Vamos nos concentrar no primeiro exemplo: postgresql-contrib
Este meta-pacote sempre depende do pacote de contribuição de banco de dados do PostgreSQL atualmente suportado.
A palavra-chave aqui é que é um meta-pacote . Você encontrará muitas instâncias de meta-pacotes no repositório. Por si só, os metapacotes realmente não contêm nada, então não há nada para documentar exceto o pacote para o qual ele aponta. Se você olhar as informações fornecidas por apt-cache show postgresql-contrib
novamente, perceberá que há uma linha que mostra:
Depende: postgresql-contrib-9.5
A documentação atual que você precisa ver está contida neste pacote. O seguinte é o resultado de apt-cache show postgresql-contrib-9.5
:
Package: postgresql-contrib-9.5
Priority: optional
Section: database
Installed-Size: 1999
Maintainer: Ubuntu Developers <[email protected]>
Original-Maintainer: Debian PostgreSQL Maintainers <[email protected]>
Architecture: amd64
Source: postgresql-9.5
Version: 9.5.6-0ubuntu0.16.04
Depends: postgresql-9.5 (= 9.5.6-0ubuntu0.16.04), libc6 (>= 2.15), libpq5 (>= 9.2~beta3), libselinux1 (>= 2.1.12), libssl1.0.0 (>= 1.0.0), libuuid1 (>= 2.16), libxml2 (>= 2.7.4), libxslt1.1 (>= 1.1.25), zlib1g (>= 1:1.1.4)
Suggests: libdbd-pg-perl
Filename: pool/main/p/postgresql-9.5/postgresql-contrib-9.5_9.5.6-0ubuntu0.16.04_amd64.deb
Size: 446848
MD5sum: a05acc14f59c7d0f98bfc854a90447d7
SHA1: 398b18b8660537ac114eceb1212ff831d911c856
SHA256: 6ef4578df2026a72e9c85715ea112f4077209490beb18e3e715621319d5861f0
Description-en: additional facilities for PostgreSQL
The PostgreSQL contrib package provides several additional features
for the PostgreSQL database. This version is built to work with the
server package postgresql-9.5. contrib often serves as a testbed for
features before they are adopted into PostgreSQL proper:
.
adminpack - File and log manipulation routines, used by pgAdmin
btree_gist - B-Tree indexing using GiST (Generalised Search Tree)
chkpass - An auto-encrypted password datatype
cube - Multidimensional-cube datatype (GiST indexing example)
dblink - Functions to return results from a remote database
earthdistance - Operator for computing the distance (in miles) between
two points on the earth's surface
fuzzystrmatch - Levenshtein, metaphone, and soundex fuzzy string matching
hstore - Store (key, value) pairs
intagg - Integer aggregator/enumerator
_int - Index support for arrays of int4, using GiST (benchmark
needs the libdbd-pg-perl package)
isn - type extensions for ISBN, ISSN, ISMN, EAN13 product numbers
lo - Large Object maintenance
ltree - Tree-like data structures
oid2name - Maps OIDs to table names
pageinspect - Inspection of database pages
passwordcheck - Simple password strength checker
pg_buffercache - Real time queries on the shared buffer cache
pg_freespacemap- Displays the contents of the free space map (FSM)
pg_trgm - Determine the similarity of text based on trigram matching
pg_standby - Create a warm stand-by server
pgbench - TPC-B like benchmark
pgcrypto - Cryptographic functions
pgrowlocks - A function to return row locking information
pgstattuple - Returns the percentage of dead tuples in a table; this
indicates whether a vacuum is required.
postgresql_fdw - foreign data wrapper for PostgreSQL
seg - Confidence-interval datatype (GiST indexing example)
sepgsql - mandatory access control (MAC) based on SELinux
spi - PostgreSQL Server Programming Interface; 4 examples of
its use:
autoinc - A function for implementing AUTOINCREMENT/
IDENTITY
insert_username - function for inserting user names
moddatetime - Update modification timestamps
refint - Functions for implementing referential
integrity (foreign keys). Note that this is
now superseded by built-in referential
integrity.
timetravel - Re-implements in user code the time travel
feature that was removed in 6.3.
tablefunc - examples of functions returning tables
uuid-ossp - UUID generation functions
vacuumlo - Remove orphaned large objects
.
PostgreSQL is an object-relational SQL database management system.
Description-md5: 633a4e0645b2b02e72f77a260d0f4030
Homepage: http://www.postgresql.org/
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Origin: Ubuntu
Supported: 5y
Task: postgresql-server
Você notará que a documentação do pacote atual é muito mais detalhada.