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ftp://ftp.kr.postgresql.org/.3/postgresql/source/v7.4/

                               Release Notes
                                      
                                Release 7.4
                                      
     Release date: 2003-11-17
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                                  Overview
                                      
   Major changes in this release:
   
   IN/NOT IN subqueries are now much more efficient
          In previous releases, IN/NOT IN subqueries were joined to the
          upper query by sequentially scanning the subquery looking for a
          match. The 7.4 code uses the same sophisticated techniques used
          by ordinary joins and so is much faster. An IN will now usually
          be as fast as or faster than an equivalent EXISTS subquery;
          this reverses the conventional wisdom that applied to previous
          releases.
          
   Improved GROUP BY processing by using hash buckets
          In previous releases, rows to be grouped had to be sorted
          first. The 7.4 code can do GROUP BY without sorting, by
          accumulating results into a hash table with one entry per
          group. It will still use the sort technique, however, if the
          hash table is estimated to be too large to fit in sort_mem.
          
   New multikey hash join capability
          In previous releases, hash joins could only occur on single
          keys. This release allows multicolumn hash joins.
          
   Queries using the explicit JOIN syntax are now better optimized
          Prior releases evaluated queries using the explicit JOIN syntax
          only in the order implied by the syntax. 7.4 allows full
          optimization of these queries, meaning the optimizer considers
          all possible join orderings and chooses the most efficient.
          Outer joins, however, must still follow the declared ordering.
          
   Faster and more powerful regular expression code
          The entire regular expression module has been replaced with a
          new version by Henry Spencer, originally written for Tcl. The
          code greatly improves performance and supports several flavors
          of regular expressions.
          
   Function-inlining for simple SQL functions
          Simple SQL functions can now be inlined by including their SQL
          in the main query. This improves performance by eliminating
          per-call overhead. That means simple SQL functions now behave
          like macros.
          
   Full support for IPv6 connections and IPv6 address data types
          Previous releases allowed only IPv4 connections, and the IP
          data types only supported IPv4 addresses. This release adds
          full IPv6 support in both of these areas.
          
   Major improvements in SSL performance and reliability
          Several people very familiar with the SSL API have overhauled
          our SSL code to improve SSL key negotiation and error recovery.
          
   Make free space map efficiently reuse empty index pages, and other
          free space management improvements
          In previous releases, B-tree index pages that were left empty
          because of deleted rows could only be reused by rows with index
          values similar to the rows originally indexed on that page. In
          7.4, "VACUUM" records empty index pages and allows them to be
          reused for any future index rows.
          
   SQL-standard information schema
          The information schema provides a standardized and stable way
          to access information about the schema objects defined in a
          database.
          
   Cursors conform more closely to the SQL standard
          The commands "FETCH" and "MOVE" have been overhauled to conform
          more closely to the SQL standard.
          
   Cursors can exist outside transactions
          These cursors are also called holdable cursors.
          
   New client-to-server protocol
          The new protocol adds error codes, more status information,
          faster startup, better support for binary data transmission,
          parameter values separated from SQL commands, prepared
          statements available at the protocol level, and cleaner
          recovery from "COPY" failures. The older protocol is still
          supported by both server and clients.
          
   libpq and ECPG applications are now fully thread-safe
          While previous libpq releases already supported threads, this
          release improves thread safety by fixing some non-thread-safe
          code that was used during database connection startup. The
          "configure" option "--enable-thread-safety" must be used to
          enable this feature.
          
   New version of full-text indexing
          A new full-text indexing suite is available in
          "contrib/tsearch2".
          
   New autovacuum tool
          The new autovacuum tool in "contrib/autovacuum" monitors the
          database statistics tables for "INSERT"/"UPDATE"/"DELETE"
          activity and automatically vacuums tables when needed.
          
   Array handling has been improved and moved into the server core
          Many array limitations have been removed, and arrays behave
          more like fully-supported data types.
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