Backup complete postgis database with geometry transformation - postgresql

Question

I have a PostGIS enabled PostgreSQL database that is no longer needed in production. I would like to back it up, but the geometry columns of PostGIS should be transformed to a simple, long-term stable text format like WKT.
I'm aware of the ST_AsText function.
SELECT road_id, ST_AsText(road_geom) AS geom, road_name FROM roads;
But how do I apply this to backup the complete database with several tables with geometries and many without?

Answer 1

That's the backup strategy I finally applied:
1. Normal dump of the PostGIS-Postgres database with pg_dump. Plain-text format to improve readability.
2. CSV backup of all tables
For this I created a copy of my initial database ("la_as_text") and transformed all the geometry columns to text with the following script (thanks #Jim Jones). It's very specific for my case, but I decided to post it like this anyway. Just in case somebody runs in the came issues as I did with views that depend on geometry columns and gist indexes. The views won't work if you change the datatype to text and text columns are also not valid for gist indexing.
#!/bin/bash
# has to be run by a user who has owner permissions for the database
rm delete_views.txt delete_views_mod.txt alter_script.txt alter_script_mod.txt
# delete all views - not necessary in long-term-backup and cause problems when altering geometry columns
echo "select 'drop view ' ||table_name|| ';' from information_schema.views where table_schema not in ('pg_catalog', 'information_schema') and table_name "'!'"~ '^pg_';" | psql la_as_text >> delete_views.txt
cat delete_views.txt | tail -n +3 | head -n -2 >> delete_views_mod.txt
cat delete_views_mod.txt | psql la_as_text
# delete one particular gist index that depends on a geometry column -- text can't be indexed with gist
echo "drop index idx_combined_points_the_geom;" | psql la_as_text
# change data type geometry (EWKB) to human readable text (WKT)
echo "select 'alter table '||table_schema||'.'||table_name||' alter column '||column_name||' type text USING ST_AsText('||column_name||');' from information_schema.columns where table_schema = 'public' and udt_name = 'geometry';" | psql la_as_text >> alter_script.txt
cat alter_script.txt | tail -n +3 | head -n -2 >> alter_script_mod.txt
cat alter_script_mod.txt | psql la_as_text
The resulting database lacks a lot of its initial functionality due to the missing geometry data type, but it's human readable.
Instead of a normal dump I exported all the individual tables as ';'-separated text files with the following script:
#!/bin/bash
SCHEMA="public"
DB="la_as_text"
psql -Atc "select tablename from pg_tables where schemaname='$SCHEMA'" $DB |\
while read TBL; do
psql -c "copy $SCHEMA.$TBL to stdout with csv delimiter ';'" $DB > $TBL.csv
done
I'm pretty confident that this backup can be reconstructed in the future -- if necessary.