greenplumn varsup 源码
greenplumn varsup 代码
文件路径：/src/backend/access/transam/varsup.c
/*-------------------------------------------------------------------------
*
* varsup.c
* postgres OID & XID variables support routines
*
* Copyright (c) 2000-2019, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/access/transam/varsup.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/clog.h"
#include "access/commit_ts.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "commands/dbcommands.h"
#include "miscadmin.h"
#include "postmaster/autovacuum.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "utils/faultinjector.h"
#include "utils/guc.h"
#include "utils/syscache.h"
#include "access/distributedlog.h"
#include "cdb/cdbvars.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;
int xid_stop_limit;
int xid_warn_limit;
/*
* Allocate the next FullTransactionId for a new transaction or
* subtransaction.
*
* The new XID is also stored into MyPgXact before returning.
*
* Note: when this is called, we are actually already inside a valid
* transaction, since XIDs are now not allocated until the transaction
* does something. So it is safe to do a database lookup if we want to
* issue a warning about XID wrap.
*/
FullTransactionId
GetNewTransactionId(bool isSubXact)
{
FullTransactionId full_xid;
TransactionId xid;
/*
* Workers synchronize transaction state at the beginning of each parallel
* operation, so we can't account for new XIDs after that point.
*/
if (IsInParallelMode())
elog(ERROR, "cannot assign TransactionIds during a parallel operation");
/*
* During bootstrap initialization, we return the special bootstrap
* transaction id.
*/
if (IsBootstrapProcessingMode())
{
Assert(!isSubXact);
MyPgXact->xid = BootstrapTransactionId;
return FullTransactionIdFromEpochAndXid(0, BootstrapTransactionId);
}
/* safety check, we should never get this far in a HS standby */
if (RecoveryInProgress())
elog(ERROR, "cannot assign TransactionIds during recovery");
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
full_xid = ShmemVariableCache->nextFullXid;
xid = XidFromFullTransactionId(full_xid);
/*----------
* 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:
*
* If we're past xidVacLimit, start trying to force autovacuum cycles.
* If we're past xidWarnLimit, start issuing warnings.
* If we're past xidStopLimit, refuse to execute transactions, unless
* we are running in single-user mode (which gives an escape hatch
* to the DBA who somehow got past the earlier defenses).
*
* Note that this coding also appears in GetNewMultiXactId.
*----------
*/
if (TransactionIdFollowsOrEquals(xid, ShmemVariableCache->xidVacLimit))
{
/*
* For safety's sake, we release XidGenLock while sending signals,
* warnings, etc. This is not so much because we care about
* preserving concurrency in this situation, as to avoid any
* possibility of deadlock while doing get_database_name(). First,
* copy all the shared values we'll need in this path.
*/
TransactionId xidWarnLimit = ShmemVariableCache->xidWarnLimit;
TransactionId xidStopLimit = ShmemVariableCache->xidStopLimit;
TransactionId xidWrapLimit = ShmemVariableCache->xidWrapLimit;
Oid oldest_datoid = ShmemVariableCache->oldestXidDB;
LWLockRelease(XidGenLock);
/*
* To avoid swamping the postmaster with signals, we issue the autovac
* request only once per 64K transaction starts. This still gives
* plenty of chances before we get into real trouble.
*/
if (IsUnderPostmaster && (xid % 65536) == 0)
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
if (IsUnderPostmaster &&
TransactionIdFollowsOrEquals(xid, xidStopLimit))
{
char *oldest_datname = get_database_name(oldest_datoid);
/*
* In GPDB, don't say anything about old prepared transactions, because the system
* only uses prepared transactions internally. PREPARE TRANSACTION is not available
* to users.
*/
/* complain even if that DB has disappeared */
if (oldest_datname)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("database is not accepting commands to avoid wraparound data loss in database \"%s\"",
oldest_datname),
errhint("Shutdown Greenplum Database. Lower the xid_stop_limit GUC. Execute a database-wide VACUUM in that database. Reset the xid_stop_limit GUC."
)));
else
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("database is not accepting commands to avoid wraparound data loss in database with OID %u",
oldest_datoid),
errhint("Shutdown Greenplum Database. Lower the xid_stop_limit GUC. Execute a database-wide VACUUM in that database. Reset the xid_stop_limit GUC."
)));
}
else if (TransactionIdFollowsOrEquals(xid, xidWarnLimit))
{
char *oldest_datname = get_database_name(oldest_datoid);
/*
* In GPDB, don't say anything about old prepared transactions, because the system
* only uses prepared transactions internally. PREPARE TRANSACTION is not available
* to users.
*/
/* complain even if that DB has disappeared */
if (oldest_datname)
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
oldest_datname,
xidWrapLimit - xid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
else
ereport(WARNING,
(errmsg("database with OID %u must be vacuumed within %u transactions",
oldest_datoid,
xidWrapLimit - xid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
}
/* Re-acquire lock and start over */
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
full_xid = ShmemVariableCache->nextFullXid;
xid = XidFromFullTransactionId(full_xid);
}
/*
* 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 and pg_commit_ts too.
*/
ExtendCLOG(xid);
ExtendCommitTs(xid);
ExtendSUBTRANS(xid);
DistributedLog_Extend(xid);
/*
* Now advance the nextFullXid 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.
*/
FullTransactionIdAdvance(&ShmemVariableCache->nextFullXid);
/*
* To aid testing, you can set the debug_burn_xids GUC, to consume XIDs
* faster. If set, we bump the XID counter to the next value divisible by
* 4096, minus one. The idea is to skip over "boring" XID ranges, but
* still step through XID wraparound, CLOG page boundaries etc. one XID
* at a time.
*/
if (Debug_burn_xids)
{
uint64 xx;
uint32 r;
/*
* Based on the minimum of ENTRIES_PER_PAGE (DistributedLog),
* SUBTRANS_XACTS_PER_PAGE, CLOG_XACTS_PER_PAGE.
*/
const uint64 page_extend_limit = 4 * 1024;
xx = U64FromFullTransactionId(ShmemVariableCache->nextFullXid);
r = xx % page_extend_limit;
if (r > 1 && r < (page_extend_limit - 1))
{
xx += page_extend_limit - r - 1;
ShmemVariableCache->nextFullXid.value = xx;
}
}
/*
* We must store the new XID into the shared ProcArray before releasing
* XidGenLock. This ensures that every active XID older than
* latestCompletedXid is present in the ProcArray, which is essential for
* correct OldestXmin tracking; see src/backend/access/transam/README.
*
* Note that readers of PGXACT xid fields should be careful to fetch the
* value only once, rather than assume they can read a value multiple
* times and get the same answer each time. Note we are assuming that
* TransactionId and int fetch/store are atomic.
*
* The same comments apply to the subxact xid count and overflow fields.
*
* Use of a write barrier prevents dangerous code rearrangement in this
* function; other backends could otherwise e.g. be examining my subxids
* info concurrently, and we don't want them to see an invalid
* intermediate state, such as an incremented nxids before the array entry
* is filled.
*
* Other processes that read nxids should do so before reading xids
* elements with a pg_read_barrier() in between, so that they can be sure
* not to read an uninitialized array element; see
* src/backend/storage/lmgr/README.barrier.
*
* 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 (!isSubXact)
MyPgXact->xid = xid; /* LWLockRelease acts as barrier */
else
{
int nxids = MyPgXact->nxids;
if (nxids < PGPROC_MAX_CACHED_SUBXIDS)
{
MyProc->subxids.xids[nxids] = xid;
pg_write_barrier();
MyPgXact->nxids = nxids + 1;
}
else
MyPgXact->overflowed = true;
}
LWLockRelease(XidGenLock);
return full_xid;
}
/*
* Read nextFullXid but don't allocate it.
*/
FullTransactionId
ReadNextFullTransactionId(void)
{
FullTransactionId fullXid;
LWLockAcquire(XidGenLock, LW_SHARED);
fullXid = ShmemVariableCache->nextFullXid;
LWLockRelease(XidGenLock);
return fullXid;
}
/*
* Advance nextFullXid to the value after a given xid. The epoch is inferred.
* This must only be called during recovery or from two-phase start-up code.
*/
void
AdvanceNextFullTransactionIdPastXid(TransactionId xid)
{
FullTransactionId newNextFullXid;
TransactionId next_xid;
uint32 epoch;
/*
* It is safe to read nextFullXid without a lock, because this is only
* called from the startup process or single-process mode, meaning that no
* other process can modify it.
*/
Assert(AmStartupProcess() || !IsUnderPostmaster);
/* Fast return if this isn't an xid high enough to move the needle. */
next_xid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
if (!TransactionIdFollowsOrEquals(xid, next_xid))
return;
/*
* Compute the FullTransactionId that comes after the given xid. To do
* this, we preserve the existing epoch, but detect when we've wrapped
* into a new epoch. This is necessary because WAL records and 2PC state
* currently contain 32 bit xids. The wrap logic is safe in those cases
* because the span of active xids cannot exceed one epoch at any given
* point in the WAL stream.
*/
TransactionIdAdvance(xid);
epoch = EpochFromFullTransactionId(ShmemVariableCache->nextFullXid);
if (unlikely(xid < next_xid))
++epoch;
newNextFullXid = FullTransactionIdFromEpochAndXid(epoch, xid);
/*
* We still need to take a lock to modify the value when there are
* concurrent readers.
*/
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
ShmemVariableCache->nextFullXid = newNextFullXid;
LWLockRelease(XidGenLock);
}
/*
* Advance the cluster-wide value for the oldest valid clog entry.
*
* We must acquire CLogTruncationLock to advance the oldestClogXid. It's not
* necessary to hold the lock during the actual clog truncation, only when we
* advance the limit, as code looking up arbitrary xids is required to hold
* CLogTruncationLock from when it tests oldestClogXid through to when it
* completes the clog lookup.
*/
void
AdvanceOldestClogXid(TransactionId oldest_datfrozenxid)
{
LWLockAcquire(CLogTruncationLock, LW_EXCLUSIVE);
if (TransactionIdPrecedes(ShmemVariableCache->oldestClogXid,
oldest_datfrozenxid))
{
ShmemVariableCache->oldestClogXid = oldest_datfrozenxid;
}
LWLockRelease(CLogTruncationLock);
}
/*
* Determine the last safe XID to allocate using the currently oldest
* datfrozenxid (ie, the oldest XID that might exist in any database
* of our cluster), and the OID of the (or a) database with that value.
*/
void
SetTransactionIdLimit(TransactionId oldest_datfrozenxid, Oid oldest_datoid)
{
TransactionId xidVacLimit;
TransactionId xidWarnLimit;
TransactionId xidStopLimit;
TransactionId xidWrapLimit;
TransactionId curXid;
Assert(TransactionIdIsNormal(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 xid_stop_limit 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 - (TransactionId)xid_stop_limit;
if (xidStopLimit < FirstNormalTransactionId)
xidStopLimit -= FirstNormalTransactionId;
/*
* We'll start complaining loudly when we get within xid_warn_limit 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 - (TransactionId)xid_warn_limit;
if (xidWarnLimit < FirstNormalTransactionId)
xidWarnLimit -= FirstNormalTransactionId;
/*
* We'll start trying to force autovacuums when oldest_datfrozenxid gets
* to be more than autovacuum_freeze_max_age transactions old.
*
* Note: guc.c ensures that autovacuum_freeze_max_age is in a sane range,
* so that xidVacLimit will be well before xidWarnLimit.
*
* Note: autovacuum_freeze_max_age is a PGC_POSTMASTER parameter so that
* we don't have to worry about dealing with on-the-fly changes in its
* value. It doesn't look practical to update shared state from a GUC
* assign hook (too many processes would try to execute the hook,
* resulting in race conditions as well as crashes of those not connected
* to shared memory). Perhaps this can be improved someday. See also
* SetMultiXactIdLimit.
*/
xidVacLimit = oldest_datfrozenxid + autovacuum_freeze_max_age;
if (xidVacLimit < FirstNormalTransactionId)
xidVacLimit += FirstNormalTransactionId;
/* Grab lock for just long enough to set the new limit values */
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
ShmemVariableCache->oldestXid = oldest_datfrozenxid;
ShmemVariableCache->xidVacLimit = xidVacLimit;
ShmemVariableCache->xidWarnLimit = xidWarnLimit;
ShmemVariableCache->xidStopLimit = xidStopLimit;
ShmemVariableCache->xidWrapLimit = xidWrapLimit;
ShmemVariableCache->oldestXidDB = oldest_datoid;
curXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
LWLockRelease(XidGenLock);
/* Log the info */
ereport(DEBUG1,
(errmsg("transaction ID wrap limit is %u, limited by database with OID %u",
xidWrapLimit, oldest_datoid)));
/*
* If past the autovacuum force point, immediately signal an autovac
* request. The reason for this is that autovac only processes one
* database per invocation. Once it's finished cleaning up the oldest
* database, it'll call here, and we'll signal the postmaster to start
* another iteration immediately if there are still any old databases.
*/
if (TransactionIdFollowsOrEquals(curXid, xidVacLimit) &&
IsUnderPostmaster && !InRecovery)
SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER);
/* Give an immediate warning if past the wrap warn point */
if (TransactionIdFollowsOrEquals(curXid, xidWarnLimit) && !InRecovery)
{
char *oldest_datname;
/*
* We can be called when not inside a transaction, for example during
* StartupXLOG(). In such a case we cannot do database access, so we
* must just report the oldest DB's OID.
*
* Note: it's also possible that get_database_name fails and returns
* NULL, for example because the database just got dropped. We'll
* still warn, even though the warning might now be unnecessary.
*/
if (IsTransactionState())
oldest_datname = get_database_name(oldest_datoid);
else
oldest_datname = NULL;
if (oldest_datname)
ereport(WARNING,
(errmsg("database \"%s\" must be vacuumed within %u transactions",
oldest_datname,
xidWrapLimit - curXid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
else
ereport(WARNING,
(errmsg("database with OID %u must be vacuumed within %u transactions",
oldest_datoid,
xidWrapLimit - curXid),
errhint("To avoid a database shutdown, execute a database-wide VACUUM in that database.\n"
"You might also need to commit or roll back old prepared transactions, or drop stale replication slots.")));
}
}
/*
* ForceTransactionIdLimitUpdate -- does the XID wrap-limit data need updating?
*
* We primarily check whether oldestXidDB is valid. The cases we have in
* mind are that that database was dropped, or the field was reset to zero
* by pg_resetwal. In either case we should force recalculation of the
* wrap limit. Also do it if oldestXid is old enough to be forcing
* autovacuums or other actions; this ensures we update our state as soon
* as possible once extra overhead is being incurred.
*/
bool
ForceTransactionIdLimitUpdate(void)
{
TransactionId nextXid;
TransactionId xidVacLimit;
TransactionId oldestXid;
Oid oldestXidDB;
/* Locking is probably not really necessary, but let's be careful */
LWLockAcquire(XidGenLock, LW_SHARED);
nextXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
xidVacLimit = ShmemVariableCache->xidVacLimit;
oldestXid = ShmemVariableCache->oldestXid;
oldestXidDB = ShmemVariableCache->oldestXidDB;
LWLockRelease(XidGenLock);
if (!TransactionIdIsNormal(oldestXid))
return true; /* shouldn't happen, but just in case */
if (!TransactionIdIsValid(xidVacLimit))
return true; /* this shouldn't happen anymore either */
if (TransactionIdFollowsOrEquals(nextXid, xidVacLimit))
return true; /* past VacLimit, don't delay updating */
if (!SearchSysCacheExists1(DATABASEOID, ObjectIdGetDatum(oldestXidDB)))
return true; /* could happen, per comments above */
return false;
}
/*
* Requires OidGenLock to be held by caller.
*/
static Oid
GetNewObjectIdUnderLock(void)
{
Oid result;
/* safety check, we should never get this far in a HS standby */
if (RecoveryInProgress())
elog(ERROR, "cannot assign OIDs during recovery");
Assert(LWLockHeldByMe(OidGenLock));
/*
* Check for wraparound of the OID counter. We *must* not return 0
* (InvalidOid), and in normal operation we mustn't return anything below
* FirstNormalObjectId since that range is reserved for initdb (see
* IsCatalogRelationOid()). Note we are relying on unsigned comparison.
*
* During initdb, we start the OID generator at FirstBootstrapObjectId, so
* we only wrap if before 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, or first post-initdb assignment, in normal mode */
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 mode (unlikely but possible) */
ShmemVariableCache->nextOid = FirstNormalObjectId;
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)--;
#ifdef FAULT_INJECTOR
if (SIMPLE_FAULT_INJECTOR("bump_oid") == FaultInjectorTypeSkip)
{
/*
* CDB: we encounter high oid issues several times, we should
* have some test-utils to verify logic under larger oid.
*/
if (result <= PG_INT32_MAX) {
result = PG_INT32_MAX + result % (PG_UINT32_MAX - PG_INT32_MAX) + 1;
}
}
#endif
return result;
}
/*
* 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
* GetNewOidWithIndex() in catalog/catalog.c. It's also called from
* cdb_sync_oid_to_segments() in cdb/cdboidsync.c to synchronize the
* OID counter on the QD with its QEs.
*/
Oid
GetNewObjectId(void)
{
Oid result;
LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
result = GetNewObjectIdUnderLock();
LWLockRelease(OidGenLock);
return result;
}
/*
* AdvanceObjectId -- advance object id counter for QD and QE nodes
*
* When advancing the Oid counter of a QD, it should only be for the purpose
* of syncing Oid counters logically compared with the numeric maximum Oid
* counter value among the primary segments.
*
* When advancing the Oid counter of a QE, the QD provides the preassigned OID
* to the QE nodes which will be used as the relation's OID. QE nodes do not
* use this OID as the relfilenode value anymore so the OID counter is not
* incremented. This function forcefully increments the QE node's OID counter
* to be about the same as the OID provided by the QD node.
*/
void
AdvanceObjectId(Oid newOid)
{
LWLockAcquire(OidGenLock, LW_EXCLUSIVE);
if (OidFollowsNextOid(newOid))
{
int32 nextOidDifference = (int32)(newOid - ShmemVariableCache->nextOid);
/*
* We directly set the nextOid counter to the given OID instead of
* doing incremental calls to GetNewObjectIdUnderLock(). Update the
* oidCount to VAR_OID_PREFETCH and create an xlog if we have
* exhausted the current oidCount. We should always be moving forward
* and never backwards.
*/
ShmemVariableCache->nextOid = newOid;
if (nextOidDifference >= ShmemVariableCache->oidCount)
{
XLogPutNextOid(ShmemVariableCache->nextOid + VAR_OID_PREFETCH);
ShmemVariableCache->oidCount = VAR_OID_PREFETCH;
}
else
ShmemVariableCache->oidCount -= nextOidDifference;
}
LWLockRelease(OidGenLock);
}
/*
* Requires RelfilenodeGenLock to be held by caller.
*/
static Oid
GetNewSegRelfilenodeUnderLock(void)
{
Oid result;
Assert(LWLockHeldByMe(RelfilenodeGenLock));
if (ShmemVariableCache->nextRelfilenode < ((Oid) FirstNormalObjectId) &&
IsPostmasterEnvironment)
{
/* wraparound in normal environment */
ShmemVariableCache->nextRelfilenode = FirstNormalObjectId;
ShmemVariableCache->relfilenodeCount = 0;
}
if (ShmemVariableCache->relfilenodeCount == 0)
{
XLogPutNextRelfilenode(ShmemVariableCache->nextRelfilenode + VAR_OID_PREFETCH);
ShmemVariableCache->relfilenodeCount = VAR_OID_PREFETCH;
}
result = ShmemVariableCache->nextRelfilenode;
(ShmemVariableCache->nextRelfilenode)++;
(ShmemVariableCache->relfilenodeCount)--;
return result;
}
/*
* GetNewSegRelfilenode -- allocate a new relfilenode value
*
* Similar to GetNewObjectId but for relfilenodes. This function has its own
* separate counter and is used to allocate relfilenode values instead of
* trying to use the newly generated OIDs (QD) or preassigned OIDs (QE) as the
* relfilenode.
*/
Oid
GetNewSegRelfilenode(void)
{
Oid result;
LWLockAcquire(RelfilenodeGenLock, LW_EXCLUSIVE);
result = GetNewSegRelfilenodeUnderLock();
LWLockRelease(RelfilenodeGenLock);
return result;
}
/*
* Is the given Oid logically > ShmemVariableCache->nextOid?
*/
bool
OidFollowsNextOid(Oid id)
{
int32 diff;
diff = (int32) (id - ShmemVariableCache->nextOid);
return (diff > 0);
}
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