#!/bin/bash
# Reproduces every claim in https://www.heatware.net/postgresql/reload-config-with-pg-ctl/
#
# Creates a throwaway PostgreSQL cluster in a temp directory on port 55432,
# runs each demonstration, prints the output, and removes the cluster.
# It does not touch any existing PostgreSQL installation or data.
#
# Requires: initdb, pg_ctl, psql on PATH (any PostgreSQL 12+).
# Usage: bash verify-postgresql-reload-config.sh

set -u
PORT=55432
PGDATA_TMP="$(mktemp -d -t hwverify)"
trap 'pg_ctl -D "$PGDATA_TMP" stop -m immediate >/dev/null 2>&1; rm -rf "$PGDATA_TMP"' EXIT

hr(){ printf '\n\033[1m%s\033[0m\n' "$*"; }
q(){ psql -h 127.0.0.1 -p $PORT -U postgres -X "$@"; }

command -v initdb >/dev/null || { echo "initdb not on PATH"; exit 1; }

hr "Environment"
initdb --version
psql --version

hr "Creating a throwaway cluster in $PGDATA_TMP"
initdb -D "$PGDATA_TMP" -U postgres --auth=trust >/dev/null 2>&1 || { echo "initdb failed"; exit 1; }
pg_ctl -D "$PGDATA_TMP" -o "-p $PORT" -l "$PGDATA_TMP/server.log" start >/dev/null 2>&1
sleep 2
q -At -c "SELECT version();"

hr "CLAIM 1: 'pg_ctl reload' with no -D and no PGDATA fails"
( unset PGDATA; pg_ctl reload )
echo "exit code: $?  <-- expect 1"

hr "CLAIM 2: 'pg_ctl -D <datadir> reload' succeeds"
pg_ctl -D "$PGDATA_TMP" reload
echo "exit code: $?  <-- expect 0"

hr "CLAIM 3: SELECT pg_reload_conf() returns t"
q -At -c "SELECT pg_reload_conf();"

hr "CLAIM 4: a sighup-context setting (work_mem) DOES apply on reload"
echo -n "before: "; q -At -c "SHOW work_mem;"
echo "work_mem = '8MB'" >> "$PGDATA_TMP/postgresql.conf"
pg_ctl -D "$PGDATA_TMP" reload >/dev/null 2>&1; sleep 1
echo -n "after:  "; q -At -c "SHOW work_mem;"
echo "        ^ expect 4MB -> 8MB"

hr "CLAIM 5: a postmaster-context setting (shared_buffers) does NOT apply on reload"
echo -n "before: "; q -At -c "SHOW shared_buffers;"
echo "shared_buffers = '256MB'" >> "$PGDATA_TMP/postgresql.conf"
pg_ctl -D "$PGDATA_TMP" reload >/dev/null 2>&1; sleep 1
echo -n "after:  "; q -At -c "SHOW shared_buffers;"
echo "        ^ expect NO change, and no error anywhere"

hr "CLAIM 6: pg_settings.pending_restart is how you find out"
q -c "SELECT name, setting, pending_restart FROM pg_settings WHERE pending_restart;"

hr "CLAIM 7: the reload is visible in the server log"
grep -c "received SIGHUP" "$PGDATA_TMP/server.log" | sed 's/^/SIGHUP entries in log: /'

hr "How many settings require a restart on this version?"
q -At -c "SELECT count(*) FROM pg_settings WHERE context='postmaster';"

hr "Done — cluster removed"