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Typical markup:
<note>
<title>Release date</title>
- <simpara>2007-??-??</simpara>
+ <simpara>2007-12-??</simpara>
<para>CURRENT AS OF 2007-10-03</>
</note>
<title>Overview</title>
<para>
- This release adds many improvements that were requested by users,
- including:
+ This release represents a major leap forward by adding significant
+ new functionality and performance enhancements to
+ <productname>PostgreSQL</>. Many complex ideas that normally take
+ years to implement were added rapidly to this release by our
+ development team. This release starts <productname>PostgreSQL</> on
+ a trajectory moving beyond feature-parity with other database
+ systems to a time when <productname>PostgreSQL</> will be a
+ technology leader in the database field. Major new capabilities
+ this release include:
<itemizedlist>
<listitem>
<para>
- Full text search is now a built-in feature
+ Full text search now fully integrated into the core database
+ system
</para>
</listitem>
<listitem>
<para>
- Support for the SQL/XML standard, including a new <type>xml</type> builtin
+ Support for the SQL/XML standard, including a new <type>XML</type> builtin
data type
</para>
</listitem>
<listitem>
<para>
- enum data types
+ Enumerated (<type>ENUM</>) data type support
+ </para>
+
+ <para>
+ This is accomplished by creating a new data type with an
+ <literal>ENUM</> clause, e.g.
+ <literal>CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy')</>.
</para>
</listitem>
<listitem>
<para>
- UUID data type, similar to that defined by RFC 4122
+ Universally Unique Identifier (UUID) data type, similar to that
+ defined by RFC 4122
</para>
</listitem>
<listitem>
<para>
+ Control of whether <literal>NULL</>s sort first or last, using
<literal>ORDER BY ... NULLS FIRST/LAST</>
</para>
</listitem>
<listitem>
<para>
- Updatable cursors
- (<literal>UPDATE/DELETE WHERE CURRENT OF</>
- <replaceable>cursor_name</>)
+ Updatable cursors using <literal>UPDATE/DELETE WHERE CURRENT OF</>
+ </para>
+
+ <para>
+ This eliminates the need to reference a primary key to update or
+ delete rows returned by a cursor.
</para>
</listitem>
<listitem>
<para>
- Per-function parameter settings
+ Server configuration parameters can now be set on a per-function
+ basis
+ </para>
+
+ <para>
+ For example, functions can now set their own
+ <varname>search_path</> to prevent unexpected behavior if a
+ different <varname>search_path</> exists at run-time.
</para>
</listitem>
<listitem>
<para>
- User-defined types can now have type modifiers (parameters)
+ User-defined types can now have type modifiers
</para>
<para>
- Declarations such as <type>varchar(42)</type> are no longer
- restricted to use by built-in data types.
+ This allows a user type to take a modifier when
+ being referenced, e.g. <type>SSNUM(7)</>. Previously only
+ predefined system data types would allow this, e.g.
+ <type>CHAR(4)</>.
</para>
</listitem>
<listitem>
<para>
- Automatic plan invalidation when table definitions change
+ Automatically invalidate cached function code when table
+ definitions change
</para>
<para>
- This will particularly ease usage of temporary tables in
- PL/PgSQL functions.
+ Previously PL/pgSQL functions that referenced temporary tables
+ would fail if the temporary table was dropped and recreated
+ between function invocations, unless <literal>EXECUTE</> was
+ used.
</para>
</listitem>
<listitem>
<para>
- Numerous improvements in logging and statistics collection
- capabilities, including the ability to emit postmaster log messages
- in CSV format that can be directly loaded into a database table
- for analysis
+ Numerous improvements in logging and statistics collection,
+ including the ability to emit postmaster log messages in
+ <acronym>CSV</> format, which can be loaded into a database
+ table for analysis
</para>
</listitem>
<para>
SSPI/GSSAPI authentication support
</para>
+
+ <para>
+ This adds native Security Service Provider Interface (SSPI) for
+ Windows.
+ </para>
</listitem>
<listitem>
</para>
<para>
- Autovacuum is now considered mature enough to be enabled by default.
+ This allows multiple vacuums to run concurrently, meaning
+ vacuuming of a large table will not prevent smaller tables from
+ being vacuumed at the same time. Autovacuum is now considered
+ mature and thus enabled by default.
</para>
</listitem>
<listitem>
<para>
- The entire <productname>PostgreSQL</productname> system can
- now be compiled with Microsoft Visual C++
+ The backend database server can now be compiled with
+ <productname>Microsoft Visual C++</>
</para>
<para>
- This will improve the ability of Windows-based developers to
- contribute to the project. Windows executables made with Visual C++
- may also have better stability and performance than those made with
- other tool sets.
+ Windows executables made with Visual C++ might have better
+ stability and performance than those made with other tool sets.
+ Development and debugging tools familiar to Windows developers
+ will also work.
</para>
</listitem>
</itemizedlist>
- Major performance improvements in this release include:
+ Major performance improvements are listed below. Fortunately, most
+ of these enhancements are automatic and require user changes or
+ tuning:
<itemizedlist>
<listitem>
<para>
- Asynchronous commit option to allow transactions to be reported
- committed before they have actually been flushed to disk
+ Asynchronous commit option allows transactions to be committed
+ but on-disk changes to be delayed
</para>
<para>
- This would not, of course, be acceptable if the client takes some
- critical external action on the assumption that the transaction
- will be remembered; but for certain applications, it is an acceptable
- risk for some or all transactions to use this mode. Unlike existing
- options such as <varname>fsync</varname>, asynchronous commit does
- not risk database corruption; the worst case is that after a crash,
- the last few reportedly-committed transactions will not have
- taken effect.
+ This feature dramatically increases performance for data
+ modification queries. The disadvantage is that because on-disk
+ changes are delayed, if the operating system crashes before data
+ is written to the disk, committed data will be lost. This is
+ useful only for applications that can accept some data loss.
+ Unlike <varname>fsync</varname>, asynchronous commit does not
+ risk database corruption; the worst case is that after an
+ operating system crash the last few reportedly-committed
+ transactions will be missing.
</para>
</listitem>
<listitem>
<para>
- <quote>Distributed</> checkpoints to spread out the I/O load of a
- checkpoint
+ <quote>Distributed</> checkpoints prevent I/O spikes during
+ checkpoints
+ </para>
+
+ <para>
+ Previously all modified buffers were forced to disk at
+ checkpoint time, causing an I/O spike and decreasing server
+ performance. This new capability spreads checkpoint activity out
+ between checkpoints, reducing peak I/O usage.
</para>
</listitem>
<listitem>
<para>
- Heap-Only Tuples (HOT) to reduce overhead of updates
+ Heap-Only Tuples (<acronym>HOT</>) improves <command>UPDATE</>
+ space usage
+ </para>
+
+ <para>
+ To allow high concurrency <productname>PostgreSQL</> retains old
+ versions of updated rows. Previously only <command>VACUUM</>
+ could reuse space taken by dead rows. With <acronym>HOT</> dead
+ row space can be reused at the time of <command>UPDATE</> or
+ <command>INSERT</>. This allows for more consistent performance.
+ <acronym>HOT</> also improved deleted row space reuse.
</para>
</listitem>
Just-in-time background writer strategy to improve disk write
efficiency
</para>
+
+ <para>
+ This basically makes the background writer self-tuning.
+ </para>
+
</listitem>
<listitem>
<para>
- Reduction of on-disk data size through reducing both per-tuple
- and per-field overheads
+ Reduction of both per-field and per-row storage requirements
+ </para>
+
+ <para>
+ Variable-length data types with data values less then 128 bytes
+ will see a decrease of 3-6 bytes. For example, two
+ <type>CHAR(1)</type> fields now take 4 bytes instead of 16. Rows
+ are also 4 bytes shorter.
</para>
</listitem>
<listitem>
<para>
- Efficiency improvements for large sequential scans, including
- prevention of cache flushing and <quote>piggybacking</quote> to let
- concurrent scans read the table only once
+ Prevent large sequential scans from forcing out more frequently
+ used cached pages
</para>
</listitem>
<listitem>
<para>
- Top-N sorting
+ Allow large sequential scans to use cached pages from other
+ concurrent sequential scans
+ </para>
+
+ <para>
+ This is accomplished by starting the new sequential scan in the
+ middle of the table (where the other sequential scan is already
+ in-progress) and wrapping around to the beginning to finish.
</para>
</listitem>
<listitem>
<para>
- Lazy XID assignment to reduce the cost of read-only transactions
+ Allow <literal>ORDER BY ... LIMIT</> to be done without sorting
</para>
<para>
- For applications in which there are a large number of read-only
- transactions, this helps not only by reducing overhead for the
- transactions themselves, but by reducing overhead that's driven
- by the rate of XID consumption; notably, reducing contention for
- transaction log buffers and reducing the frequency of
- anti-wraparound vacuuming.
+ This is done by scanning the table and using a filter to find
+ the few requested rows, rather than sorting the entire table.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ Use pseudo-transaction ids in read-only transactions
+ </para>
+
+ <para>
+ This reduces transaction overhead for read-only transactions,
+ and reduces the need for vacuuming for transaction id
+ wrap-around.
</para>
</listitem>
<listitem>
<para>
- <filename>contrib/tsearch2</> features have been absorbed into
- the core, with some syntax changes
+ <filename>contrib/tsearch2</> features have been moved into
+ the core server, with some minor syntax changes
</para>
<para>
<listitem>
<para>
- Casts to <type>text</type> that formerly occurred implicitly may now
- need to be written explicitly
+ Queries that previously automatically cast values to
+ <type>TEXT</type> might now need explicit casts
</para>
<para>
- Data types other than <type>char</> and <type>varchar</> are no
- longer implicitly castable to <type>text</>, except in the limited
- case of a <literal>||</> (concatenation) operator whose other
- input is textual. While this will require explicit casts in a
- few queries that didn't need them before, the elimination of
- surprising interpretations justifies it.
+ Data types other than <type>CHAR</> and <type>VARCHAR</> no
+ longer automatically cast to <type>TEXT</>, except in the
+ limited case of concatenation (<literal>||</>) where the other
+ input is textual. While this change will require additional
+ casts for some queries it also eliminates some unusual
+ behavior.
</para>
</listitem>
<listitem>
<para>
- Numerous changes in administrator-only configuration parameters
+ Numerous changes in administrative server parameters
</para>
<para>
<varname>track_activities</>.
<varname>stats_block_level</> and <varname>stats_row_level</>
are merged into <varname>track_counts</>.
- <varname>archive_command</> changed meaning slightly: you must now set
- <varname>archive_mode</> to <literal>on</> as well to enable archiving.
- The default autovacuum-related settings changed.
+ Previously <varname>archive_command</> controlled whether
+ archiving was performed. Now a new boolean configuration
+ parameter, <varname>archive_mode</>, controls this. Autovacuum's
+ default settings have changed.
</para>
</listitem>
Commenting out a parameter in <filename>postgresql.conf</> now
causes it to revert to its default value
</para>
+
+ <para>
+ Previously commenting out a value kept the value unchanged until
+ the next server restart.
+ </para>
</listitem>
<listitem>
<para>
- <literal>ARRAY(SELECT ...)</literal> now returns an empty array,
- rather than a NULL, when the sub-select returns zero rows
+ <literal>ARRAY(SELECT ...)</literal>, where <command>SELECT</>
+ returns no rows, now returns an empty array, rather than NULL
</para>
</listitem>
<listitem>
<para>
- <literal>ORDER BY ... USING</> <replaceable>operator</>
- will now be rejected if the <replaceable>operator</> is not a
- less-than or greater-than member of some btree operator class
+ <literal>ORDER BY ... USING</> <replaceable>operator</> now must
+ use a less-than or greater-than <replaceable>operator</> that is
+ defined in a btree operator class
</para>
<para>
- This prevents less-than-sane behavior that formerly ensued if an
- operator that doesn't actually define a proper sort ordering was
- specified.
+ This restriction was added to prevent unexpected results.
</para>
</listitem>
<listitem>
<para>
- The array type associated with a type named <quote>foo</quote>
- is not necessarily named <quote>_foo</quote> anymore
+ The array name for a base data type is no longer required to
+ be the data type name with an underscore prefix
</para>
<para>
The old naming convention is still honored when possible, but
- client code should migrate away from depending on it.
+ client code should no longer depending on it.
</para>
</listitem>
<listitem>
<para>
- By default, non-superuser database owners can now instantiate trusted
- procedural languages in their databases
+ Non-superuser database owners now have privileges to add trusted
+ procedural languages in their databases by default
</para>
<para>
While this is reasonably safe, some administrators may wish to
- revoke the privilege.
+ revoke the privilege. It is controlled by
+ <structname>pg_pltemplate</>.<structfield>tmpldbacreate</>.
</para>
</listitem>
<listitem>
<para>
- The effects of <command>SET LOCAL</command> now persist until
- the end of the current top transaction, unless rolled back
+ <command>SET LOCAL</command> changes now persist until
+ the end of the top-most transaction, unless rolled back
</para>
<para>
- In 8.0 through 8.2, <command>SET LOCAL</command>'s
- effects disappeared at subtransaction commit, leading to behavior
- that made little sense at the SQL level (one would not normally
- expect <command>RELEASE</> to do such a thing).
+ Previously <command>SET LOCAL</command>'s effects reverted
+ during subtransaction commit and <command>RELEASE</>.
</para>
</listitem>
<listitem>
<para>
- Commands that are disallowed in transaction blocks are now disallowed
- in multiple-statement query strings, too
+ Commands that are disallowed in transaction blocks are now also
+ disallowed in multiple-statement query strings
</para>
<para>
For example, <literal>BEGIN; DROP DATABASE; COMMIT</> will now be
- rejected even if submitted as a single Query message. This was always
- quite unsafe, but the <function>PreventTransactionChain</function>
- test failed to detect it.
+ rejected even if submitted as a single query message.
</para>
</listitem>
<listitem>
<para>
- Additional checks for invalidly-encoded multibyte strings
+ Add additional checks for invalidly-encoded multibyte strings
</para>
<para>
- Some cases that might formerly have allowed invalid data to
- enter the database will now be rejected. In particular, the
- <function>chr()</function> function changed behavior.
+ For example, <function>chr()</function> has additional checks.
</para>
</listitem>
<listitem>
<para>
- <function>convert()</function> family of functions changed behavior
+ <function>convert()</function> encoding has changed behavior
</para>
<para>
- Strings that are not in the database's native encoding are now
- represented as type <type>bytea</> rather than type <type>text</>.
+ <type>bytea</> is now used for strings that do not match the
+ server encoding, and <function>convert_from</> and
+ <function>convert_to</> have been added for consistency.
</para>
</listitem>
<listitem>
<para>
- Minor security restrictions added to database-size inquiry functions
- and some contrib functions
+ Restrict object size functions to users who have reasonable
+ permissions to view such information
+ </para>
+
+ <para>
+ For example, database size now requires <literal>CONNECT</>
+ permission, and tablespaces size requires <literal>CREATE</>
+ permission.
</para>
</listitem>
<listitem>
<para>
- C code that manipulates variable-length datums will need changes
+ New C macros for handling variable-length data values
</para>
<para>
- The new <function>SET_VARSIZE()</> macro <emphasis>must</> be used
- to set the length word of a generated datum. Also, it may be
- necessary to <quote>detoast</quote> input varlena datums in cases
- where no toasting could have happened before.
+ The new <function>SET_VARSIZE()</> macro <emphasis>must</> be
+ used to set the length of generated values. Also, it might be
+ necessary to expand (<quote>de-TOAST</quote>) input values in
+ additional places.
</para>
</listitem>
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