Date: Wed, 20 Dec 2023 12:50:31 +0100
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: "Dischner, Anton" <Anton.Dischner@med.uni-muenchen.de>
Cc: Rajesh Kumar <rajeshkumar.dba09@gmail.com>,
	Pgsql-admin <pgsql-admin@lists.postgresql.org>
Subject: Re: AW: Truncate data from whole cluster
Message-ID: <ZYLVBxk3PJ2KHDZy@depesz.com>
Reply-To: depesz@depesz.com
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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