1. Check for the version of previous Postgresql installation.
/.../data/PG_VERSION (location of directory data under previous postgresql installation directory)
2. Check if it matches the current version i.e if the version of Postgresql from PG_VERSION file matches your current Postgresql installation
- >If the versions match, just clean start your postgresql using your old directory in the data path
pg_ctl start -D /data path to previous installation/
or alternatively you can use
postmaster -D /data path to previous installation/- > if the versions don't match as it was in my case, [I had Postgresql 7.4 installed previously and now I wanted to get the data on to Postgresql 8.4] we have to do a bit more than just starting database server with old data path.
Steps to recover data from previous version of Postgresql
a) install Postgresql 7.4 (remember even if you cannot find version 7.4 you can install any 7.x version)
for this, I downloaded the source and compiled and installed it on my system
Ubuntu users don't have to go through all this they can directly use binary package download from
https://launchpad.net/ubuntu/+source/postgresql/7.4.5-3
This site also has downloadable source code so people who use Linux flavors for which binary is not available can rebuild the binary on their system locally.
RPM binary packages are also available from www.postgresql.org
http://www.postgresql.org/ftp/binary/v7.4.17/
Once installed, use the command in step-2, Postgresql should mount the database without any errors, login to postgresql database server and you should be able to see all your previous data.
