Allow I/O reliability checks using 16-bit checksums

Checksums are set immediately prior to flush out of shared buffers
and checked when pages are read in again. Hint bit setting will
require full page write when block is dirtied, which causes various
infrastructure changes. Extensive comments, docs and README.

WARNING message thrown if checksum fails on non-all zeroes page;
ERROR thrown but can be disabled with ignore_checksum_failure = on.

Feature enabled by an initdb option, since transition from option off
to option on is long and complex and has not yet been implemented.
Default is not to use checksums.

Checksum used is WAL CRC-32 truncated to 16-bits.

Simon Riggs, Jeff Davis, Greg Smith
Wide input and assistance from many community members. Thank you.

1 files changed, 14 insertions, 0 deletions

diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index a1e46eb4c67..b1067e23505 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -182,6 +182,20 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry id="app-initdb-data-checksums" xreflabel="data checksums">
+      <term><option>-k</option></term>
+      <term><option>--data-checksums</option></term>
+      <listitem>
+       <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.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>--locale=<replaceable>locale</replaceable></option></term>
       <listitem>