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Allow I/O reliability checks using 16-bit checksums

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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.
This commit is contained in:
Simon Riggs
2013-03-22 13:54:07 +00:00
parent e4a05c7512
commit 96ef3b8ff1
40 changed files with 766 additions and 146 deletions
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24
doc/src/sgml/config.sgml
View File

@ -6629,6 +6629,30 @@ LOG: CleanUpLock: deleting: lock(0xb7acd844) id(24688,24696,0,0,0,1)
</listitem>
</varlistentry>
<varlistentry id="guc-ignore-checksum-failure" xreflabel="ignore_checksum_failure">
<term><varname>ignore_checksum_failure</varname> (<type>boolean</type>)</term>
<indexterm>
<primary><varname>ignore_checksum_failure</> configuration parameter</primary>
</indexterm>
<listitem>
<para>
Only has effect if <xref linkend="app-initdb-data-checksums"> are enabled.
</para>
<para>
Detection of a checksum failure during a read normally causes
<productname>PostgreSQL</> to report an error, aborting the current
transaction. Setting <varname>ignore_checksum_failure</> to on causes
the system to ignore the failure (but still report a warning), and
continue processing. This behavior may <emphasis>cause crashes, propagate
or hide corruption, or other serious problems</>. However, it may allow
you to get past the error and retrieve undamaged tuples that might still be
present in the table if the block header is still sane. If the header is
corrupt an error will be reported even if this option is enabled. The
default setting is <literal>off</>, and it can only be changed by a superuser.
</para>
</listitem>
</varlistentry>
<varlistentry id="guc-zero-damaged-pages" xreflabel="zero_damaged_pages">
<term><varname>zero_damaged_pages</varname> (<type>boolean</type>)</term>
<indexterm>

14
doc/src/sgml/ref/initdb.sgml
View File

@ -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>