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<appendix id="release">

In previous releases, IN/NOT IN subqueries were joined to the

upper query by sequentially scanning the subquery looking for

a join. The 7.4 code uses the same sophisticated techniques

used by ordinary joins and so is much faster, and is now faster

than EXISTS subqueries.

used by ordinary joins and so is much faster. An IN

will now usually as fast as or faster than an equivalent EXISTS

subquery; this reverses the conventional wisdom that applied to

previous releases.

</para>

</listitem>

<listitem><para> Improved GROUP BY processing by using hash buckets</para>

<para>

In previous releases, GROUP BY totals were accumulated by

sequentially scanning the list of groups looking for a match;

the 7.4 code places GROUP BY values in hash buckets so the

proper match can be found much quicker. This is particularly

significant in speeding up queries that have a large

number of distinct GROUP BY values.

In previous releases, GROUP BY values were accumulated and sorted

to obtain group-by counts; the 7.4 code places GROUP BY values in

hash buckets so sorting is not required, or reverts to the old

behavior if the group-by buckets will not fit in memory.

</para>

</listitem>

specified by the query; 7.4 allows full optimization of

queries using ANSI join syntax, meaning the optimizer considers

all possible join orderings and chooses the most efficient.

Outer joins, however, must still follow the declared ordering.

</para>

</listitem>

<listitem><para> Full support for IPv6 connections and IPv6 address

data types</para>

<para>

Prior releases allowed onlyIPv6 connections and IP data types only

Prior releases allowed onlyIPv4 connections and IP data types only

supported IPv4 addresses. This release adds full IPv6 support in

both of these areas.

</para>

</para>

</listitem>

<listitem><para> New protocol improves connection speed/reliability,

and adds error codes, status information, a binary protocol, error

reporting verbosity, and cleaner startup packets.</para>

<listitem><para> New client-to-server protocol adds error codes, more status

information, better support for binary data transmission, parameter

values separated from SQL commands, prepared statements available at the

protocol level, clean recovery from COPY failures, and cleaner startup

packets. The older protocol is still supported by both servers and

clients.

</para>

</listitem>

<listitem><para> Allow cursors to exist outside transactions,

systems.

</para>

</listitem>

<listitem><para>Syntax errors now reported as 'syntax error' rather than 'parse error' (Tom)</para></listitem>

</itemizedlist></para></sect2>

<sect2><title> Server Operation Changes</title>

</listitem>

<listitem><para>Align shared buffers on 32-byte boundary for copy speed improvement (Manfred Spraul)</para>

<para>

Certain CPU's perform faster data copies when addresses are 32-bit

Certain CPU's perform faster data copies when addresses are 32-byte

aligned.

</para>

</listitem>

strings.

</para>

</listitem>

<listitem><para>Fixsubqueryaggregatesof upper query columnsto match SQL spec. (Tom)</para>

<listitem><para>Fix aggregatesin subqueriesto match SQL spec (Tom)</para>

<para>

bjm

The SQL spec says that an aggregate function appearing within a nested

subquery belongs to the outer query if its argument contains only

outer-query variables. Prior PG releases did not handle this fine point

correctly.

</para>

</listitem>

<listitem><para>Add option to prevent auto-addition of tables referenced in query (Nigel J.

Andrews) </para>

<para>

By default, tables mentioned in the query are automatically added

to the FROM clause if they are not already there. This option

disabled that behavior.

to the FROM clause if they are not already there. This is compatible with

historic Postgres behavior but is contrary to the SQL spec.

This option allows selecting spec-compatible behavior.

</para>

</listitem>

<listitem><para>Allow UPDATE ... SET col = DEFAULT (Rod)</para>

the transaction aborts.

</para>

</listitem>

<listitem><para>Multiplepggla_dump fixes, including tar format and large objects</para></listitem>

<listitem><para>Multiplepg_dump fixes, including tar format and large objects</para></listitem>

<listitem><para>Allow pg_dump to dump specific schemas (Neil)</para></listitem>

<listitem><para>Allow pg_dump to preserve column storage characteristics (Christopher)</para>

<para>