PG_STAT_DATABASE

I am looking into the PostgreSQL dictionary. The view pg_stat_activity
is the PgSQL version of v$session. There are interesting views named
pg_stat_database and pg_stat_user_tables. What is the starting point for
those stat views? Is that since the database and table, in case of the
latter view, was created? Is it since the last restart of the instance?
I was unable to find that in the documentation.
Here is the description of the view in question:

View "pg_catalog.pg_stat_database"
Column | Type | Modifiers
---------------+---------+-----------
datid | oid |
datname | name |
numbackends | integer |
xact_commit | bigint |
xact_rollback | bigint |
blks_read | bigint |
blks_hit | bigint |
tup_returned | bigint |
tup_fetched | bigint |
tup_inserted | bigint |
tup_updated | bigint |
tup_deleted | bigint |

VMS
Mladen Gogala
Sr. Oracle DBA
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(212) 329-5251
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