PG_RESETXLOG(1) 					  PostgreSQL Server Applications					   PG_RESETXLOG(1)

NAME

       pg_resetxlog - reset write-ahead log and pg_control contents

SYNOPSIS

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

DESCRIPTION

       pg_resetxlog  clears  the  write-ahead  log  and optionally resets some fields in the pg_control 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 corruption.

       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  rea-
       sons, 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 corruption 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  usually 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 any-
       thing.  This is mainly a debugging tool, but may be useful as a sanity check before allowing pg_resetxlog to proceed for real.

NOTES

       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)