Add GUC full_page_writes to control writing full pages to WAL.

diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 6b45299a16dbc40129eb2c64dd1a59f12459ccd4..3c683210d4b414585efbd27543e3e9dc3f577506 100644 (file)
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.335 2005/07/02 19:16:36 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.336 2005/07/05 23:18:09 momjian Exp $
 -->
 
 <chapter Id="runtime">
@@ -1660,7 +1660,9 @@ SET ENABLE_SEQSCAN TO OFF;
 
        <para>
         This option can only be set at server start or in the
-        <filename>postgresql.conf</filename> file.
+        <filename>postgresql.conf</filename> file.  If this option
+        is <literal>off</>, consider also turning off 
+        <varname>guc-full-page-writes</>.
        </para>
       </listitem>
      </varlistentry>
@@ -1687,6 +1689,37 @@ SET ENABLE_SEQSCAN TO OFF;
       </listitem>
      </varlistentry>
      
+     <varlistentry id="guc-full-page-writes" xreflabel="full_page_writes">
+      <indexterm>
+       <primary><varname>full_page_writes</> configuration parameter</primary>
+      </indexterm>
+      <term><varname>full_page_writes</varname> (<type>boolean</type>)</term>
+      <listitem>
+       <para>
+        A page write in process during an operating system crash might
+        be only partially written to disk, leading to an on-disk page
+        that contains a mix of old and new data. During recovery, the
+        row changes stored in WAL are not enough to completely restore
+        the page.
+       </para>
+
+       <para>
+        When this option is on, the <productname>PostgreSQL</> server
+        writes full pages to WAL when they first modified after a checkpoint
+        so full recovery is possible. Turning this option off might lead
+        to a corrupt system after an operating system crash because
+        uncorrected partial pages might contain inconsistent or corrupt
+        data. The risks are less but similar to <varname>fsync</>.
+       </para>
+
+       <para>
+        This option can only be set at server start or in the
+        <filename>postgresql.conf</filename> file.  The default is
+        <literal>on</>.
+       </para>
+      </listitem>
+     </varlistentry>
+     
      <varlistentry id="guc-wal-buffers" xreflabel="wal_buffers">
       <term><varname>wal_buffers</varname> (<type>integer</type>)</term>
       <indexterm>

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index d42aa93c547318e0690bbe0743df325803bf707e..86e1e6878b8dcb62d39e163fa49a1a008660258f 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.206 2005/07/04 04:51:44 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.207 2005/07/05 23:18:09 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -103,6 +103,7 @@ int                 XLOGbuffers = 8;
 char      *XLogArchiveCommand = NULL;
 char      *XLOG_sync_method = NULL;
 const char     XLOG_sync_method_default[] = DEFAULT_SYNC_METHOD_STR;
+bool           fullPageWrites = true;
 
 #ifdef WAL_DEBUG
 bool           XLOG_DEBUG = false;
@@ -594,7 +595,9 @@ begin:;
                                {
                                        /* OK, put it in this slot */
                                        dtbuf[i] = rdt->buffer;
-                                       if (XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
+                                       /* If fsync is off, no need to backup pages. */
+                                       if (fullPageWrites &&
+                                               XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
                                        {
                                                dtbuf_bkp[i] = true;
                                                rdt->data = NULL;

diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0ea335770c330552164b3e112cda41ddcef780cf..ca59f6755b4d8f3966acbcdafd1a8583d2d00088 100644 (file)
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -10,7 +10,7 @@
  * Written by Peter Eisentraut <peter_e@gmx.net>.
  *
  * IDENTIFICATION
- *       $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.272 2005/07/04 04:51:51 tgl Exp $
+ *       $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.273 2005/07/05 23:18:10 momjian Exp $
  *
  *--------------------------------------------------------------------
  */
@@ -83,6 +83,7 @@ extern DLLIMPORT bool check_function_bodies;
 extern int     CommitDelay;
 extern int     CommitSiblings;
 extern char *default_tablespace;
+extern bool    fullPageWrites;
 
 static const char *assign_log_destination(const char *value,
                                           bool doit, GucSource source);
@@ -482,6 +483,18 @@ static struct config_bool ConfigureNamesBool[] =
                &zero_damaged_pages,
                false, NULL, NULL
        },
+       {
+               {"full_page_writes", PGC_SIGHUP, WAL_SETTINGS,
+                       gettext_noop("Writes full pages to WAL when first modified after a checkpoint."),
+                       gettext_noop("A page write in process during an operating system crash might be "
+                                                "only partially written to disk.  During recovery, the row changes"
+                                                "stored in WAL are not enough to recover.  This option writes "
+                                                "pages when first modified after a checkpoint to WAL so full recovery "
+                                                "is possible.")
+               },
+               &fullPageWrites,
+               true, NULL, NULL
+       },
        {
                {"silent_mode", PGC_POSTMASTER, LOGGING_WHEN,
                        gettext_noop("Runs the server silently."),

diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 4e7c9207ddc130b57c7a5c357e9872d0a2023dca..193b0303b38c070d7cd5224df094431067a579db 100644 (file)
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -121,6 +121,7 @@
 #wal_sync_method = fsync       # the default varies across platforms:
                                # fsync, fdatasync, fsync_writethrough,
                                # open_sync, open_datasync
+#full_page_writes = on         # recover from partial page writes
 #wal_buffers = 8               # min 4, 8KB each
 #commit_delay = 0              # range 0-100000, in microseconds
 #commit_siblings = 5           # range 1-1000