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Add basic infrastructure for 64 bit transaction IDs.

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Instead of inferring epoch progress from xids and checkpoints,
introduce a 64 bit FullTransactionId type and use it to track xid
generation.  This fixes an unlikely bug where the epoch is reported
incorrectly if the range of active xids wraps around more than once
between checkpoints.

The only user-visible effect of this commit is to correct the epoch
used by txid_current() and txid_status(), also visible with
pg_controldata, in those rare circumstances.  It also creates some
basic infrastructure so that later patches can use 64 bit
transaction IDs in more places.

The new type is a struct that we pass by value, as a form of strong
typedef.  This prevents the sort of accidental confusion between
TransactionId and FullTransactionId that would be possible if we
were to use a plain old uint64.

Author: Thomas Munro
Reported-by: Amit Kapila
Reviewed-by: Andres Freund, Tom Lane, Heikki Linnakangas
Discussion: https://postgr.es/m/CAA4eK1%2BMv%2Bmb0HFfWM9Srtc6MVe160WFurXV68iAFMcagRZ0dQ%40mail.gmail.com
This commit is contained in:
Thomas Munro
2019-03-28 10:34:43 +13:00
parent 2a96909a4a
commit 2fc7af5e96
24 changed files with 224 additions and 238 deletions
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34
src/backend/storage/ipc/procarray.c
View File

@ -664,7 +664,6 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
{
TransactionId *xids;
int nxids;
TransactionId nextXid;
int i;
Assert(standbyState >= STANDBY_INITIALIZED);
@ -881,23 +880,10 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
LWLockRelease(ProcArrayLock);
/*
* ShmemVariableCache->nextXid must be beyond any observed xid.
*
* We don't expect anyone else to modify nextXid, hence we don't need to
* hold a lock while examining it. We still acquire the lock to modify
* it, though.
*/
nextXid = latestObservedXid;
TransactionIdAdvance(nextXid);
if (TransactionIdFollows(nextXid, ShmemVariableCache->nextXid))
{
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
ShmemVariableCache->nextXid = nextXid;
LWLockRelease(XidGenLock);
}
/* ShmemVariableCache->nextFullXid must be beyond any observed xid. */
AdvanceNextFullTransactionIdPastXid(latestObservedXid);
Assert(TransactionIdIsValid(ShmemVariableCache->nextXid));
Assert(FullTransactionIdIsValid(ShmemVariableCache->nextFullXid));
KnownAssignedXidsDisplay(trace_recovery(DEBUG3));
if (standbyState == STANDBY_SNAPSHOT_READY)
@ -2001,7 +1987,7 @@ GetRunningTransactionData(void)
latestCompletedXid = ShmemVariableCache->latestCompletedXid;
oldestRunningXid = ShmemVariableCache->nextXid;
oldestRunningXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
/*
* Spin over procArray collecting all xids
@ -2093,7 +2079,7 @@ GetRunningTransactionData(void)
CurrentRunningXacts->xcnt = count - subcount;
CurrentRunningXacts->subxcnt = subcount;
CurrentRunningXacts->subxid_overflow = suboverflowed;
CurrentRunningXacts->nextXid = ShmemVariableCache->nextXid;
CurrentRunningXacts->nextXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
@ -2138,7 +2124,7 @@ GetOldestActiveTransactionId(void)
* have already completed), when we spin over it.
*/
LWLockAcquire(XidGenLock, LW_SHARED);
oldestRunningXid = ShmemVariableCache->nextXid;
oldestRunningXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
LWLockRelease(XidGenLock);
/*
@ -2206,7 +2192,7 @@ GetOldestSafeDecodingTransactionId(bool catalogOnly)
* a safe, albeit pessimal, value.
*/
LWLockAcquire(XidGenLock, LW_SHARED);
oldestSafeXid = ShmemVariableCache->nextXid;
oldestSafeXid = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
/*
* If there's already a slot pegging the xmin horizon, we can start with
@ -3266,12 +3252,10 @@ RecordKnownAssignedTransactionIds(TransactionId xid)
*/
latestObservedXid = xid;
/* ShmemVariableCache->nextXid must be beyond any observed xid */
/* ShmemVariableCache->nextFullXid must be beyond any observed xid */
AdvanceNextFullTransactionIdPastXid(latestObservedXid);
next_expected_xid = latestObservedXid;
TransactionIdAdvance(next_expected_xid);
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
ShmemVariableCache->nextXid = next_expected_xid;
LWLockRelease(XidGenLock);
}
}

2
src/backend/storage/ipc/standby.c
View File

@ -867,7 +867,7 @@ standby_redo(XLogReaderState *record)
* up from a checkpoint and are immediately at our starting point, we
* unconditionally move to STANDBY_INITIALIZED. After this point we
* must do 4 things:
* * move shared nextXid forwards as we see new xids
* * move shared nextFullXid forwards as we see new xids
* * extend the clog and subtrans with each new xid
* * keep track of uncommitted known assigned xids
* * keep track of uncommitted AccessExclusiveLocks