Document LSN acronym in WAL Internals

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

Simon Riggs and Michael Paquier

diff --git a/doc/src/sgml/acronyms.sgml b/doc/src/sgml/acronyms.sgml
index 38f111ef9d98a786769d090897dbe31335ab8d4e..bf2273fa8a09705190e53b1add3a98f05952d157 100644 (file)
--- a/doc/src/sgml/acronyms.sgml
+++ b/doc/src/sgml/acronyms.sgml
@@ -380,6 +380,16 @@
     
    
 
+   
+    LSN
+    
+     
+      Log Sequence Number, see pg_lsn
+      and WAL Internals.
+     
+    
+   
+
    
     MSVC
     

diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 503ea8a2a7e913d1be7df792f2b1e7b092ee5c7f..9ae65477218c660084888315eb357380eccd0de1 100644 (file)
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -724,6 +724,10 @@
  
   WAL Internals
 
+  
+   LSN
+  
+
   
    WAL is automatically enabled; no action is
    required from the administrator except ensuring that the
@@ -732,6 +736,18 @@
    linkend="wal-configuration">).
   
 
+  
+   WAL records are appended to the WAL
+   logs as each new record is written. The insert position is described by
+   a Log Sequence Number (LSN) that is a byte offset into
+   the logs, increasing monotonically with each new record.
+   LSN values are returned as the datatype
+   pg_lsn. Values can be
+   compared to calculate the volume of WAL data that
+   separates them, so they are used to measure the progress of replication
+   and recovery.
+  
+
   
    WAL logs are stored in the directory
    pg_xlog under the data directory, as a set of