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Document LSN acronym in WAL Internals

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We previously didn't mention what an LSN actually was.

Simon Riggs and Michael Paquier
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Simon Riggs
2016-09-05 09:47:49 +01:00
parent d851bef2d6
commit ec03f4121c
2 changed files with 26 additions and 0 deletions
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doc/src/sgml/wal.sgml
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@@ -724,6 +724,10 @@
<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
@@ -732,6 +736,18 @@
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