pgdevel / src / include / catalog / catversion.h

 * catversion.h
 *	  "Catalog version number" for PostgreSQL.
 * The catalog version number is used to flag incompatible changes in
 * the PostgreSQL system catalogs.	Whenever anyone changes the format of
 * a system catalog relation, or adds, deletes, or modifies standard
 * catalog entries in such a way that an updated backend wouldn't work
 * with an old database (or vice versa), the catalog version number
 * should be changed.  The version number stored in pg_control by initdb
 * is checked against the version number compiled into the backend at
 * startup time, so that a backend can refuse to run in an incompatible
 * database.
 * The point of this feature is to provide a finer grain of compatibility
 * checking than is possible from looking at the major version number
 * stored in PG_VERSION.  It shouldn't matter to end users, but during
 * development cycles we usually make quite a few incompatible changes
 * to the contents of the system catalogs, and we don't want to bump the
 * major version number for each one.  What we can do instead is bump
 * this internal version number.  This should save some grief for
 * developers who might otherwise waste time tracking down "bugs" that
 * are really just code-vs-database incompatibilities.
 * The rule for developers is: if you commit a change that requires
 * an initdb, you should update the catalog version number (as well as
 * notifying the pghackers mailing list, which has been the informal
 * practice for a long time).
 * The catalog version number is placed here since modifying files in
 * include/catalog is the most common kind of initdb-forcing change.
 * But it could be used to protect any kind of incompatible change in
 * database contents or layout, such as altering tuple headers.
 * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 * src/include/catalog/catversion.h

 * We could use anything we wanted for version numbers, but I recommend
 * following the "YYYYMMDDN" style often used for DNS zone serial numbers.
 * YYYYMMDD are the date of the change, and N is the number of the change
 * on that day.  (Hopefully we'll never commit ten independent sets of
 * catalog changes on the same day...)

/*							yyyymmddN */
#define CATALOG_VERSION_NO	201112231