</listitem>

</varlistentry>

<varlistentry>

<term><acronym>LSN</acronym></term>

<listitem>

<para>

Log Sequence Number, see <link linkend="datatype-pg-lsn"><type>pg_lsn</></link>

and <link linkend="wal-internals">WAL Internals</link>.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term><acronym>MSVC</acronym></term>

<listitem>

<sect1 id="wal-internals">

<title>WAL Internals</title>

<indexterm zone="wal-internals">

<primary>LSN</primary>

</indexterm>

<para>

<acronym>WAL</acronym> is automatically enabled; no action is

required from the administrator except ensuring that the

linkend="wal-configuration">).

</para>

<para>

<acronym>WAL</acronym> records are appended to the <acronym>WAL</acronym>

logs as each new record is written. The insert position is described by

a Log Sequence Number (<acronym>LSN</acronym>) that is a byte offset into

the logs, increasing monotonically with each new record.

<acronym>LSN</acronym> values are returned as the datatype

<link linkend="datatype-pg-lsn"><type>pg_lsn</></link>. Values can be

compared to calculate the volume of <acronym>WAL</acronym> data that

separates them, so they are used to measure the progress of replication

and recovery.

</para>

<para>

<acronym>WAL</acronym> logs are stored in the directory

<filename>pg_xlog</filename> under the data directory, as a set of