Postgres functions for disk monitoring, etc

pg_functions

# postgres mgmt funcitons

## show total_bytes, index_bytes

  SELECT c.oid,
		  nspname AS table_schema, 
		  relname AS TABLE_NAME, 
		  c.reltuples AS row_estimate,
		  pg_size_pretty(pg_total_relation_size(c.oid)) AS total_bytes,
		  pg_size_pretty(pg_indexes_size(c.oid)) AS index_bytes
	FROM pg_class c
	LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
	WHERE relkind = 'r'	
	ORDER BY row_estimate DESC;

	 oid   |    table_schema    |        table_name         | row_estimate | total_bytes | index_bytes
	--------+--------------------+---------------------------+--------------+-------------+-------------
	 302543 | dfms_20800         | gps_histories             |  1.86702e+07 | 12 GB       | 2573 MB
	 282734 | dfms_10324         | gps_histories             |  1.63947e+07 | 10167 MB    | 2226 MB
	 304958 | dfms_30500         | gps_histories             |  1.16624e+07 | 7400 MB     | 1582 MB
	 293366 | dfms_10731         | gps_histories             |  9.78157e+06 | 6068 MB     | 1327 MB
	 303026 | dfms_20900         | gps_histories             |  6.79223e+06 | 4372 MB     | 935 MB
	 305927 | dfms_30700         | gps_histories             |  5.14508e+06 | 3253 MB     | 708 MB
	 284183 | dfms_10401         | gps_histories             |  4.42729e+06 | 2769 MB     | 605 MB
	 300128 | dfms_10977         | gps_histories             |   3.9728e+06 | 2481 MB     | 544 MB
	 286115 | dfms_10522         | gps_histories             |   3.9027e+06 | 2491 MB     | 529 MB
	 290460 | dfms_10665         | gps_histories             |  3.46105e+06 | 2210 MB     | 477 MB

## total index

SELECT pg_size_pretty(SUM(pg_indexes_size(c.oid)))
FROM pg_class c
LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
WHERE relkind = 'r';	 

## timestamp => date
SELECT extract(epoch from '2018-03-30T00:00:00+00' AT TIME ZONE 'UTC');