Revert "Allow on-line enabling and disabling of data checksums"

This reverts the backend sides of commit 1fde38b.
I have, at least for now, left the pg_verify_checksums tool in place, as
this tool can be very valuable without the rest of the patch as well,
and since it's a read-only tool that only runs when the cluster is down
it should be a lot safer.

Author: mhagander

doc/src/sgml/func.sgml

@@ -19566,71 +19566,6 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
 
   </sect2>
 
-  <sect2 id="functions-admin-checksum">
-   <title>Data Checksum Functions</title>
-
-   <para>
-    The functions shown in <xref linkend="functions-checksums-table" /> can
-    be used to enable or disable data checksums in a running cluster.
-    See <xref linkend="checksums" /> for details.
-   </para>
-
-   <table id="functions-checksums-table">
-    <title>Checksum <acronym>SQL</acronym> Functions</title>
-    <tgroup cols="3">
-     <thead>
-      <row>
-       <entry>Function</entry>
-       <entry>Return Type</entry>
-       <entry>Description</entry>
-      </row>
-     </thead>
-     <tbody>
-      <row>
-       <entry>
-        <indexterm>
-         <primary>pg_enable_data_checksums</primary>
-        </indexterm>
-        <literal><function>pg_enable_data_checksums(<optional><parameter>cost_delay</parameter> <type>int</type>, <parameter>cost_limit</parameter> <type>int</type></optional>)</function></literal>
-       </entry>
-       <entry>
-        void
-       </entry>
-       <entry>
-        <para>
-         Initiates data checksums for the cluster. This will switch the data checksums mode
-         to <literal>in progress</literal> and start a background worker that will process
-         all data in the database and enable checksums for it. When all data pages have had
-         checksums enabled, the cluster will automatically switch to checksums
-         <literal>on</literal>.
-        </para>
-        <para>
-         If <parameter>cost_delay</parameter> and <parameter>cost_limit</parameter> are
-         specified, the speed of the process is throttled using the same principles as
-         <link linkend="runtime-config-resource-vacuum-cost">Cost-based Vacuum Delay</link>.
-        </para>
-       </entry>
-      </row>
-      <row>
-       <entry>
-        <indexterm>
-         <primary>pg_disable_data_checksums</primary>
-        </indexterm>
-        <literal><function>pg_disable_data_checksums()</function></literal>
-       </entry>
-       <entry>
-        void
-       </entry>
-       <entry>
-        Disables data checksums for the cluster.
-       </entry>
-      </row>
-     </tbody>
-    </tgroup>
-   </table>
-
-  </sect2>
-
   <sect2 id="functions-admin-dbobject">
    <title>Database Object Management Functions</title>
 

doc/src/sgml/ref/initdb.sgml

@@ -214,9 +214,9 @@ PostgreSQL documentation
        <para>
         Use checksums on data pages to help detect corruption by the
         I/O system that would otherwise be silent. Enabling checksums
-        may incur a noticeable performance penalty. If set, checksums
-        are calculated for all objects, in all databases. See
-        <xref linkend="checksums" /> for details.
+        may incur a noticeable performance penalty. This option can only
+        be set during initialization, and cannot be changed later. If
+        set, checksums are calculated for all objects, in all databases.
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/reference.sgml

@@ -284,7 +284,6 @@
    &pgtestfsync;
    &pgtesttiming;
    &pgupgrade;
-   &pgVerifyChecksums;
    &pgwaldump;
    &postgres;
    &postmaster;

doc/src/sgml/wal.sgml

@@ -230,87 +230,6 @@
   </para>
  </sect1>
 
- <sect1 id="checksums">
-  <title>Data checksums</title>
-  <indexterm>
-   <primary>checksums</primary>
-  </indexterm>
-
-  <para>
-   Data pages are not checksum protected by default, but this can optionally be enabled for a cluster.
-   When enabled, each data page will be assigned a checksum that is updated when the page is
-   written and verified every time the page is read. Only data pages are protected by checksums,
-   internal data structures and temporary files are not.
-  </para>
-
-  <para>
-   Checksums are normally enabled when the cluster is initialized using
-   <link linkend="app-initdb-data-checksums"><application>initdb</application></link>. They
-   can also be enabled or disabled at runtime. In all cases, checksums are enabled or disabled
-   at the full cluster level, and cannot be specified individually for databases or tables.
-  </para>
-
-  <para>
-   The current state of checksums in the cluster can be verified by viewing the value
-   of the read-only configuration variable <xref linkend="guc-data-checksums" /> by
-   issuing the command <command>SHOW data_checksums</command>.
-  </para>
-
-  <para>
-   When attempting to recover from corrupt data it may be necessary to bypass the checksum
-   protection in order to recover data. To do this, temporarily set the configuration parameter
-   <xref linkend="guc-ignore-checksum-failure" />.
-  </para>
-
-  <sect2 id="checksums-enable-disable">
-   <title>On-line enabling of checksums</title>
-
-   <para>
-    Checksums can be enabled or disabled online, by calling the appropriate
-    <link linkend="functions-admin-checksum">functions</link>.
-    Disabling of checksums takes effect immediately when the function is called.
-   </para>
-
-   <para>
-    Enabling checksums will put the cluster in <literal>inprogress</literal> mode.
-    During this time, checksums will be written but not verified. In addition to
-    this, a background worker process is started that enables checksums on all
-    existing data in the cluster. Once this worker has completed processing all
-    databases in the cluster, the checksum mode will automatically switch to
-    <literal>on</literal>.
-   </para>
-
-   <para>
-    The process will initially wait for all open transactions to finish before
-    it starts, so that it can be certain that there are no tables that have been
-    created inside a transaction that has not committed yet and thus would not
-    be visible to the process enabling checksums. It will also, for each database,
-    wait for all pre-existing temporary tables to get removed before it finishes.
-    If long-lived temporary tables are used in the application it may be necessary
-    to terminate these application connections to allow the process to complete.
-    Information about open transactions and connections with temporary tables is
-    written to log.
-   </para>
-
-   <para>
-    If the cluster is stopped while in <literal>inprogress</literal> mode, for
-    any reason, then this process must be restarted manually. To do this,
-    re-execute the function <function>pg_enable_data_checksums()</function>
-    once the cluster has been restarted. It is not possible to resume the work,
-    the process has to start over and re-process the cluster.
-   </para>
-
-   <note>
-    <para>
-     Enabling checksums can cause significant I/O to the system, as most of the
-     database pages will need to be rewritten, and will be written both to the
-     data files and the WAL.
-    </para>
-   </note>
-
-  </sect2>
- </sect1>
-
   <sect1 id="wal-intro">
    <title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
 

src/backend/access/rmgrdesc/xlogdesc.c

@@ -17,7 +17,6 @@
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "catalog/pg_control.h"
-#include "storage/bufpage.h"
 #include "utils/guc.h"
 #include "utils/timestamp.h"
 
@@ -138,18 +137,6 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 						 xlrec.ThisTimeLineID, xlrec.PrevTimeLineID,
 						 timestamptz_to_str(xlrec.end_time));
 	}
-	else if (info == XLOG_CHECKSUMS)
-	{
-		xl_checksum_state xlrec;
-
-		memcpy(&xlrec, rec, sizeof(xl_checksum_state));
-		if (xlrec.new_checksumtype == PG_DATA_CHECKSUM_VERSION)
-			appendStringInfo(buf, "on");
-		else if (xlrec.new_checksumtype == PG_DATA_CHECKSUM_INPROGRESS_VERSION)
-			appendStringInfo(buf, "inprogress");
-		else
-			appendStringInfo(buf, "off");
-	}
 }
 
 const char *
@@ -195,9 +182,6 @@ xlog_identify(uint8 info)
 		case XLOG_FPI_FOR_HINT:
 			id = "FPI_FOR_HINT";
 			break;
-		case XLOG_CHECKSUMS:
-			id = "CHECKSUMS";
-			break;
 	}
 
 	return id;

src/backend/access/transam/xlog.c

@@ -856,7 +856,6 @@ static void SetLatestXTime(TimestampTz xtime);
 static void SetCurrentChunkStartTime(TimestampTz xtime);
 static void CheckRequiredParameterValues(void);
 static void XLogReportParameters(void);
-static void XlogChecksums(ChecksumType new_type);
 static void checkTimeLineSwitch(XLogRecPtr lsn, TimeLineID newTLI,
 					TimeLineID prevTLI);
 static void LocalSetXLogInsertAllowed(void);
@@ -1034,7 +1033,7 @@ XLogInsertRecord(XLogRecData *rdata,
 		Assert(RedoRecPtr < Insert->RedoRecPtr);
 		RedoRecPtr = Insert->RedoRecPtr;
 	}
-	doPageWrites = (Insert->fullPageWrites || Insert->forcePageWrites || DataChecksumsInProgress());
+	doPageWrites = (Insert->fullPageWrites || Insert->forcePageWrites);
 
 	if (fpw_lsn != InvalidXLogRecPtr && fpw_lsn <= RedoRecPtr && doPageWrites)
 	{
@@ -4674,6 +4673,10 @@ ReadControlFile(void)
 		(SizeOfXLogLongPHD - SizeOfXLogShortPHD);
 
 	CalculateCheckpointSegments();
+
+	/* Make the initdb settings visible as GUC variables, too */
+	SetConfigOption("data_checksums", DataChecksumsEnabled() ? "yes" : "no",
+					PGC_INTERNAL, PGC_S_OVERRIDE);
 }
 
 void
@@ -4745,90 +4748,12 @@ GetMockAuthenticationNonce(void)
  * Are checksums enabled for data pages?
  */
 bool
-DataChecksumsNeedWrite(void)
+DataChecksumsEnabled(void)
 {
 	Assert(ControlFile != NULL);
 	return (ControlFile->data_checksum_version > 0);
 }
 
-bool
-DataChecksumsNeedVerify(void)
-{
-	Assert(ControlFile != NULL);
-
-	/*
-	 * Only verify checksums if they are fully enabled in the cluster. In
-	 * inprogress state they are only updated, not verified.
-	 */
-	return (ControlFile->data_checksum_version == PG_DATA_CHECKSUM_VERSION);
-}
-
-bool
-DataChecksumsInProgress(void)
-{
-	Assert(ControlFile != NULL);
-	return (ControlFile->data_checksum_version == PG_DATA_CHECKSUM_INPROGRESS_VERSION);
-}
-
-void
-SetDataChecksumsInProgress(void)
-{
-	Assert(ControlFile != NULL);
-	if (ControlFile->data_checksum_version > 0)
-		return;
-
-	XlogChecksums(PG_DATA_CHECKSUM_INPROGRESS_VERSION);
-
-	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
-	ControlFile->data_checksum_version = PG_DATA_CHECKSUM_INPROGRESS_VERSION;
-	UpdateControlFile();
-	LWLockRelease(ControlFileLock);
-}
-
-void
-SetDataChecksumsOn(void)
-{
-	Assert(ControlFile != NULL);
-
-	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
-
-	if (ControlFile->data_checksum_version != PG_DATA_CHECKSUM_INPROGRESS_VERSION)
-	{
-		LWLockRelease(ControlFileLock);
-		elog(ERROR, "Checksums not in inprogress mode");
-	}
-
-	ControlFile->data_checksum_version = PG_DATA_CHECKSUM_VERSION;
-	UpdateControlFile();
-	LWLockRelease(ControlFileLock);
-
-	XlogChecksums(PG_DATA_CHECKSUM_VERSION);
-}
-
-void
-SetDataChecksumsOff(void)
-{
-	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
-
-	ControlFile->data_checksum_version = 0;
-	UpdateControlFile();
-	LWLockRelease(ControlFileLock);
-
-	XlogChecksums(0);
-}
-
-/* guc hook */
-const char *
-show_data_checksums(void)
-{
-	if (ControlFile->data_checksum_version == PG_DATA_CHECKSUM_VERSION)
-		return "on";
-	else if (ControlFile->data_checksum_version == PG_DATA_CHECKSUM_INPROGRESS_VERSION)
-		return "inprogress";
-	else
-		return "off";
-}
-
 /*
  * Returns a fake LSN for unlogged relations.
  *
@@ -7863,16 +7788,6 @@ StartupXLOG(void)
 	 */
 	CompleteCommitTsInitialization();
 
-	/*
-	 * If we reach this point with checksums in inprogress state, we notify
-	 * the user that they need to manually restart the process to enable
-	 * checksums.
-	 */
-	if (ControlFile->data_checksum_version == PG_DATA_CHECKSUM_INPROGRESS_VERSION)
-		ereport(WARNING,
-				(errmsg("checksum state is \"inprogress\" with no worker"),
-				 errhint("Either disable or enable checksums by calling the pg_disable_data_checksums() or pg_enable_data_checksums() functions.")));
-
 	/*
 	 * All done with end-of-recovery actions.
 	 *
@@ -9626,22 +9541,6 @@ XLogReportParameters(void)
 	}
 }
 
-/*
- * Log the new state of checksums
- */
-static void
-XlogChecksums(ChecksumType new_type)
-{
-	xl_checksum_state xlrec;
-
-	xlrec.new_checksumtype = new_type;
-
-	XLogBeginInsert();
-	XLogRegisterData((char *) &xlrec, sizeof(xl_checksum_state));
-
-	XLogInsert(RM_XLOG_ID, XLOG_CHECKSUMS);
-}
-
 /*
  * Update full_page_writes in shared memory, and write an
  * XLOG_FPW_CHANGE record if necessary.
@@ -10070,17 +9969,6 @@ xlog_redo(XLogReaderState *record)
 		/* Keep track of full_page_writes */
 		lastFullPageWrites = fpw;
 	}
-	else if (info == XLOG_CHECKSUMS)
-	{
-		xl_checksum_state state;
-
-		memcpy(&state, XLogRecGetData(record), sizeof(xl_checksum_state));
-
-		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
-		ControlFile->data_checksum_version = state.new_checksumtype;
-		UpdateControlFile();
-		LWLockRelease(ControlFileLock);
-	}
 }
 
 #ifdef WAL_DEBUG