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RedHat 9 (Linux i386) - man page for pg_resetxlog (redhat section 1)

PG_RESETXLOG(1) 		  PostgreSQL Server Applications		  PG_RESETXLOG(1)

       pg_resetxlog - reset write-ahead log and pg_control contents

       pg_resetxlog [  -f  ] [	-n  ] [  -o oid  ] [  -x xid  ] [  -l fileid,seg  ] datadir

       pg_resetxlog  clears  the write-ahead log and optionally resets some fields in the pg_con-
       trol file. This function is sometimes needed if these files  have  become  corrupted.   It
       should  be  used only as a last resort, when the server will not start due to such corrup-

       After running this command, it should be possible to start the server, but  bear  in  mind
       that  the  database may contain inconsistent data due to partially-committed transactions.
       You should immediately dump your data, run initdb, and reload.  After  reload,  check  for
       inconsistencies and repair as needed.

       This  utility  can  only  be run by the user who installed the server, because it requires
       read/write access to the datadir.  For safety reasons, you must specify the data directory
       on the command line.  pg_resetxlog does not use the environment variable PGDATA.

       If  pg_resetxlog  complains  that  it  cannot determine valid data for pg_control, you can
       force it to proceed anyway by specifying the -f (force) switch.	In  this  case	plausible
       values  will  be  substituted  for the missing data. Most of the fields can be expected to
       match, but manual assistance may be needed for the next	OID,  next  transaction  ID,  WAL
       starting  address,  and database locale fields.	The first three of these can be set using
       the switches discussed below.  pg_resetxlog's own environment is the source for its  guess
       at  the	locale fields; take care that LANG and so forth match the environment that initdb
       was run in.  If you are not able to determine correct values for all these fields, -f  can
       still  be  used,  but the recovered database must be treated with even more suspicion than
       usual --- an immediate dump and reload is imperative. Do not  execute  any  data-modifying
       operations  in the database before you dump, as any such action is likely to make the cor-
       ruption worse.

       The -o, -x, and -l switches allow the next OID, next  transaction  ID,  and  WAL  starting
       address	values	to  be set manually. These are only needed when pg_resetxlog is unable to
       determine appropriate values by reading pg_control. A safe value for the next  transaction
       ID  may be determined by looking for the largest file name in $PGDATA/pg_clog, adding one,
       and then multiplying by 1048576. Note that the file names are in hexadecimal. It  is  usu-
       ally  easiest  to specify the switch value in hexadecimal too. For example, if 0011 is the
       largest entry in pg_clog, -x 0x1200000 will work (five trailing zeroes provide the  proper
       multiplier).   The  WAL	starting  address should be larger than any file number currently
       existing in $PGDATA/pg_xlog. These also are in hex, and have two parts.	For  example,  if
       000000FF0000003A  is  the  largest  entry in pg_xlog, -l 0xFF,0x3B will work.  There is no
       comparably easy way to determine a next OID that's beyond the largest one in the database,
       but fortunately it is not critical to get the next-OID setting right.

       The -n (no operation) switch instructs pg_resetxlog to print the values reconstructed from
       pg_control and then exit without modifying anything.  This is mainly a debugging tool, but
       may be useful as a sanity check before allowing pg_resetxlog to proceed for real.

       This  command must not be used when the postmaster is running. pg_resetxlog will refuse to
       start up if it finds a postmaster lock file in the datadir. If the postmaster crashed then
       a  lock file may have been left behind; in that case you can remove the lock file to allow
       pg_resetxlog to run. But before you do so, make doubly certain that there is no postmaster
       nor any backend server process still alive.

Application				    2002-11-22				  PG_RESETXLOG(1)

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