-<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.29 2004/08/08 04:34:43 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/wal.sgml,v 1.30 2004/11/15 04:35:57 neilc Exp $ -->
<chapter id="wal">
<title>Write-Ahead Logging (<acronym>WAL</acronym>)</title>
</para>
<para>
- <firstterm>Checkpoints</firstterm><indexterm><primary>checkpoint</></> are points in the sequence of
- transactions at which it is guaranteed that the data files have
- been updated with all information logged before the checkpoint. At
- checkpoint time, all dirty data pages are flushed to disk and a
- special checkpoint record is written to the log file. As result, in
- the event of a crash, the recoverer knows from what point in the
- log (known as the redo record) it should start the REDO operation,
- since any changes made to data files before that record are already
- on disk. After a checkpoint has been made, any log segments written
- before the redo record are no longer needed and can be recycled or
- removed. (When <acronym>WAL</acronym> archiving is being done, the
+ <firstterm>Checkpoints</firstterm><indexterm><primary>checkpoint</></>
+ are points in the sequence of transactions at which it is guaranteed
+ that the data files have been updated with all information logged before
+ the checkpoint. At checkpoint time, all dirty data pages are flushed to
+ disk and a special checkpoint record is written to the log file. As a
+ result, in the event of a crash, the crash recovery procedure knows from
+ what point in the log (known as the redo record) it should start the
+ REDO operation, since any changes made to data files before that point
+ are already on disk. After a checkpoint has been made, any log segments
+ written before the redo record are no longer needed and can be recycled
+ or removed. (When <acronym>WAL</acronym> archiving is being done, the
log segments must be archived before being recycled or removed.)
</para>