proposal: a validator for configuration files - Mailing list pgsql-hackers

Hi,

I'd like to add an ability to validate the corectness of PostgreSQL
configuration files, i.e. postgresql.conf, pg_hba.conf, pg_ident.conf without
actually applying them. The idea is that it would be a command-line option to
postgres for a stand-alone case, or a user-callable function when postmaster
is running.

Per the former discussion of a validator for PostgreSQL configuration files
(see http://archives.postgresql.org/pgsql-hackers/2008-08/msg00048.php),
here's an implementation proposal. The development plan consists of 2 parts.
The first one is to add new code that would allow running the checks in both a
stand-alone process, when postmaster is not running, and as a function call
from a backend postgres process. Initially the code would simply loads
configuration files, without performing any of the validation checks. The
second part consists of adding specific checks.

I think most of the code related to this feature should be put into the
auxiliary process. The rationale is that we already have a stand-alone
CheckerProcess, which nowadays only parses postgresql.conf, runs BaseInit and
exists. We can easily load pg_hba.conf and pg_ident.conf and run all the
necessary checks there. Moreover, the same process can be used when checks are
launched from a built-in function. In that case, it would save the postgres
backend from reloading postgresql.conf, pg_hba.conf and pg_ident.conf
internally and restoring the previous configuration options when the function
exists. Below is a more detailed description of implementation steps:

1.1. Stand-alone process (postmaster is not running):

- Add a new option (--check-config) to main.c. Run AuxiliaryProcessMain with auxType= CheckerProcess if this option is
specified.
- In CheckerModeMain load pg_hba.conf, pg_ident.conf


1.2. Built-in function, called from a backend process.
- Add a new built-in function
- Add LastCheckState shared flag to denote whether the check has been successful or failed
- Add a new PMSignalReason
- From the function call SendPostmasterSignal with the reason added on the previous step.
- In the postmaster add a check for this reason in sigusr1_handler, spawning a checker process. Set LastCheckStatus to
InProgress.
- Store current configuration options in AuxillaryProcessMain before reloading configuration files to avoid checking
foroptions that haven't changed. 
- In AuxillaryProcessMain, modify SelectConfigFiles invocation to call it if IsUnderPostmaster = true if auxType
processtype is CheckerProcess. 
- In the CheckerModeMain, set LastCheckState to either success or failure at the end of all checks.
- The built-in function would wait until LastCheckState changes its value from InProgress to either Succcess or
Failure,or until some predefined timeout expires, in which case it would emit an error. 

2. Add following configuration checks:

postgresql.conf:

Check that: 1. postgres can bind to listen address:port 2. unix_socket_directory has proper permissions (n/a on
Windows).3. unix_socket_group group exists on a target system (n/a Windows). 4. unix_socket_permissions are valid
(writepermission is not revoked from       the owner, or a group, if group is different from the user). 5. server.crt
andserver.key exist in the data directory if ssl is       set to true (and server is compiled with openssl) 6.
krb_server_keyfileis readable by the server (if  set) 7. server is not requesting more shared memory than it's
availablein the system. 8. shared_preload_libraries and local_preload_libraries exist. 9. synchronous_standby_names are
notempty and max_wal_senders       are > 0 if synchronous_replication = true 10. all enable_*  query planner parameters
areon. 11. seq_page_cost <= random_page_cost, and cpu_ costs are lower than page_ costs. 12. effective_cache_size is
lessthan the amount of physical memory available. 13. geqo is turned on 14. default_statistics_target is >= 100 15.
loggingcollector is enabled if log destination is stderr 16. log directory either exists and writable or that the
parent       directory allows creating subdris 17. track counts is on if autovacuum is enabled 18. stats_temp_directory
iswriteable 19. default tablespace exists (if set) 20. temp_tablespace exists (if set) 21. statement_timeout is 0
(disabled)22. dynamic_library_path exists 23. sql_inheritance is off 24. zero_damaged_pages is off         
pg_hba.conf:
Check that: 1. the server is compiled with ssl if hostssl is specified 2. ssl is not required if hostnossl is specified

- Add a Warning value to LastCheckState for cases when configuration
files were loaded successfully, but one or more validation checks have failed.

Note that these are basic checks don't require the checker process to have
access to the database, Also, with this implementation, a client won't receive
an exact error message in case validation is unsuccessful, however, it would
receive a status (success, failure, warnings), and an exact error message
would be available in the server's log. It's possible to address these
shortcomings in the future.

Ideas, suggestions are welcome.

--
Alexey Klyukin
The PostgreSQL Company - Command Prompt, Inc.