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$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.10 2005/04/28 21:47:10 tgl Exp $

$PostgreSQL: pgsql/doc/src/sgml/ref/pg_resetxlog.sgml,v 1.11 2005/06/08 15:50:21 tgl Exp $

PostgreSQL documentation

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

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

<arg> -m <replaceable class="parameter">mxid</replaceable> </arg>

<arg> -O <replaceable class="parameter">mxoff</replaceable> </arg>

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

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

</cmdsynopsis>

<title>Description</title>

<para>

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

optionally resets some other control information(stored in the

<filename>pg_control</> file). This function is sometimes needed

optionally resets some other control information stored 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>

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.

next transaction ID, next multi-transaction ID and offset,

WAL starting address, and database locale fields.

The first five 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 <command>initdb</> was run in.

</para>

<para>

The <literal>-o</>, <literal>-x</>, <literal>-m</>, and <literal>-l</>

The <literal>-o</>, <literal>-x</>, <literal>-m</>, <literal>-O</>,

and <literal>-l</>

switches allow the next OID, next transaction ID, next multi-transaction

ID, and WAL starting address values to

ID,next multi-transaction offset,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</>. Safe values may be determined as

</para>

</listitem>

<listitem>

<para>

A safe value for the next multi-transaction offset (<literal>-O</>)

may be determined by looking for the numerically largest

file name in the directory <filename>pg_multixact/members</> under the

data directory, adding one, and then multiplying by 65536. As above,

the file names are in hexadecimal, so the easiest way to do this is to

specify the switch value in hexadecimal and add four zeroes.

</para>

</listitem>

<listitem>

<para>

The WAL starting address (<literal>-l</>) should be

if (!relation->rd_istemp)

{

xlrec.target.node=relation->rd_node;

xlrec.target.tid=tuple->t_self;

xlrec.locking_xid=xid;

xlrec.xid_is_mxact= ((new_infomask&HEAP_XMAX_IS_MULTI)!=0);

xlrec.shared_lock= (mode==LockTupleShared);

rdata[0].data= (char*)&xlrec;

rdata[0].len=SizeOfHeapLock;

htup= (HeapTupleHeader)PageGetItem(page,lp);

htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |

HEAP_XMAX_INVALID |

HEAP_XMAX_IS_MULTI |

HEAP_IS_LOCKED |

HEAP_MOVED);

htup->t_infomask |=HEAP_XMAX_INVALID;

HeapTupleHeaderSetXmax(htup,record->xl_xid);

if (xlrec->xid_is_mxact)

htup->t_infomask |=HEAP_XMAX_IS_MULTI;

if (xlrec->shared_lock)

htup->t_infomask |=HEAP_XMAX_SHARED_LOCK;

htup->t_infomask |=HEAP_XMAX_EXCL_LOCK;

HeapTupleHeaderSetXmax(htup,xlrec->locking_xid);

HeapTupleHeaderSetCmax(htup,FirstCommandId);

htup->t_ctid=xlrec->target.tid;

strcat(buf,"shared_lock: ");

strcat(buf,"exclusive_lock: ");

if (xlrec->xid_is_mxact)

strcat(buf,"mxid ");

strcat(buf,"xid ");

sprintf(buf+strlen(buf),"%u ",xlrec->locking_xid);

out_target(buf,&(xlrec->target));

}