First cut at XLOG file reset utility.

Could do with more testing, but it works in the simple cases.

contrib/Makefile

-# $Header: /cvsroot/pgsql/contrib/Makefile,v 1.17 2001/03/13 19:28:02 petere Exp $
+# $Header: /cvsroot/pgsql/contrib/Makefile,v 1.18 2001/03/14 00:57:43 tgl Exp $
 
 subdir = contrib
 top_builddir = ..
@@ -18,8 +18,10 @@ WANTED_DIRS = \
 		miscutil	\
 		noupdate	\
 		oid2name	\
+		pg_controldata	\
 		pg_dumplo	\
 		pg_logger	\
+		pg_resetxlog	\
 		pgbench		\
 		pgcrypto	\
 		rserv		\

contrib/README

@@ -52,6 +52,10 @@ intarray -
 	by Teodor Sigaev <teodor@stack.net> and Oleg Bartunov
 	<oleg@sai.msu.su>.
 
+ipc_check -
+	Simple test script to help in configuring IPC.
+	FreeBSD only, for now.
+
 isbn_issn -
 	PostgreSQL type extensions for ISBN (books) and ISSN (serials)
 	by Garrett A. Wollman <wollman@khavrinen.lcs.mit.edu>
@@ -86,7 +90,7 @@ oid2name -
 	by B Palmer <bpalmer@crimelabs.net>
 
 pg_controldata -
-	Dump internal database site structures
+	Dump contents of pg_control (database master file)
 	by Oliver Elphick <olly@lfix.co.uk>
 
 pg_dumplo -
@@ -97,6 +101,10 @@ pg_logger -
 	Stdin-to-syslog gateway for PostgreSQL
 	by Nathan Myers <ncm@nospam.cantrip.org>
 
+pg_resetxlog -
+	Reset the WAL log (pg_xlog) to recover from crash or format change
+	by Tom Lane <tgl@sss.pgh.pa.us>
+
 pgbench -
 	TPC-B like benchmarking tool
 	by Tatsuo Ishii <t-ishii@sra.co.jp>

contrib/pg_resetxlog/Makefile

+#
+# $Header: /cvsroot/pgsql/contrib/pg_resetxlog/Attic/Makefile,v 1.1 2001/03/14 00:57:43 tgl Exp $
+#
+
+subdir = contrib/pg_resetxlog
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS	= pg_resetxlog.o pg_crc.o
+
+all: pg_resetxlog
+
+pg_resetxlog: $(OBJS)
+	$(CC) $(CFLAGS) $(OBJS) $(LDFLAGS) $(LIBS) -o $@
+
+pg_crc.c: $(top_builddir)/src/backend/utils/hash/pg_crc.c
+	rm -f $@ && $(LN_S) $< .
+
+install: all installdirs
+	$(INSTALL_PROGRAM) pg_resetxlog$(X)	$(bindir)
+	$(INSTALL_DATA) README.pg_resetxlog	$(docdir)/contrib
+
+installdirs:
+	$(mkinstalldirs) $(bindir) $(docdir)/contrib
+
+uninstall:
+	rm -f $(bindir)/pg_resetxlog$(X) $(docdir)/contrib/README.pg_resetxlog
+
+clean distclean maintainer-clean:
+	rm -f pg_resetxlog$(X) $(OBJS) pg_crc.c
+
+depend dep:
+	$(CC) -MM -MG $(CFLAGS) *.c > depend
+
+ifeq (depend,$(wildcard depend))
+include depend
+endif

contrib/pg_resetxlog/README.pg_resetxlog

+pg_resetxlog is a program to clear the WAL transaction log (stored in
+$PGDATA/pg_xlog/), replacing whatever had been in it with just a dummy
+shutdown-checkpoint record.  It also regenerates the pg_control file
+if necessary.
+
+THIS PROGRAM WILL DESTROY VALUABLE LOG DATA!!!  Don't run it unless you
+really need it!!!
+
+pg_resetxlog is primarily intended for disaster recovery --- that is,
+if your pg_control and/or xlog are hosed badly enough that Postgres refuses
+to start up, this program will get you past that problem and let you get to
+your data files.  But realize that without the xlog, your data files may be
+corrupt due to partially-applied transactions, incomplete index-file
+updates, etc.  You should dump your data, check it for accuracy, then initdb
+and reload.
+
+A secondary purpose is to cope with xlog format changes without requiring
+initdb.  To use pg_resetxlog for this purpose, just be sure that you have
+cleanly shut down your old postmaster (if you're not sure, see the contrib
+module pg_controldata and run it to be sure the DB state is SHUTDOWN).
+Then run pg_resetxlog, and finally install and start the new version of
+the database software.
+
+To run the program, make sure your postmaster is not running, then
+(as the Postgres admin user) do
+
+	pg_resetxlog $PGDATA
+
+As a safety measure, the target data directory must be specified on the
+command line, it cannot be defaulted.
+
+If pg_resetxlog complains that it can't reconstruct valid data for pg_control,
+you can force it to invent plausible data values with
+
+	pg_resetxlog -f $PGDATA
+
+If this turns out to be necessary then you *definitely* should plan on
+immediate dump, initdb, reload --- any modifications you do to the database
+after "pg_resetxlog -f" would be likely to corrupt things even worse.