Re: exposing pg_controldata and pg_config as functions

On 09/06/2015 12:34 PM, Joe Conway wrote:
> To the extent that we want specific pg_controldata output in non-text
> form, we should identify which items those are and provide individual
> functions for them.

Well, I think it's pretty simple, let's take it down:

# function pg_control_control_data() returning INT, TSTZ
pg_control version number: 942
pg_control last modified: Thu 20 Aug 2015 10:05:33 AM PDT

#function pg_catversion() returning BIGINT
Catalog version number: 201409291

# have function for this, no?
Database system identifier: 6102142380557650900

# not relevant, if we can connect, it's running
Database cluster state: shut down

# Do we have functions for all of the below?
# if not I suggest virtual table pg_checkpoint_status
# returning the below 17 columns
# that would be useful even if we have some of them
Latest checkpoint location: 0/1A1BF178
Prior checkpoint location: 0/1A1BF0D8
Latest checkpoint's REDO location: 0/1A1BF178
Latest checkpoint's REDO WAL file: 00000001000000000000001A
Latest checkpoint's TimeLineID: 1
Latest checkpoint's PrevTimeLineID: 1
Latest checkpoint's full_page_writes: on
Latest checkpoint's NextXID: 0/2038
Latest checkpoint's NextOID: 19684
Latest checkpoint's NextMultiXactId: 1
Latest checkpoint's NextMultiOffset: 0
Latest checkpoint's oldestXID: 711
Latest checkpoint's oldestXID's DB: 1
Latest checkpoint's oldestActiveXID: 0
Latest checkpoint's oldestMultiXid: 1
Latest checkpoint's oldestMulti's DB: 1
Time of latest checkpoint: Thu 20 Aug 2015 10:05:33 AM PDT

# Not in any way useful
Fake LSN counter for unlogged rels: 0/1

# add another system view,
# pg_recovery_state, holding the
# below 5 columns
Minimum recovery ending location: 0/0
Min recovery ending loc's timeline: 0
Backup start location: 0/0
Backup end location: 0/0
End-of-backup record required: no

# duplicates system settings, not needed
Current wal_level setting: logical
Current wal_log_hints setting: off
Current max_connections setting: 100
Current max_worker_processes setting: 8
Current max_prepared_xacts setting: 0
Current max_locks_per_xact setting: 64
Maximum data alignment: 8
Database block size: 8192

# do we have the below anywhere else?
# this is somewhat duplicative of config info
Blocks per segment of large relation: 131072
WAL block size: 8192
Bytes per WAL segment: 16777216
Maximum length of identifiers: 64
Maximum columns in an index: 32
Maximum size of a TOAST chunk: 1996
Size of a large-object chunk: 2048
Date/time type storage: 64-bit integers
Float4 argument passing: by value
Float8 argument passing: by value

# return INT function pg_data_page_checksum_version()
Data page checksum version: 0

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com