o
 v.db.connect -o prod_temp table=prod_temp_table key=cat_
 }}}


 {{{
 time sh t.sh

 real    0m1.241s
 user    0m1.000s
 sys     0m0.168s
 }}}

 The result is identical except that cat is renamed cat_ by db.in.ogr...

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Ticket URL: <http://trac.osgeo.org/grass/ticket/2587#comment:1>
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