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Add code to prevent transaction ID wraparound by enforcing a safe limit

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in GetNewTransactionId().  Since the limit value has to be computed
before we run any real transactions, this requires adding code to database
startup to scan pg_database and determine the oldest datfrozenxid.
This can conveniently be combined with the first stage of an attack on
the problem that the 'flat file' copies of pg_shadow and pg_group are
not properly updated during WAL recovery.  The code I've added to
startup resides in a new file src/backend/utils/init/flatfiles.c, and
it is responsible for rewriting the flat files as well as initializing
the XID wraparound limit value.  This will eventually allow us to get
rid of GetRawDatabaseInfo too, but we'll need an initdb so we can add
a trigger to pg_database.
This commit is contained in:
Tom Lane
2005-02-20 02:22:07 +00:00
parent 617d16f4ff
commit 60b2444cc3
15 changed files with 1191 additions and 571 deletions
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52
src/backend/commands/vacuum.c
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@@ -13,7 +13,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.300 2005/02/15 03:50:07 momjian Exp $
* $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.301 2005/02/20 02:21:34 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -32,6 +32,7 @@
#include "catalog/namespace.h"
#include "catalog/pg_database.h"
#include "catalog/pg_index.h"
#include "commands/dbcommands.h"
#include "commands/vacuum.h"
#include "executor/executor.h"
#include "miscadmin.h"
@@ -761,8 +762,13 @@ vac_update_dbstats(Oid dbid,
*
* Scan pg_database to determine the system-wide oldest datvacuumxid,
* and use it to truncate the transaction commit log (pg_clog).
* Also generate a warning if the system-wide oldest datfrozenxid
* seems to be in danger of wrapping around.
* Also update the XID wrap limit point maintained by varsup.c.
*
* We also generate a warning if the system-wide oldest datfrozenxid
* seems to be in danger of wrapping around. This is a long-in-advance
* warning; if we start getting uncomfortably close, GetNewTransactionId
* will generate more-annoying warnings, and ultimately refuse to issue
* any more new XIDs.
*
* The passed XIDs are simply the ones I just wrote into my pg_database
* entry. They're used to initialize the "min" calculations.
@@ -778,10 +784,17 @@ vac_truncate_clog(TransactionId vacuumXID, TransactionId frozenXID)
HeapScanDesc scan;
HeapTuple tuple;
int32 age;
NameData oldest_datname;
bool vacuumAlreadyWrapped = false;
bool frozenAlreadyWrapped = false;
/* init oldest_datname to sync with my frozenXID */
namestrcpy(&oldest_datname, get_database_name(MyDatabaseId));
/*
* Note: the "already wrapped" cases should now be impossible due to the
* defenses in GetNewTransactionId, but we keep them anyway.
*/
relation = heap_openr(DatabaseRelationName, AccessShareLock);
scan = heap_beginscan(relation, SnapshotNow, 0, NULL);
@@ -807,7 +820,10 @@ vac_truncate_clog(TransactionId vacuumXID, TransactionId frozenXID)
if (TransactionIdPrecedes(myXID, dbform->datfrozenxid))
frozenAlreadyWrapped = true;
else if (TransactionIdPrecedes(dbform->datfrozenxid, frozenXID))
{
frozenXID = dbform->datfrozenxid;
namecpy(&oldest_datname, &dbform->datname);
}
}
}
@@ -830,24 +846,30 @@ vac_truncate_clog(TransactionId vacuumXID, TransactionId frozenXID)
/* Truncate CLOG to the oldest vacuumxid */
TruncateCLOG(vacuumXID);
/* Give warning about impending wraparound problems */
/*
* Do not update varsup.c if we seem to have suffered wraparound
* already; the computed XID might be bogus.
*/
if (frozenAlreadyWrapped)
{
ereport(WARNING,
(errmsg("some databases have not been vacuumed in over 1 billion transactions"),
errhint("Better vacuum them soon, or you may have a wraparound failure.")));
return;
}
else
{
age = (int32) (myXID - frozenXID);
if (age > (int32) ((MaxTransactionId >> 3) * 3))
ereport(WARNING,
(errmsg("some databases have not been vacuumed in %d transactions",
age),
errhint("Better vacuum them within %d transactions, "
"or you may have a wraparound failure.",
(int32) (MaxTransactionId >> 1) - age)));
}
/* Update the wrap limit for GetNewTransactionId */
SetTransactionIdLimit(frozenXID, &oldest_datname);
/* Give warning about impending wraparound problems */
age = (int32) (myXID - frozenXID);
if (age > (int32) ((MaxTransactionId >> 3) * 3))
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
NameStr(oldest_datname),
(MaxTransactionId >> 1) - age),
errhint("To avoid a database shutdown, execute a full-database VACUUM in \"%s\".",
NameStr(oldest_datname))));
}