Allow on-line enabling and disabling of data checksums

This makes it possible to turn checksums on in a live cluster, without
the previous need for dump/reload or logical replication (and to turn it
off).

Enabling checkusm starts a background process in the form of a
launcher/worker combination that goes through the entire database and
recalculates checksums on each and every page. Only when all pages have
been checksummed are they fully enabled in the cluster. Any failure of
the process will revert to checksums off and the process has to be
started.

This adds a new WAL record that indicates the state of checksums, so
the process works across replicated clusters.

Authors: Magnus Hagander and Daniel Gustafsson
Review: Tomas Vondra, Michael Banck, Heikki Linnakangas, Andrey Borodin

3 files changed, 116 insertions, 3 deletions

diff --git a/doc/src/sgml/ref/allfiles.sgml b/doc/src/sgml/ref/allfiles.sgml
index 4e01e5641cf..7cd6ee85dc9 100644
--- a/doc/src/sgml/ref/allfiles.sgml
+++ b/doc/src/sgml/ref/allfiles.sgml
@@ -211,6 +211,7 @@ Complete list of usable sgml source files in this directory.
 <!ENTITY pgResetwal         SYSTEM "pg_resetwal.sgml">
 <!ENTITY pgRestore          SYSTEM "pg_restore.sgml">
 <!ENTITY pgRewind           SYSTEM "pg_rewind.sgml">
+<!ENTITY pgVerifyChecksums  SYSTEM "pg_verify_checksums.sgml">
 <!ENTITY pgtestfsync        SYSTEM "pgtestfsync.sgml">
 <!ENTITY pgtesttiming       SYSTEM "pgtesttiming.sgml">
 <!ENTITY pgupgrade          SYSTEM "pgupgrade.sgml">
diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index 949b5a220f5..826dd91f729 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -195,9 +195,9 @@ 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. This option can only
-        be set during initialization, and cannot be changed later. If
-        set, checksums are calculated for all objects, in all databases.
+        may incur a noticeable performance penalty. If set, checksums
+        are calculated for all objects, in all databases. See
+        <xref linkend="checksums" /> for details.
        </para>
       </listitem>
      </varlistentry>
diff --git a/doc/src/sgml/ref/pg_verify_checksums.sgml b/doc/src/sgml/ref/pg_verify_checksums.sgml
new file mode 100644
index 00000000000..463ecd5e1b3
--- /dev/null
+++ b/doc/src/sgml/ref/pg_verify_checksums.sgml
@@ -0,0 +1,112 @@
+<!--
+doc/src/sgml/ref/pg_verify_checksums.sgml
+PostgreSQL documentation
+-->
+
+<refentry id="pgverifychecksums">
+ <indexterm zone="pgverifychecksums">
+  <primary>pg_verify_checksums</primary>
+ </indexterm>
+
+ <refmeta>
+  <refentrytitle><application>pg_verify_checksums</application></refentrytitle>
+  <manvolnum>1</manvolnum>
+  <refmiscinfo>Application</refmiscinfo>
+ </refmeta>
+
+ <refnamediv>
+  <refname>pg_verify_checksums</refname>
+  <refpurpose>verify data checksums in an offline <productname>PostgreSQL</productname> database cluster</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+  <cmdsynopsis>
+   <command>pg_verify_checksums</command>
+   <arg choice="opt"><replaceable class="parameter">option</replaceable></arg>
+   <arg choice="opt"><arg choice="opt"><option>-D</option></arg> <replaceable class="parameter">datadir</replaceable></arg>
+  </cmdsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1 id="r1-app-pg_verify_checksums-1">
+  <title>Description</title>
+  <para>
+   <command>pg_verify_checksums</command> verifies data checksums in a PostgreSQL
+   cluster. It must be run against a cluster that's offline.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Options</title>
+
+   <para>
+    The following command-line options are available:
+
+    <variablelist>
+
+     <varlistentry>
+      <term><option>-r <replaceable>relfilenode</replaceable></option></term>
+      <listitem>
+       <para>
+        Only validate checksums in the relation with specified relfilenode.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><option>-f</option></term>
+      <listitem>
+       <para>
+        Force check even if checksums are disabled on cluster.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><option>-d</option></term>
+      <listitem>
+       <para>
+        Enable debug output. Lists all checked blocks and their checksum.
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
+       <term><option>-V</option></term>
+       <term><option>--version</option></term>
+       <listitem>
+       <para>
+       Print the <application>pg_verify_checksums</application> version and exit.
+       </para>
+       </listitem>
+     </varlistentry>
+
+     <varlistentry>
+      <term><option>-?</option></term>
+      <term><option>--help</option></term>
+       <listitem>
+        <para>
+         Show help about <application>pg_verify_checksums</application> command line
+         arguments, and exit.
+        </para>
+       </listitem>
+      </varlistentry>
+    </variablelist>
+   </para>
+ </refsect1>
+
+ <refsect1>
+  <title>Notes</title>
+  <para>
+    Can only be run when the server is offline.
+  </para>
+ </refsect1>
+
+ <refsect1>
+  <title>See Also</title>
+
+  <simplelist type="inline">
+   <member><xref linkend="checksums"/></member>
+  </simplelist>
+ </refsect1>
+
+</refentry>