Authentication failures and related problems generally manifest themselves through error messages like the following: FATAL: no pg_hba.conf entry for host "123.123.123.123", user "andym", database "testdb" This is what you are most likely to get if you succeed in contacting the server, but it does not want to talk to you. As the message suggests, the server refused the connection request because it found no matching entry in its pg_hba.conf configuration file. FATAL: password authenticatio

The view pg_group exists for backwards compatibility: it emulates a catalog that existed in PostgreSQL before version 8.1. It shows the names and members of all roles that are marked as not rolcanlogin, which is an approximation to the set of roles that are being used as groups. Table 50-64. pg_group Columns Name Type References Description groname name pg_authid.rolname Name of the group grosysid oid pg_authid.oid ID of this group grolist oid[] pg_authid.oid An array containing the IDs of th

A database is a named collection of SQL objects ("database objects"). Generally, every database object (tables, functions, etc.) belongs to one and only one database. (However there are a few system catalogs, for example pg_database, that belong to a whole cluster and are accessible from each database within the cluster.) More accurately, a database is a collection of schemas and the schemas contain the tables, functions, etc. So the full hierarchy is: server, database, schema, table (or some o

PostgreSQL provides a rich set of tools for developers to manage concurrent access to data. Internally, data consistency is maintained by using a multiversion model (Multiversion Concurrency Control, MVCC). This means that each SQL statement sees a snapshot of data (a database version) as it was some time ago, regardless of the current state of the underlying data. This prevents statements from viewing inconsistent data produced by concurrent transactions performing updates on the same data row

NameMOVE -- position a cursor Synopsis MOVE [ direction [ FROM | IN ] ] cursor_name where direction can be empty or one of: NEXT PRIOR FIRST LAST ABSOLUTE count RELATIVE count count ALL FORWARD FORWARD count FORWARD ALL BACKWARD BACKWARD count BACKWARD ALL Description MOVE repositions a cursor without retrieving any data. MOVE works exactly like the FETCH command, except it only positions the cursor and does not return rows. Th

PostgreSQL offers data types to store IPv4, IPv6, and MAC addresses, as shown in Table 8-21. It is better to use these types instead of plain text types to store network addresses, because these types offer input error checking and specialized operators and functions (see Section 9.12). Table 8-21. Network Address Types Name Storage Size Description cidr 7 or 19 bytes IPv4 and IPv6 networks inet 7 or 19 bytes IPv4 and IPv6 hosts and networks macaddr 6 bytes MAC addresses When sorting inet or

The catalog pg_tablespace stores information about the available tablespaces. Tables can be placed in particular tablespaces to aid administration of disk layout. Unlike most system catalogs, pg_tablespace is shared across all databases of a cluster: there is only one copy of pg_tablespace per cluster, not one per database. Table 50-47. pg_tablespace Columns Name Type References Description oid oid Row identifier (hidden attribute; must be explicitly selected) spcname name Tablespace name

The date/time type inputs are all decoded using the following procedure. Break the input string into tokens and categorize each token as a string, time, time zone, or number. If the numeric token contains a colon (:), this is a time string. Include all subsequent digits and colons. If the numeric token contains a dash (-), slash (/), or two or more dots (.), this is a date string which might have a text month. If a date token has already been seen, it is instead interpreted as a time zone

61.4.1. GiST buffering build Building large GiST indexes by simply inserting all the tuples tends to be slow, because if the index tuples are scattered across the index and the index is large enough to not fit in cache, the insertions need to perform a lot of random I/O. Beginning in version 9.2, PostgreSQL supports a more efficient method to build GiST indexes based on buffering, which can dramatically reduce the number of random I/Os needed for non-ordered data sets. For well-ordered data se

In the previous chapter we have covered the basics of using SQL to store and access your data in PostgreSQL. We will now discuss some more advanced features of SQL that simplify management and prevent loss or corruption of your data. Finally, we will look at some PostgreSQL extensions. This chapter will on occasion refer to examples found in Chapter 2 to change or improve them, so it will be useful to have read that chapter. Some examples from this chapter can also be found in advanced.sql in t