Much faster bash implementation for rake parallel:prepare (for parallel_tests gem)

parallel_db_setup.sh

#!/bin/bash
set -eo pipefail

DATABASE_NAME="$1"
if [ -z "$PARALLEL_TEST_PROCESSORS" ]; then
  PARALLEL_TEST_PROCESSORS="$2"
fi
ACTION="$3"
if [ -z "$ACTION" ]; then
  ACTION="create"
fi

if [ -z "$DATABASE_NAME" ] || [ -z "$PARALLEL_TEST_PROCESSORS" ] || (
  [ "$ACTION" != "create" ] && [ "$ACTION" != "drop" ]
); then
  echo "Usage: $0 <database name> <processors = \$PARALLEL_TEST_PROCESSORS> <action: create|drop = create>" >&2
  exit 1
fi

if [ "$ACTION" = "create" ]; then
  # Original db:structure:dump:
  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb#L49-L79
  DEV_DATABASE="${DATABASE_NAME}_development"
  DB_STRUCTURE_FILE="db/structure.sql"
  echo "Dumping ${DEV_DATABASE} schema to ${DB_STRUCTURE_FILE}..."
  pg_dump --schema-only "$DEV_DATABASE" > "$DB_STRUCTURE_FILE"
  # Remove initial comments (https://stackoverflow.com/a/17365113/304706)
  # See: https://github.com/rails/rails/blob/master/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb#L121-L136
  cat "$DB_STRUCTURE_FILE" | sed -n '/^SET/,$p' > "${DB_STRUCTURE_FILE}.uncommented"
  mv "${DB_STRUCTURE_FILE}.uncommented" "$DB_STRUCTURE_FILE"
  # Set search_path (always seems to be $user)
  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb#L78
  echo 'SET search_path TO "$user", public;' >> "$DB_STRUCTURE_FILE"
  # Dump schema information
  # https://github.com/rails/rails/blob/master/activerecord/lib/active_record/tasks/database_tasks.rb#L379-L385
  # * dump_schema_information: https://github.com/rails/rails/blob/b4ee2d5f6568a6edbf5ab521e6babd10639747f0/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb#L1070-L1073
  # * insert_versions_sql: https://github.com/rails/rails/blob/b4ee2d5f6568a6edbf5ab521e6babd10639747f0/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb#L1457-L1468
  pg_dump $DEV_DATABASE --data-only --table schema_migrations | sed -n '/^COPY/,$p' | grep -v '^--' \
    >> "$DB_STRUCTURE_FILE"
fi

for TEST_ENV_NUMBER in $(seq 1 $PARALLEL_TEST_PROCESSORS); do
  if [ "$TEST_ENV_NUMBER" = "1" ]; then TEST_ENV_NUMBER=""; fi
  DATABASE="${DATABASE_NAME}_test${TEST_ENV_NUMBER}"
  if [ "$ACTION" = "create" ]; then
    (
      echo "Creating $DATABASE..."
      createdb "${DATABASE}" || true
      echo "=> Loading ${DB_STRUCTURE_FILE} into ${DATABASE}..."
      cat "$DB_STRUCTURE_FILE" | psql "$DATABASE" -q > /dev/null
    ) &
  else
    (
      echo "Dropping $DATABASE..."
      dropdb "$DATABASE" || true
    ) &
  fi
done

wait
if [ "$ACTION" = "create" ]; then
  echo "Created $PARALLEL_TEST_PROCESSORS test databases!"
else
  echo "Dropped $PARALLEL_TEST_PROCESSORS test databases!"
fi