Introduce wal_level GUC to explicitly control if information needed for

archival or hot standby should be WAL-logged, instead of deducing that from
other options like archive_mode. This replaces recovery_connections GUC in
the primary, where it now has no effect, but it's still used in the standby
to enable/disable hot standby.

Remove the WAL-logging of "unlogged operations", like creating an index
without WAL-logging and fsyncing it at the end. Instead, we keep a copy of
the wal_mode setting and the settings that affect how much shared memory a
hot standby server needs to track master transactions (max_connections,
max_prepared_xacts, max_locks_per_xact) in pg_control. Whenever the settings
change, at server restart, write a WAL record noting the new settings and
update pg_control. This allows us to notice the change in those settings in
the standby at the right moment, they used to be included in checkpoint
records, but that meant that a changed value was not reflected in the
standby until the first checkpoint after the change.

Bump PG_CONTROL_VERSION and XLOG_PAGE_MAGIC. Whack XLOG_PAGE_MAGIC back to
the sequence it used to follow, before hot standby and subsequent patches
changed it to 0x9003.

4 files changed, 79 insertions, 43 deletions

diff --git a/doc/src/sgml/backup.sgml b/doc/src/sgml/backup.sgml
index 3c5e0d5a8ec..9055517af54 100644
--- a/doc/src/sgml/backup.sgml
+++ b/doc/src/sgml/backup.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.152 2010/04/20 00:26:06 rhaas Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/backup.sgml,v 2.153 2010/04/28 16:10:39 heikki Exp $ -->
 
 <chapter id="backup">
  <title>Backup and Restore</title>
@@ -689,8 +689,7 @@ archive_command = 'test ! -f /mnt/server/archivedir/%f &amp;&amp; cp %p /mnt/ser
    </para>
 
    <para>
-    When <varname>archive_mode</> is <literal>off</> and <xref
-    linkend="guc-max-wal-senders"> is zero some SQL commands
+    When <varname>wal_level</> is <literal>minimal</> some SQL commands
     are optimized to avoid WAL logging, as described in <xref
     linkend="populate-pitr">.  If archiving or streaming replication were
     turned on during execution of one of these statements, WAL would not
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 71bab707da8..93c9ff183c2 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.270 2010/04/26 10:51:59 rhaas Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.271 2010/04/28 16:10:39 heikki Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -1353,6 +1353,45 @@ SET ENABLE_SEQSCAN TO OFF;
      <title>Settings</title>
      <variablelist>
      
+     <varlistentry id="guc-wal-level" xreflabel="wal_level">
+      <term><varname>wal_level</varname> (<type>enum</type>)</term>
+      <indexterm>
+       <primary><varname>wal_level</> configuration parameter</primary>
+      </indexterm>
+      <listitem>
+       <para>
+        <varname>wal_level</> determines how much information is written
+        to the WAL. The default value is <literal>minimal</>, which writes
+        only minimal information needed to recover from a crash or immediate
+        shutdown. <literal>archive</> adds logging required for WAL archiving,
+        and <literal>hot_standby</> further adds information required to run
+        read-only queries on a standby server.
+        This parameter can only be set at server start.
+       </para>
+       <para>
+        In <literal>minimal</> level, WAL-logging of some bulk operations, like
+        <command>CREATE INDEX</>, <command>CLUSTER</> and <command>COPY</> on
+        a table that was created or truncated in the same transaction can be
+        safely skipped, which can make those operations much faster (see
+        <xref linkend="populate-pitr">). But minimal WAL does not contain
+        enough information to reconstruct the data from a base backup and the
+        WAL logs, so at least <literal>archive</> level must be used to enable
+        WAL archiving (<xref linkend="guc-archive-mode">) and streaming
+        replication.
+       </para>
+       <para>
+        In <literal>hot_standby</> level, the same information is logged as
+        with <literal>archive</>, plus information needed to reconstruct
+        the status of running transactions from the WAL. To enable read-only
+        queries on a standby server, <varname>wal_level</> must be set to
+        <literal>hot_standby</> on the primary. It is thought that there is
+        little measurable difference in performance from using
+        <literal>hot_standby</> level over <literal>archive</>, so feedback
+        is welcome if any production impacts are noticeable.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-fsync" xreflabel="fsync">
       <indexterm>
        <primary><varname>fsync</> configuration parameter</primary>
@@ -1726,7 +1765,9 @@ SET ENABLE_SEQSCAN TO OFF;
         <varname>archive_mode</> and <varname>archive_command</> are
         separate variables so that <varname>archive_command</> can be
         changed without leaving archiving mode.
-        This parameter can only be set at server start.
+        This parameter can only be set at server start. <varname>wal_level</>
+        must be set to <literal>archive</> or <literal>hot_standby</> to
+        enable <varname>archive_mode</>.
        </para>
       </listitem>
      </varlistentry>
@@ -1818,7 +1859,9 @@ SET ENABLE_SEQSCAN TO OFF;
         Specifies the maximum number of concurrent connections from standby
         servers (i.e., the maximum number of simultaneously running WAL sender
         processes). The default is zero. This parameter can only be set at
-        server start.
+        server start. <varname>wal_level</> must be set to <literal>archive</>
+        or <literal>hot_standby</> to allow connections from standby
+        connections.
        </para>
        </listitem>
       </varlistentry>
@@ -1884,16 +1927,11 @@ SET ENABLE_SEQSCAN TO OFF;
       </indexterm>
       <listitem>
        <para>
-        Parameter has two roles. During recovery, specifies whether or not
-        you can connect and run queries to enable <xref linkend="hot-standby">.
-        During normal running, specifies whether additional information is written
-        to WAL to allow recovery connections on a standby server that reads
-        WAL data generated by this server. The default value is
-        <literal>on</literal>.  It is thought that there is little
-        measurable difference in performance from using this feature, so
-        feedback is welcome if any production impacts are noticeable.
-        It is likely that this parameter will be removed in later releases.
-        This parameter can only be set at server start.
+        Specifies whether or not you can connect and run queries during
+        recovery, for <xref linkend="hot-standby">. The default value is
+        <literal>on</literal>.
+        This parameter can only be set at server start. It only has effect
+        during archive recovery or in standby mode.
        </para>
       </listitem>
      </varlistentry>
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index 463bac1f480..da0d4d5de5f 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.63 2010/04/26 19:09:25 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/high-availability.sgml,v 1.64 2010/04/28 16:10:40 heikki Exp $ -->
 
 <chapter id="high-availability">
  <title>High Availability, Load Balancing, and Replication</title>
@@ -1593,9 +1593,9 @@ LOG:  database system is ready to accept read only connections
 </programlisting>
 
     Consistency information is recorded once per checkpoint on the primary, as long
-    as <varname>recovery_connections</> is enabled on the primary.  It is not possible
+    as <varname>wal_level</> is set to <literal>hot_standby</> on the primary.  It is not possible
     to enable recovery connections on the standby when reading WAL written during the
-    period that <varname>recovery_connections</> was disabled on the primary.
+    period that <varname>wal_level</> was not set to <literal>hot_standby</> on the primary.
     Reaching a consistent state can also be delayed in the presence
     of both of these conditions:
 
@@ -1842,7 +1842,7 @@ LOG:  database system is ready to accept read only connections
    </para>
 
    <para>
-    On the primary, parameters <varname>recovery_connections</> and
+    On the primary, parameters <varname>wal_level</> and
     <varname>vacuum_defer_cleanup_age</> can be used.
     <varname>max_standby_delay</> has no effect if set on the primary.
    </para>
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index ccccb3fefb0..bd93cb0dd2e 100644
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.76 2010/04/20 00:26:06 rhaas Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.77 2010/04/28 16:10:40 heikki Exp $ -->
 
  <chapter id="performance-tips">
   <title>Performance Tips</title>
@@ -835,10 +835,9 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
     <command>TRUNCATE</command> command. In such cases no WAL
     needs to be written, because in case of an error, the files
     containing the newly loaded data will be removed anyway.
-    However, this consideration does not apply when
-    <xref linkend="guc-archive-mode"> is on or streaming replication
-    is allowed (i.e., <xref linkend="guc-max-wal-senders"> is more
-    than or equal to one), as all commands must write WAL in that case.
+    However, this consideration only applies when
+    <xref linkend="guc-wal-level"> is <literal>minimal</> as all commands
+    must write WAL otherwise.
    </para>
 
   </sect2>
@@ -910,29 +909,27 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
   </sect2>
 
   <sect2 id="populate-pitr">
-   <title>Turn off <varname>archive_mode</varname> and streaming replication</title>
+   <title>Disable WAL archival and streaming replication</title>
 
    <para>
     When loading large amounts of data into an installation that uses
-    WAL archiving or streaming replication, you might want to disable
-    archiving (turn off the <xref linkend="guc-archive-mode">
-    configuration variable) and replication (zero the
-    <xref linkend="guc-max-wal-senders"> configuration variable)
-    while loading.  It might be
-    faster to take a new base backup after the load has completed
-    than to process a large amount of incremental WAL data.
-    But note that changing either of these variables requires
-    a server restart.
+    WAL archiving or streaming replication, it might be faster to take a
+    new base backup after the load has completed than to process a large
+    amount of incremental WAL data. You might want to disable archiving
+    and streaming replication while loading, by setting
+    <xref linkend="guc-wal-level"> to <literal>minimal</>,
+    <xref linkend="guc-archive-mode"> <literal>off</>, and
+    <xref linkend="guc-max-wal-senders"> to zero).
+    But note that changing these settings requires a server restart.
    </para>
 
    <para>
     Aside from avoiding the time for the archiver or WAL sender to
     process the WAL data,
     doing this will actually make certain commands faster, because they
-    are designed not to write WAL at all if <varname>archive_mode</varname>
-    is off and <varname>max_wal_senders</varname> is zero.  (They can
-    guarantee crash safety more cheaply by doing an
-    <function>fsync</> at the end than by writing WAL.)
+    are designed not to write WAL at all if <varname>wal_level</varname>
+    is <literal>minimal</>.  (They can guarantee crash safety more cheaply
+    by doing an <function>fsync</> at the end than by writing WAL.)
     This applies to the following commands:
     <itemizedlist>
      <listitem>
@@ -1014,10 +1011,12 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
      </listitem>
      <listitem>
       <para>
-       If using WAL archiving, consider disabling it during the restore.
-       To do that, turn off <varname>archive_mode</varname> before loading the
-       dump script, and afterwards turn it back on
-       and take a fresh base backup.
+       If using WAL archiving or streaming replication, consider disabling
+       them during the restore. To do that, set <varname>arcive_mode</> off,
+       <varname>wal_level</varname> to <literal>minimal</>, and
+       <varname>max_wal_senders</> zero before loading the dump script,
+       and afterwards set them back to the right values and take a fresh
+       base backup.
       </para>
      </listitem>
      <listitem>