Update storage.sgml to describe the 9.0 tablespace directory layout.

diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index dd6f55ad637f79be7d93c160d5949f12b4aedd65..260df3de71ec3ccff9f9ee771cc1def2af417885 100644 (file)
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -174,8 +174,6 @@ adjusted using the configuration option --with-segsize
 when building PostgreSQL.)
 In principle, free space map and visibility map forks could require multiple
 segments as well, though this is unlikely to happen in practice.
-The contents of tables and indexes are discussed further in
-.
 
 
 
@@ -187,15 +185,27 @@ its TOAST table, if any.
 See  for more information.
 
 
+
+The contents of tables and indexes are discussed further in
+.
+
+
 
 Tablespaces make the scenario more complicated.  Each user-defined tablespace
 has a symbolic link inside the PGDATA/pg_tblspc
-directory, which points to the physical tablespace directory (as specified in
-its CREATE TABLESPACE command).  The symbolic link is named after
+directory, which points to the physical tablespace directory (i.e., the
+location specified in the tablespace's CREATE TABLESPACE command).
+This symbolic link is named after
 the tablespace's OID.  Inside the physical tablespace directory there is
+a subdirectory with a name that depends on the PostgreSQL
+server version, such as PG_9.0_201008051.  (The reason for using
+this subdirectory is so that successive versions of the database can use
+the same CREATE TABLESPACE location value without conflicts.)
+Within the version-specific subdirectory, there is
 a subdirectory for each database that has elements in the tablespace, named
-after the database's OID.  Tables within that directory follow the filenode
-naming scheme.  The pg_default tablespace is not accessed through
+after the database's OID.  Tables and indexes are stored within that
+directory, using the filenode naming scheme.
+The pg_default tablespace is not accessed through
 pg_tblspc, but corresponds to
 PGDATA/base.  Similarly, the pg_global
 tablespace is not accessed through pg_tblspc, but corresponds to