Re: Incomplete description of pg_start_backup?

I think that at http://www.postgresql.org/docs/current/static/functions-admin.html and http://www.postgresql.org/docs/current/static/continuous-archiving.html two important points on how pg_start_backup() works are missing:

1. After pg_start_backup() and till pg_stop_backup() VACUUM is denied (e.g. autovacuum is turned off), so the new data is always appended to data files, is never written at their middle.

This allows to archive the data directory using any copying tools (rsync, tar, cp etc.). If you forget to call pg_stop_backup() by accident, data files will grow forever. So pg_start_backup() switches the database to "append-only mode" which is safe to backup without stopping (data files temporarily become append-only, WAL logs are append-only always).

2. After pg_start_backup() and till pg_stop_backup() full_page_writes is forced to be ON.