Use LVM Snapshots to rollback Postgresq

psql_snap.sh

#!/bin/bash
# This was to create a quick snapshot of the database, make the changes I
# wanted, and then revert the database to exactly the way it was before I
# snapshotted it.

LV=pg_ot
VG=$(/sbin/vgdisplay -s | sed -e 's/  "\([^"]*\)" .*/\1/')
MTPT=/var/lib/postgresql/11/main
PROC=postgres
VERSION=11
SIZE=100G

LVM_DEV="/dev/$VG/$LV"
LVM_SNAP="$LVM_DEV-snap"

if [ "$(whoami)" != "root" ]; then
    echo "Run as root!"
    exit 1
fi
un_mount () {
    mount | grep "$MTPT" | cut -d' ' -f 3 | sort -r | while read dir; do
        while findmnt "$dir" > /dev/null; do
            echo "found $dir to unmount"
            umount "$dir" || { echo "relevant processes: "; lsof +D "$dir" 2>/dev/null; }
            /sbin/fsck -fy "$LVM_DEV"
            sleep 2
        done
    done
}

start_snapshot() {
    un_mount
    lvcreate --snapshot --size $SIZE --name $LV-snap "$LVM_DEV"
    mount "$LVM_SNAP" "$MTPT" 2>/dev/null
}
stop_snapshot() {
    un_mount
    /sbin/lvremove --force "$LVM_SNAP"
    mount "$LVM_DEV" "$MTPT" 2>/dev/null
}

startproc() {
    pg_ctlcluster $VERSION main start
    /etc/init.d/pgpool2 restart
}
stopproc() {
    /etc/init.d/pgpool2 stop
    pg_ctlcluster $VERSION main stop
    sleep 2
}

case $1 in
    start)
        if [ -b "$LVM_SNAP" ]; then
            echo "Already set up"
            exit 1
        fi
        stopproc
        start_snapshot
        systemctl start postgresql
        startproc
        ;;
    stop)
        if ! [ -b "$LVM_SNAP" ]; then
            echo "None Exists"
            exit 1
        fi
        stopproc
        stop_snapshot
        startproc
        ;;
    restart)
        stopproc
        stop_snapshot
        start_snapshot
        startproc
        ;;
    *)
        echo "start|stop|restart";
        ;;
esac;