mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-09-28 00:21:50 +02:00
315 lines
11 KiB
C
315 lines
11 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* varsup.c
|
|
* postgres OID & XID variables support routines
|
|
*
|
|
* Copyright (c) 2000-2006, PostgreSQL Global Development Group
|
|
*
|
|
* IDENTIFICATION
|
|
* $PostgreSQL: pgsql/src/backend/access/transam/varsup.c,v 1.70 2006/03/05 15:58:22 momjian Exp $
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
|
|
#include "postgres.h"
|
|
|
|
#include "access/clog.h"
|
|
#include "access/subtrans.h"
|
|
#include "access/transam.h"
|
|
#include "miscadmin.h"
|
|
#include "storage/ipc.h"
|
|
#include "storage/proc.h"
|
|
#include "utils/builtins.h"
|
|
|
|
|
|
/* Number of OIDs to prefetch (preallocate) per XLOG write */
|
|
#define VAR_OID_PREFETCH 8192
|
|
|
|
/* pointer to "variable cache" in shared memory (set up by shmem.c) */
|
|
VariableCache ShmemVariableCache = NULL;
|
|
|
|
|
|
/*
|
|
* Allocate the next XID for my new transaction.
|
|
*/
|
|
TransactionId
|
|
GetNewTransactionId(bool isSubXact)
|
|
{
|
|
TransactionId xid;
|
|
|
|
/*
|
|
* During bootstrap initialization, we return the special bootstrap
|
|
* transaction id.
|
|
*/
|
|
if (IsBootstrapProcessingMode())
|
|
return BootstrapTransactionId;
|
|
|
|
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
|
|
|
|
xid = ShmemVariableCache->nextXid;
|
|
|
|
/*
|
|
* Check to see if it's safe to assign another XID. This protects against
|
|
* catastrophic data loss due to XID wraparound. The basic rules are:
|
|
* warn if we're past xidWarnLimit, and refuse to execute transactions if
|
|
* we're past xidStopLimit, unless we are running in a standalone backend
|
|
* (which gives an escape hatch to the DBA who ignored all those
|
|
* warnings).
|
|
*
|
|
* Test is coded to fall out as fast as possible during normal operation,
|
|
* ie, when the warn limit is set and we haven't violated it.
|
|
*/
|
|
if (TransactionIdFollowsOrEquals(xid, ShmemVariableCache->xidWarnLimit) &&
|
|
TransactionIdIsValid(ShmemVariableCache->xidWarnLimit))
|
|
{
|
|
if (IsUnderPostmaster &&
|
|
TransactionIdFollowsOrEquals(xid, ShmemVariableCache->xidStopLimit))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
|
|
errmsg("database is not accepting commands to avoid wraparound data loss in database \"%s\"",
|
|
NameStr(ShmemVariableCache->limit_datname)),
|
|
errhint("Stop the postmaster and use a standalone backend to vacuum database \"%s\".",
|
|
NameStr(ShmemVariableCache->limit_datname))));
|
|
else
|
|
ereport(WARNING,
|
|
(errmsg("database \"%s\" must be vacuumed within %u transactions",
|
|
NameStr(ShmemVariableCache->limit_datname),
|
|
ShmemVariableCache->xidWrapLimit - xid),
|
|
errhint("To avoid a database shutdown, execute a full-database VACUUM in \"%s\".",
|
|
NameStr(ShmemVariableCache->limit_datname))));
|
|
}
|
|
|
|
/*
|
|
* If we are allocating the first XID of a new page of the commit log,
|
|
* zero out that commit-log page before returning. We must do this while
|
|
* holding XidGenLock, else another xact could acquire and commit a later
|
|
* XID before we zero the page. Fortunately, a page of the commit log
|
|
* holds 32K or more transactions, so we don't have to do this very often.
|
|
*
|
|
* Extend pg_subtrans too.
|
|
*/
|
|
ExtendCLOG(xid);
|
|
ExtendSUBTRANS(xid);
|
|
|
|
/*
|
|
* Now advance the nextXid counter. This must not happen until after we
|
|
* have successfully completed ExtendCLOG() --- if that routine fails, we
|
|
* want the next incoming transaction to try it again. We cannot assign
|
|
* more XIDs until there is CLOG space for them.
|
|
*/
|
|
TransactionIdAdvance(ShmemVariableCache->nextXid);
|
|
|
|
/*
|
|
* We must store the new XID into the shared PGPROC array before releasing
|
|
* XidGenLock. This ensures that when GetSnapshotData calls
|
|
* ReadNewTransactionId, all active XIDs before the returned value of
|
|
* nextXid are already present in PGPROC. Else we have a race condition.
|
|
*
|
|
* XXX by storing xid into MyProc without acquiring ProcArrayLock, we are
|
|
* relying on fetch/store of an xid to be atomic, else other backends
|
|
* might see a partially-set xid here. But holding both locks at once
|
|
* would be a nasty concurrency hit (and in fact could cause a deadlock
|
|
* against GetSnapshotData). So for now, assume atomicity. Note that
|
|
* readers of PGPROC xid field should be careful to fetch the value only
|
|
* once, rather than assume they can read it multiple times and get the
|
|
* same answer each time.
|
|
*
|
|
* The same comments apply to the subxact xid count and overflow fields.
|
|
*
|
|
* A solution to the atomic-store problem would be to give each PGPROC its
|
|
* own spinlock used only for fetching/storing that PGPROC's xid and
|
|
* related fields.
|
|
*
|
|
* If there's no room to fit a subtransaction XID into PGPROC, set the
|
|
* cache-overflowed flag instead. This forces readers to look in
|
|
* pg_subtrans to map subtransaction XIDs up to top-level XIDs. There is a
|
|
* race-condition window, in that the new XID will not appear as running
|
|
* until its parent link has been placed into pg_subtrans. However, that
|
|
* will happen before anyone could possibly have a reason to inquire about
|
|
* the status of the XID, so it seems OK. (Snapshots taken during this
|
|
* window *will* include the parent XID, so they will deliver the correct
|
|
* answer later on when someone does have a reason to inquire.)
|
|
*/
|
|
if (MyProc != NULL)
|
|
{
|
|
if (!isSubXact)
|
|
MyProc->xid = xid;
|
|
else
|
|
{
|
|
if (MyProc->subxids.nxids < PGPROC_MAX_CACHED_SUBXIDS)
|
|
{
|
|
MyProc->subxids.xids[MyProc->subxids.nxids] = xid;
|
|
MyProc->subxids.nxids++;
|
|
}
|
|
else
|
|
MyProc->subxids.overflowed = true;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(XidGenLock);
|
|
|
|
return xid;
|
|
}
|
|
|
|
/*
|
|
* Read nextXid but don't allocate it.
|
|
*/
|
|
TransactionId
|
|
ReadNewTransactionId(void)
|
|
{
|
|
TransactionId xid;
|
|
|
|
LWLockAcquire(XidGenLock, LW_SHARED);
|
|
xid = ShmemVariableCache->nextXid;
|
|
LWLockRelease(XidGenLock);
|
|
|
|
return xid;
|
|
}
|
|
|
|
/*
|
|
* Determine the last safe XID to allocate given the currently oldest
|
|
* datfrozenxid (ie, the oldest XID that might exist in any database
|
|
* of our cluster).
|
|
*/
|
|
void
|
|
SetTransactionIdLimit(TransactionId oldest_datfrozenxid,
|
|
Name oldest_datname)
|
|
{
|
|
TransactionId xidWarnLimit;
|
|
TransactionId xidStopLimit;
|
|
TransactionId xidWrapLimit;
|
|
TransactionId curXid;
|
|
|
|
Assert(TransactionIdIsValid(oldest_datfrozenxid));
|
|
|
|
/*
|
|
* The place where we actually get into deep trouble is halfway around
|
|
* from the oldest potentially-existing XID. (This calculation is
|
|
* probably off by one or two counts, because the special XIDs reduce the
|
|
* size of the loop a little bit. But we throw in plenty of slop below,
|
|
* so it doesn't matter.)
|
|
*/
|
|
xidWrapLimit = oldest_datfrozenxid + (MaxTransactionId >> 1);
|
|
if (xidWrapLimit < FirstNormalTransactionId)
|
|
xidWrapLimit += FirstNormalTransactionId;
|
|
|
|
/*
|
|
* We'll refuse to continue assigning XIDs in interactive mode once we get
|
|
* within 1M transactions of data loss. This leaves lots of room for the
|
|
* DBA to fool around fixing things in a standalone backend, while not
|
|
* being significant compared to total XID space. (Note that since
|
|
* vacuuming requires one transaction per table cleaned, we had better be
|
|
* sure there's lots of XIDs left...)
|
|
*/
|
|
xidStopLimit = xidWrapLimit - 1000000;
|
|
if (xidStopLimit < FirstNormalTransactionId)
|
|
xidStopLimit -= FirstNormalTransactionId;
|
|
|
|
/*
|
|
* We'll start complaining loudly when we get within 10M transactions of
|
|
* the stop point. This is kind of arbitrary, but if you let your gas
|
|
* gauge get down to 1% of full, would you be looking for the next gas
|
|
* station? We need to be fairly liberal about this number because there
|
|
* are lots of scenarios where most transactions are done by automatic
|
|
* clients that won't pay attention to warnings. (No, we're not gonna make
|
|
* this configurable. If you know enough to configure it, you know enough
|
|
* to not get in this kind of trouble in the first place.)
|
|
*/
|
|
xidWarnLimit = xidStopLimit - 10000000;
|
|
if (xidWarnLimit < FirstNormalTransactionId)
|
|
xidWarnLimit -= FirstNormalTransactionId;
|
|
|
|
/* Grab lock for just long enough to set the new limit values */
|
|
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
|
|
ShmemVariableCache->xidWarnLimit = xidWarnLimit;
|
|
ShmemVariableCache->xidStopLimit = xidStopLimit;
|
|
ShmemVariableCache->xidWrapLimit = xidWrapLimit;
|
|
namecpy(&ShmemVariableCache->limit_datname, oldest_datname);
|
|
curXid = ShmemVariableCache->nextXid;
|
|
LWLockRelease(XidGenLock);
|
|
|
|
/* Log the info */
|
|
ereport(LOG,
|
|
(errmsg("transaction ID wrap limit is %u, limited by database \"%s\"",
|
|
xidWrapLimit, NameStr(*oldest_datname))));
|
|
/* Give an immediate warning if past the wrap warn point */
|
|
if (TransactionIdFollowsOrEquals(curXid, xidWarnLimit))
|
|
ereport(WARNING,
|
|
(errmsg("database \"%s\" must be vacuumed within %u transactions",
|
|
NameStr(*oldest_datname),
|
|
xidWrapLimit - curXid),
|
|
errhint("To avoid a database shutdown, execute a full-database VACUUM in \"%s\".",
|
|
NameStr(*oldest_datname))));
|
|
}
|
|
|
|
|
|
/*
|
|
* GetNewObjectId -- allocate a new OID
|
|
*
|
|
* OIDs are generated by a cluster-wide counter. Since they are only 32 bits
|
|
* wide, counter wraparound will occur eventually, and therefore it is unwise
|
|
* to assume they are unique unless precautions are taken to make them so.
|
|
* Hence, this routine should generally not be used directly. The only
|
|
* direct callers should be GetNewOid() and GetNewRelFileNode() in
|
|
* catalog/catalog.c.
|
|
*/
|
|
Oid
|
|
GetNewObjectId(void)
|
|
{
|
|
Oid result;
|
|
|
|
LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Check for wraparound of the OID counter. We *must* not return 0
|
|
* (InvalidOid); and as long as we have to check that, it seems a good
|
|
* idea to skip over everything below FirstNormalObjectId too. (This
|
|
* basically just avoids lots of collisions with bootstrap-assigned OIDs
|
|
* right after a wrap occurs, so as to avoid a possibly large number of
|
|
* iterations in GetNewOid.) Note we are relying on unsigned comparison.
|
|
*
|
|
* During initdb, we start the OID generator at FirstBootstrapObjectId, so
|
|
* we only enforce wrapping to that point when in bootstrap or standalone
|
|
* mode. The first time through this routine after normal postmaster
|
|
* start, the counter will be forced up to FirstNormalObjectId. This
|
|
* mechanism leaves the OIDs between FirstBootstrapObjectId and
|
|
* FirstNormalObjectId available for automatic assignment during initdb,
|
|
* while ensuring they will never conflict with user-assigned OIDs.
|
|
*/
|
|
if (ShmemVariableCache->nextOid < ((Oid) FirstNormalObjectId))
|
|
{
|
|
if (IsPostmasterEnvironment)
|
|
{
|
|
/* wraparound in normal environment */
|
|
ShmemVariableCache->nextOid = FirstNormalObjectId;
|
|
ShmemVariableCache->oidCount = 0;
|
|
}
|
|
else
|
|
{
|
|
/* we may be bootstrapping, so don't enforce the full range */
|
|
if (ShmemVariableCache->nextOid < ((Oid) FirstBootstrapObjectId))
|
|
{
|
|
/* wraparound in standalone environment? */
|
|
ShmemVariableCache->nextOid = FirstBootstrapObjectId;
|
|
ShmemVariableCache->oidCount = 0;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* If we run out of logged for use oids then we must log more */
|
|
if (ShmemVariableCache->oidCount == 0)
|
|
{
|
|
XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
|
|
ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
|
|
}
|
|
|
|
result = ShmemVariableCache->nextOid;
|
|
|
|
(ShmemVariableCache->nextOid)++;
|
|
(ShmemVariableCache->oidCount)--;
|
|
|
|
LWLockRelease(OidGenLock);
|
|
|
|
return result;
|
|
}
|