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Make the server track an 'XID epoch', that is, maintain higher-order bits

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of the transaction ID counter.  Nothing is done with the epoch except to
store it in checkpoint records, but this provides a foundation with which
add-on code can pretend that XIDs never wrap around.  This is a severely
trimmed and rewritten version of the xxid patch submitted by Marko Kreen.
Per discussion, the epoch counter seems the only part of xxid that really
needs to be in the core server.
This commit is contained in:
Tom Lane
2006-08-21 16:16:31 +00:00
parent 1054c38069
commit 35af5422f6
6 changed files with 177 additions and 44 deletions
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28
doc/src/sgml/ref/pg_resetxlog.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.16 2006/06/18 15:38:36 petere Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.17 2006/08/21 16:16:31 tgl Exp $
PostgreSQL documentation
-->
@ -22,6 +22,7 @@ PostgreSQL documentation
<arg>-n</arg>
<arg>-o<replaceable class="parameter">oid</replaceable> </arg>
<arg>-x <replaceable class="parameter">xid</replaceable> </arg>
<arg>-e <replaceable class="parameter">xid_epoch</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>
@ -61,9 +62,9 @@ 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, next multitransaction ID and offset,
next transaction ID and epoch, next multitransaction ID and offset,
WAL starting address, and database locale fields.
The first five of these can be set using the switches discussed below.
The first six 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.
@ -76,11 +77,12 @@ PostgreSQL documentation
</para>
<para>
The <literal>-o</>, <literal>-x</>, <literal>-m</>, <literal>-O</>,
The <literal>-o</>, <literal>-x</>, <literal>-e</>,
<literal>-m</>, <literal>-O</>,
and <literal>-l</>
switches allow the next OID, next transaction ID, next multitransaction
ID, next multitransaction offset, and WAL starting address values to
be set manually. These are only needed when
switches allow the next OID, next transaction ID, next transaction ID's
epoch, next multitransaction ID, next multitransaction 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
follows:
@ -146,6 +148,18 @@ PostgreSQL documentation
get the next-OID setting right.
</para>
</listitem>
<listitem>
<para>
The transaction ID epoch is not actually stored anywhere in the database
except in the field that is set by <command>pg_resetxlog</command>,
so any value will work so far as the database itself is concerned.
You might need to adjust this value to ensure that replication
systems such as <application>Slony-I</> work correctly &mdash;
if so, an appropriate value should be obtainable from the state of
the downstream replicated database.
</para>
</listitem>
</itemizedlist>
</para>