Обсуждение: Truncate data from whole cluster

On Wed, Dec 20, 2023 at 02:35:52PM +0530, Rajesh Kumar wrote:
> Hi all,
> 
> I am using postgres 15.2. one leader and one replica. I have multiple dbs
> and multiple tables. I want to keep definitions and only want to delete
> 'data only' from all dbs and tables.
> 
> Any command to do that instead of truncating all tables one by one?

No such command exists. For starters, no command in SQL can do stuff in
other databases than the one you are connected to.

You can write a simple one-liner that will do it, in your shell.
shouldn't be really complex - get list of dbs, and in each db connect
with psql and truncate all tables. basically: `psql | xargs psql`

depesz

Hi all,

if you ask Bard LLM do do this you get:

#!/bin/bash

# List all databases in the PostgreSQL instance databases=$(psql -t -c "SELECT datname FROM pg_database;")

# Truncate table data for each database
for database in $databases; do
  echo "Processing database '$database'..."
  psql -d $database -c "SET FOREIGN_KEY_CHECKS=0;"
  tables=$(psql -d $database -t -c "SELECT tablename FROM pg_catalog.pg_tables WHERE schemaname = 'public';")
  for table in $tables; do
    echo "Truncating table '$table' in database '$database'..."
    psql -d $database -c "TRUNCATE TABLE $table;"
  done
  psql -d $database -c "SET FOREIGN_KEY_CHECKS=1;"
done

This may be a good script to start.
You will definetly test this first on a test installation!

Best,

Anton

-----Ursprüngliche Nachricht-----
Von: depesz@depesz.com <depesz@depesz.com> 
Gesendet: Mittwoch, 20. Dezember 2023 11:24
An: Rajesh Kumar <rajeshkumar.dba09@gmail.com>
Cc: Pgsql-admin <pgsql-admin@lists.postgresql.org>
Betreff: Re: Truncate data from whole cluster

On Wed, Dec 20, 2023 at 02:35:52PM +0530, Rajesh Kumar wrote:
> Hi all,
> 
> I am using postgres 15.2. one leader and one replica. I have multiple 
> dbs and multiple tables. I want to keep definitions and only want to 
> delete 'data only' from all dbs and tables.
> 
> Any command to do that instead of truncating all tables one by one?

No such command exists. For starters, no command in SQL can do stuff in other databases than the one you are connected
to.

You can write a simple one-liner that will do it, in your shell.
shouldn't be really complex - get list of dbs, and in each db connect with psql and truncate all tables. basically:
`psql| xargs psql`
 

depesz

On Wed, Dec 20, 2023 at 11:39:40AM +0000, Dischner, Anton wrote:
> Hi all,
> 
> if you ask Bard LLM do do this you get:
> 
> #!/bin/bash
> 
> # List all databases in the PostgreSQL instance databases=$(psql -t -c "SELECT datname FROM pg_database;")
> 
> # Truncate table data for each database
> for database in $databases; do
>   echo "Processing database '$database'..."
>   psql -d $database -c "SET FOREIGN_KEY_CHECKS=0;"
>   tables=$(psql -d $database -t -c "SELECT tablename FROM pg_catalog.pg_tables WHERE schemaname = 'public';")
>   for table in $tables; do
>     echo "Truncating table '$table' in database '$database'..."
>     psql -d $database -c "TRUNCATE TABLE $table;"
>   done
>   psql -d $database -c "SET FOREIGN_KEY_CHECKS=1;"
> done
> 
> This may be a good script to start.
> You will definetly test this first on a test installation!

No, it's not.
it's full of errors, and hallucinations.

couple of things that took me < 1 minute to notice:

1. will fail for database names that contain spaces in them
2. setting variable like psql -d ... -c "set .." - is pointless, the
   value will be active only for this session, but this session has just
   eneded
3. there is no "FOREIGN_KEY_CHECKS" setting in pg
4. will fail for table names with spaces
5. will ignore tables in non-public schemas
6. will fail for table names with UpperCaseLetters
7. for db with N tables (in public), it will call 101 psql connections
   to this database. if your db has many small tables it will be
   unreasonably slow

depesz, cursing whatever "magic ai tool" people try to use as base for
their scripts