Add new Non-Durable Settings documentation section.

Document that synchronous_commit can lose transactions in a db crash,
not just a OS crash.

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 174f98140026ec48ca4cd82e3a940aa9b72b3123..f218e698b243a163b8f2b1f1b894ef199b9a039b 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1,4 +1,4 @@
-
+
 
 
   Server Configuration
@@ -1463,7 +1463,8 @@ SET ENABLE_SEQSCAN TO OFF;
         really guaranteed to be safe against a server crash.  (The maximum
         delay is three times .)  Unlike
         , setting this parameter to off
-        does not create any risk of database inconsistency: a crash might
+        does not create any risk of database inconsistency: an operating
+        system or database crash crash might
         result in some recent allegedly-committed transactions being lost, but
         the database state will be just the same as if those transactions had
         been aborted cleanly.  So, turning synchronous_commit off

diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index 4b6768bb694428143ee16e7c28d9e79c0faf7f89..10e38f2eb3dde15597b66380fa1696a87723a0e4 100644 (file)
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -1,4 +1,4 @@
-
+
 
  
   Performance Tips
@@ -1104,4 +1104,66 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
   
   
 
+  
+   Non-Durable Settings
+
+   
+    non-durable
+   
+
+   
+    Durability is a database feature that guarantees the recording of
+    committed transactions even if if the server crashes or loses
+    power.  However, durability adds significant database overhead,
+    so if your site does not require such a guarantee,
+    PostgreSQL can be configured to run
+    much faster.  The following are configuration changes you can make
+    to improve performance in such cases;  they do not invalidate
+    commit guarantees related to database crashes, only abrupt operating
+    system stoppage, except as mentioned below:
+
+    
+     
+      
+       Place the database cluster's data directory in a memory-backed
+       file system (i.e. RAM disk).  This eliminates all
+       database disk I/O, but limits data storage to the amount of
+       available memory (and perhaps swap).
+      
+     
+
+     
+      
+       Turn off ;  there is no need to flush
+       data to disk.
+      
+     
+
+     
+      
+       Turn off ;  there is no need
+       to guard against partial page writes.
+      
+     
+
+     
+      
+       Increase  and 
+       linkend="guc-checkpoint-timeout"> ; this reduces the frequency
+       of checkpoints, but increases the storage requirements of
+       /pg_xlog.
+      
+     
+
+     
+      
+       Turn off ;  there might be no
+       need to write the WAL to disk on every
+       commit.  This does affect database crash transaction durability.
+      
+     
+    
+   
+  
+