Module Name:	pkgsrc
Committed By:	uebayasi
Date:		Mon Mar 20 14:51:22 UTC 2006

Modified Files:
	pkgsrc/doc: CHANGES

Log Message:
Note initial import of PostgreSQL 8.1.3, from pkgsrc-wip.

This is an overview of new features in 8.1.0 against 8.0.x.  8.1.3 includes
many bug fixes since 8.1.0.  Please read documentation of the detailed changes
and procedure of data migration.

Overview

   Major changes in this release:

   Improve concurrent access to the shared buffer cache (Tom)
          Access to the shared buffer cache was identified as a
          significant scalability problem, particularly on multi-CPU
          systems. In this release, the way that locking is done in the
          buffer manager has been overhauled to reduce lock contention and
          improve scalability. The buffer manager has also been changed to
          use a "clock sweep" replacement policy.

   Allow index scans to use an intermediate in-memory bitmap (Tom)
          In previous releases, only a single index could be used to do
          lookups on a table. With this feature, if a query has "WHERE
          tab.col1 = 4 and tab.col2 = 9", and there is no multicolumn
          index on col1 and col2, but there is an index on col1 and
          another on col2, it is possible to search both indexes and
          combine the results in memory, then do heap fetches for only the
          rows matching both the col1 and col2 restrictions. This is very
          useful in environments that have a lot of unstructured queries
          where it is impossible to create indexes that match all possible
          access conditions. Bitmap scans are useful even with a single
          index, as they reduce the amount of random access needed; a
          bitmap index scan is efficient for retrieving fairly large
          fractions of the complete table, whereas plain index scans are
          not.

   Add two-phase commit (Heikki Linnakangas, Alvaro, Tom)
          Two-phase commit allows transactions to be "prepared" on several
          computers, and once all computers have successfully prepared
          their transactions (none failed), all transactions can be
          committed. Even if a machine crashes after a prepare, the
          prepared transaction can be committed after the machine is
          restarted. New syntax includes "PREPARE TRANSACTION" and
          "COMMIT/ROLLBACK PREPARED". A new system view pg_prepared_xacts
          has also been added.

   Create a new role system that replaces users and groups (Stephen Frost)
          Roles are a combination of users and groups. Like users, they
          can have login capability, and like groups, a role can have
          other roles as members. Roles basically remove the distinction
          between users and groups. For example, a role can:

          + Have login capability (optionally)
          + Own objects
          + Hold access permissions for database objects
          + Inherit permissions from other roles it is a member of

          Once a user logs into a role, she obtains capabilities of the
          login role plus any inherited roles, and can use "SET ROLE" to
          switch to other roles she is a member of. This feature is a
          generalization of the SQL standard's concept of roles. This
          change also replaces pg_shadow and pg_group by new role-capable
          catalogs pg_authid and pg_auth_members. The old tables are
          redefined as read-only views on the new role tables.

   Automatically use indexes for MIN() and MAX() (Tom)
          In previous releases, the only way to use an index for MIN() or
          MAX() was to rewrite the query as "SELECT col FROM tab ORDER BY
          col LIMIT 1". Index usage now happens automatically.

   Move /contrib/pg_autovacuum into the main server (Alvaro)
          Integrating autovacuum into the server allows it to be
          automatically started and stopped in sync with the database
          server, and allows autovacuum to be configured from
          "postgresql.conf".

   Add shared row level locks using SELECT ... FOR SHARE (Alvaro)
          While PostgreSQL's MVCC locking allows "SELECT" to never be
          blocked by writers and therefore does not need shared row locks
          for typical operations, shared locks are useful for applications
          that require shared row locking. In particular this reduces the
          locking requirements imposed by referential integrity checks.

   Add dependencies on shared objects, specifically roles (Alvaro)
          This extension of the dependency mechanism prevents roles from
          being dropped while there are still database objects they own.
          Formerly it was possible to accidentally "orphan" objects by
          deleting their owner. While this could be recovered from, it was
          messy and unpleasant.

   Improve performance for partitioned tables (Simon)
          The new constraint_exclusion configuration parameter avoids
          lookups on child tables where constraints indicate that no
          matching rows exist in the child table.

          This allows for a basic type of table partitioning. If child
          tables store separate key ranges and this is enforced using
          appropriate "CHECK" constraints, the optimizer will skip child
          table accesses when the constraint guarantees no matching rows
          exist in the child table.


To generate a diff of this commit:
cvs rdiff -r1.13340 -r1.13341 pkgsrc/doc/CHANGES

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.