<!--

$Header: /cvsroot/pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.5 2002/08/29 22:19:03 petere Exp $

$Header: /cvsroot/pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.6 2002/10/02 21:30:13 tgl Exp $

PostgreSQL documentation

-->

<refnamediv>

<refname>pg_resetxlog</refname>

<refpurpose>reset write-ahead logfileandoptionally thepg_controlfile</refpurpose>

<refpurpose>reset write-ahead log and pg_controlcontents</refpurpose>

</refnamediv>

<refsynopsisdiv>

<cmdsynopsis>

<command>pg_resetxlog</command>

<arg> -f </arg>

<arg> -n </arg>

<arg> -o <replaceable class="parameter">oid</replaceable> </arg>

<arg> -x <replaceable class="parameter">xid</replaceable> </arg>

<arg> -l <replaceable class="parameter">fileid</replaceable>,<replaceable class="parameter">seg</replaceable> </arg>

<arg choice="plain"><replaceable>datadir</replaceable></arg>

<refsect1 id="R1-APP-PGRESETXLOG-1">

<title>Description</title>

<para>

<command>pg_resetxlog</command> clears the write-ahead log file and

optionally the <filename>pg_control</> file. This function is sometimes

<command>pg_resetxlog</command> clears the write-ahead log and

optionally resets some fields in the <filename>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.

<para>

If <command>pg_resetxlog</command> complains that it cannot determine

valid data for <filename>pg_control</>, you can force it to proceed anyway

by specifying the <literal>-f</> (force) switch. In this case plausible values

will be substituted for the missing data. If <literal>-f</> is used then

by specifying the <literal>-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.

<command>pg_resetxlog</command>'s own environment is the source for its

guess at the locale fields; take care that <envar>LANG</> and so forth

match the environment that <application>initdb</> was run in.

If you are not able to determine correct values for all these fields,

<literal>-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. <emphasis>Do not</>

execute any data-modifying operations in the database before you dump,

as any such action is likely to make the corruption worse.

</para>

<para>

The <literal>-o</>, <literal>-x</>, and <literal>-l</> switches allow

the next OID, next transaction ID, and WAL starting address values to

be set manually. These are only needed when

<command>pg_resetxlog</command> is unable to determine appropriate values

by reading <filename>pg_control</>. A safe value for the

next transaction ID may be determined by looking for the largest

file name in <envar>$PGDATA</><filename>/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 <filename>0011</> is the largest entry

in <filename>pg_clog</>, <literal>-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

<envar>$PGDATA</><filename>/pg_xlog</>. These also are in hex, and

have two parts. For example, if <filename>000000FF0000003A</> is the

largest entry in <filename>pg_xlog</>, <literal>-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.

</para>

<para>

The <literal>-n</> (no operation) switch instructs

<command>pg_resetxlog</command> to print the values reconstructed from

<filename>pg_control</> and then exit without modifying anything.

This is mainly a debugging tool, but may be useful as a sanity check

before allowing <command>pg_resetxlog</command> to proceed for real.

</para>

<para>

The <literal>-x</> and <literal>-l</> switches are intended for use by

<application>pg_upgrade</>. In most cases they should not be used in

manual recovery operations.

</para>

</refsect1>

<refsect1>

boolforce= false;

boolnoupdate= false;

TransactionIdset_xid=0;

Oidset_oid=0;

uint32minXlogId=0,

minXlogSeg=0;

char*endptr;

char*endptr2;

char*DataDir;

intfd;

charpath[MAXPGPATH];

}

while ((c=getopt(argc,argv,"fl:nx:"))!=-1)

while ((c=getopt(argc,argv,"fl:no:x:"))!=-1)

{

switch (c)

{

break;

case'x':

set_xid=strtoul(optarg,NULL,0);

set_xid=strtoul(optarg,&endptr,0);

if (endptr==optarg||*endptr!='\0')

{

fprintf(stderr,_("%s: invalid argument for -x option\n"),progname);

fprintf(stderr,_("Try '%s --help' for more information.\n"),progname);

exit(1);

}

if (set_xid==0)

{

fprintf(stderr,_("%s: transaction ID (-x) must not be 0\n"),progname);

exit(1);

}

break;

case'o':

set_oid=strtoul(optarg,&endptr,0);

if (endptr==optarg||*endptr!='\0')

{

fprintf(stderr,_("%s: invalid argument for -o option\n"),progname);

fprintf(stderr,_("Try '%s --help' for more information.\n"),progname);

exit(1);

}

if (set_oid==0)

{

fprintf(stderr,_("%s: OID (-o) must not be 0\n"),progname);

exit(1);

}

break;

case'l':

if (sscanf(optarg,"%u,%u",&minXlogId,&minXlogSeg)!=2)

minXlogId=strtoul(optarg,&endptr,0);

if (endptr==optarg||*endptr!=',')

{

fprintf(stderr,_("%s: invalid argument for -l option\n"),progname);

fprintf(stderr,_("Try '%s --help' for more information.\n"),progname);

exit(1);

}

minXlogSeg=strtoul(endptr+1,&endptr2,0);

if (endptr2==endptr+1||*endptr2!='\0')

{

fprintf(stderr,_("%s: invalid argument for -l option\n"),progname);

fprintf(stderr,_("Try '%s --help' for more information.\n"),progname);

if (!ReadControlFile())

GuessControlValues();

if (set_xid!=0)

ControlFile.checkPointCopy.nextXid=set_xid;

if (set_oid!=0)

ControlFile.checkPointCopy.nextOid=set_oid;

if (minXlogId>ControlFile.logId||

(minXlogId==ControlFile.logId&&

minXlogSeg>ControlFile.logSeg))

{

ControlFile.logId=minXlogId;

ControlFile.logSeg=minXlogSeg;

}

if (set_xid!=0)

ControlFile.checkPointCopy.nextXid=set_xid;

if (minXlogId>ControlFile.logId||

(minXlogId==ControlFile.logId&&minXlogSeg>ControlFile.logSeg))

{

ControlFile.logId=minXlogId;

ControlFile.logSeg=minXlogSeg;

}

RewriteControlFile();

KillExistingXLOG();

WriteEmptyXLOG();

printf(_(" -f force update to be done\n"));

printf(_(" -l FILEID,SEG force minimum WAL starting location for new transaction log\n"));

printf(_(" -n no update, just show extracted control values (for testing)\n"));

printf(_(" -o OID set next OID\n"));

printf(_(" -x XID set next transaction ID\n"));

printf(_("\nReport bugs to <pgsql-bugs@postgresql.org>.\n"));

}