Change WAL-logging scheme for multixacts to be more like regular

transaction IDs, rather than like subtrans; in particular, the information
now survives a database restart.  Per previous discussion, this is
essential for PITR log shipping and for 2PC.

1 files changed, 21 insertions, 7 deletions

diff --git a/doc/src/sgml/ref/pg_resetxlog.sgml b/doc/src/sgml/ref/pg_resetxlog.sgml
index f5915adacd4..f4caa8b80e6 100644
--- a/doc/src/sgml/ref/pg_resetxlog.sgml
+++ b/doc/src/sgml/ref/pg_resetxlog.sgml
@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.10 2005/04/28 21:47:10 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.11 2005/06/08 15:50:21 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -23,6 +23,7 @@ PostgreSQL documentation
    <arg> -o <replaceable class="parameter">oid</replaceable> </arg>
    <arg> -x <replaceable class="parameter">xid</replaceable> </arg>
    <arg> -m <replaceable class="parameter">mxid</replaceable> </arg>
+   <arg> -O <replaceable class="parameter">mxoff</replaceable> </arg>
    <arg> -l <replaceable class="parameter">timelineid</replaceable>,<replaceable class="parameter">fileid</replaceable>,<replaceable class="parameter">seg</replaceable> </arg>
    <arg choice="plain"><replaceable>datadir</replaceable></arg>
   </cmdsynopsis>
@@ -32,8 +33,8 @@ PostgreSQL documentation
   <title>Description</title>
   <para>
    <command>pg_resetxlog</command> clears the write-ahead log (WAL) and
-   optionally resets some other control information (stored in the
-   <filename>pg_control</> file).  This function is sometimes needed
+   optionally resets some other control information stored in the
+   <filename>pg_control</> file.  This function is sometimes needed
    if these files have become corrupted.  It should be used only as a
    last resort, when the server will not start due to such corruption.
   </para>
@@ -60,8 +61,9 @@ PostgreSQL documentation
    by specifying the <literal>-f</> (force) switch.  In this case plausible
    values will be substituted for the missing data.  Most of the fields can be
    expected to match, but manual assistance may be needed for the next OID,
-   next transaction ID, WAL starting address, and database locale fields.
-   The first three of these can be set using the switches discussed below.
+   next transaction ID, next multi-transaction ID and offset,
+   WAL starting address, and database locale fields.
+   The first five of these can be set using the switches discussed below.
    <command>pg_resetxlog</command>'s own environment is the source for its
    guess at the locale fields; take care that <envar>LANG</> and so forth
    match the environment that <command>initdb</> was run in.
@@ -74,9 +76,10 @@ PostgreSQL documentation
   </para>
 
   <para>
-   The <literal>-o</>, <literal>-x</>, <literal>-m</>, and <literal>-l</>
+   The <literal>-o</>, <literal>-x</>, <literal>-m</>, <literal>-O</>,
+   and <literal>-l</>
    switches allow the next OID, next transaction ID, next multi-transaction
-   ID, and WAL starting address values to
+   ID, next multi-transaction offset, and WAL starting address values to
    be set manually.  These are only needed when
    <command>pg_resetxlog</command> is unable to determine appropriate values
    by reading <filename>pg_control</>.  Safe values may be determined as
@@ -110,6 +113,17 @@ PostgreSQL documentation
 
     <listitem>
      <para>
+      A safe value for the next multi-transaction offset (<literal>-O</>)
+      may be determined by looking for the numerically largest
+      file name in the directory <filename>pg_multixact/members</> under the
+      data directory, adding one, and then multiplying by 65536.  As above,
+      the file names are in hexadecimal, so the easiest way to do this is to
+      specify the switch value in hexadecimal and add four zeroes.
+     </para>
+    </listitem>
+
+    <listitem>
+     <para>
       The WAL starting address (<literal>-l</>) should be
       larger than any file name currently existing in
       the directory <filename>pg_xlog</> under the data directory.