Add GUC full_page_writes to control writing full pages to WAL.
This commit is contained in:
Bruce Momjian
parent
c19aa704c8
commit
326a7a0788
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.335 2005/07/02 19:16:36 momjian Exp $
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$PostgreSQL: pgsql/doc/src/sgml/runtime.sgml,v 1.336 2005/07/05 23:18:09 momjian Exp $
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-->
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<chapter Id="runtime">
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@ -1660,7 +1660,9 @@ SET ENABLE_SEQSCAN TO OFF;
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<para>
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This option can only be set at server start or in the
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<filename>postgresql.conf</filename> file.
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<filename>postgresql.conf</filename> file. If this option
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is <literal>off</>, consider also turning off
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<varname>guc-full-page-writes</>.
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</para>
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</listitem>
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</varlistentry>
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@ -1687,6 +1689,37 @@ SET ENABLE_SEQSCAN TO OFF;
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</listitem>
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</varlistentry>
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<varlistentry id="guc-full-page-writes" xreflabel="full_page_writes">
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<indexterm>
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<primary><varname>full_page_writes</> configuration parameter</primary>
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</indexterm>
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<term><varname>full_page_writes</varname> (<type>boolean</type>)</term>
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<listitem>
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<para>
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A page write in process during an operating system crash might
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be only partially written to disk, leading to an on-disk page
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that contains a mix of old and new data. During recovery, the
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row changes stored in WAL are not enough to completely restore
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the page.
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</para>
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<para>
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When this option is on, the <productname>PostgreSQL</> server
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writes full pages to WAL when they first modified after a checkpoint
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so full recovery is possible. Turning this option off might lead
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to a corrupt system after an operating system crash because
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uncorrected partial pages might contain inconsistent or corrupt
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data. The risks are less but similar to <varname>fsync</>.
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</para>
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<para>
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This option can only be set at server start or in the
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<filename>postgresql.conf</filename> file. The default is
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<literal>on</>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="guc-wal-buffers" xreflabel="wal_buffers">
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<term><varname>wal_buffers</varname> (<type>integer</type>)</term>
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<indexterm>
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.206 2005/07/04 04:51:44 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.207 2005/07/05 23:18:09 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -103,6 +103,7 @@ int XLOGbuffers = 8;
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char *XLogArchiveCommand = NULL;
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char *XLOG_sync_method = NULL;
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const char XLOG_sync_method_default[] = DEFAULT_SYNC_METHOD_STR;
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bool fullPageWrites = true;
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#ifdef WAL_DEBUG
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bool XLOG_DEBUG = false;
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@ -594,7 +595,9 @@ begin:;
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{
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/* OK, put it in this slot */
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dtbuf[i] = rdt->buffer;
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if (XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
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/* If fsync is off, no need to backup pages. */
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if (fullPageWrites &&
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XLogCheckBuffer(rdt, &(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
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{
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dtbuf_bkp[i] = true;
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rdt->data = NULL;
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@ -10,7 +10,7 @@
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* Written by Peter Eisentraut <peter_e@gmx.net>.
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.272 2005/07/04 04:51:51 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.273 2005/07/05 23:18:10 momjian Exp $
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*
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*--------------------------------------------------------------------
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*/
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@ -83,6 +83,7 @@ extern DLLIMPORT bool check_function_bodies;
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extern int CommitDelay;
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extern int CommitSiblings;
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extern char *default_tablespace;
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extern bool fullPageWrites;
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static const char *assign_log_destination(const char *value,
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bool doit, GucSource source);
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@ -482,6 +483,18 @@ static struct config_bool ConfigureNamesBool[] =
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&zero_damaged_pages,
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false, NULL, NULL
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},
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{
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{"full_page_writes", PGC_SIGHUP, WAL_SETTINGS,
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gettext_noop("Writes full pages to WAL when first modified after a checkpoint."),
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gettext_noop("A page write in process during an operating system crash might be "
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"only partially written to disk. During recovery, the row changes"
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"stored in WAL are not enough to recover. This option writes "
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"pages when first modified after a checkpoint to WAL so full recovery "
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"is possible.")
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},
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&fullPageWrites,
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true, NULL, NULL
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},
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{
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{"silent_mode", PGC_POSTMASTER, LOGGING_WHEN,
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gettext_noop("Runs the server silently."),
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@ -121,6 +121,7 @@
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#wal_sync_method = fsync # the default varies across platforms:
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# fsync, fdatasync, fsync_writethrough,
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# open_sync, open_datasync
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#full_page_writes = on # recover from partial page writes
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#wal_buffers = 8 # min 4, 8KB each
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#commit_delay = 0 # range 0-100000, in microseconds
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#commit_siblings = 5 # range 1-1000
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