mirror of
https://github.com/postgres/postgres.git
synced 2025-07-14 08:21:07 +03:00
Support an optional asynchronous commit mode, in which we don't flush WAL
before reporting a transaction committed. Data consistency is still guaranteed (unlike setting fsync = off), but a crash may lose the effects of the last few transactions. Patch by Simon, some editorialization by Tom.
This commit is contained in:
Tom Lane
@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.69 2007/01/05 22:19:23 momjian Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.70 2007/08/01 22:45:07 tgl Exp $
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*
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* NOTES
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* This file contains the high level access-method interface to the
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@ -27,14 +27,17 @@
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static XidStatus TransactionLogFetch(TransactionId transactionId);
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static void TransactionLogUpdate(TransactionId transactionId,
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XidStatus status);
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XidStatus status, XLogRecPtr lsn);
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/* ----------------
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* Single-item cache for results of TransactionLogFetch.
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* ----------------
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/*
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* Single-item cache for results of TransactionLogFetch.
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*/
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static TransactionId cachedFetchXid = InvalidTransactionId;
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static XidStatus cachedFetchXidStatus;
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static XLogRecPtr cachedCommitLSN;
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/* Handy constant for an invalid xlog recptr */
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static const XLogRecPtr InvalidXLogRecPtr = {0, 0};
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/* ----------------------------------------------------------------
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@ -52,6 +55,7 @@ static XidStatus
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TransactionLogFetch(TransactionId transactionId)
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{
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XidStatus xidstatus;
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XLogRecPtr xidlsn;
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/*
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* Before going to the commit log manager, check our single item cache to
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@ -73,9 +77,9 @@ TransactionLogFetch(TransactionId transactionId)
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}
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/*
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* Get the status.
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* Get the transaction status.
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*/
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xidstatus = TransactionIdGetStatus(transactionId);
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xidstatus = TransactionIdGetStatus(transactionId, &xidlsn);
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/*
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* DO NOT cache status for unfinished or sub-committed transactions! We
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@ -84,8 +88,9 @@ TransactionLogFetch(TransactionId transactionId)
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if (xidstatus != TRANSACTION_STATUS_IN_PROGRESS &&
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xidstatus != TRANSACTION_STATUS_SUB_COMMITTED)
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{
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TransactionIdStore(transactionId, &cachedFetchXid);
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cachedFetchXid = transactionId;
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cachedFetchXidStatus = xidstatus;
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cachedCommitLSN = xidlsn;
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}
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return xidstatus;
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@ -93,16 +98,19 @@ TransactionLogFetch(TransactionId transactionId)
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/* --------------------------------
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* TransactionLogUpdate
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*
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* Store the new status of a transaction. The commit record LSN must be
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* passed when recording an async commit; else it should be InvalidXLogRecPtr.
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* --------------------------------
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*/
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static void
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TransactionLogUpdate(TransactionId transactionId, /* trans id to update */
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XidStatus status) /* new trans status */
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static inline void
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TransactionLogUpdate(TransactionId transactionId,
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XidStatus status, XLogRecPtr lsn)
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{
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/*
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* update the commit log
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*/
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TransactionIdSetStatus(transactionId, status);
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TransactionIdSetStatus(transactionId, status, lsn);
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}
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/*
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@ -111,15 +119,16 @@ TransactionLogUpdate(TransactionId transactionId, /* trans id to update */
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* Update multiple transaction identifiers to a given status.
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* Don't depend on this being atomic; it's not.
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*/
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static void
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TransactionLogMultiUpdate(int nxids, TransactionId *xids, XidStatus status)
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static inline void
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TransactionLogMultiUpdate(int nxids, TransactionId *xids,
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XidStatus status, XLogRecPtr lsn)
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{
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int i;
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Assert(nxids != 0);
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for (i = 0; i < nxids; i++)
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TransactionIdSetStatus(xids[i], status);
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TransactionIdSetStatus(xids[i], status, lsn);
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}
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/* ----------------------------------------------------------------
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@ -269,31 +278,49 @@ TransactionIdDidAbort(TransactionId transactionId)
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void
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TransactionIdCommit(TransactionId transactionId)
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{
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED);
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED,
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InvalidXLogRecPtr);
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}
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/*
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* TransactionIdAsyncCommit
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* Same as above, but for async commits. The commit record LSN is needed.
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*/
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void
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TransactionIdAsyncCommit(TransactionId transactionId, XLogRecPtr lsn)
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{
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED, lsn);
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}
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/*
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* TransactionIdAbort
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* Aborts the transaction associated with the identifier.
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*
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* Note:
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* Assumes transaction identifier is valid.
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* No async version of this is needed.
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*/
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void
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TransactionIdAbort(TransactionId transactionId)
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{
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_ABORTED);
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_ABORTED,
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InvalidXLogRecPtr);
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}
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/*
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* TransactionIdSubCommit
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* Marks the subtransaction associated with the identifier as
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* sub-committed.
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*
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* Note:
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* No async version of this is needed.
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*/
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void
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TransactionIdSubCommit(TransactionId transactionId)
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{
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_SUB_COMMITTED);
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TransactionLogUpdate(transactionId, TRANSACTION_STATUS_SUB_COMMITTED,
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InvalidXLogRecPtr);
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}
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/*
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@ -309,9 +336,23 @@ void
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TransactionIdCommitTree(int nxids, TransactionId *xids)
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{
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if (nxids > 0)
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TransactionLogMultiUpdate(nxids, xids, TRANSACTION_STATUS_COMMITTED);
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TransactionLogMultiUpdate(nxids, xids, TRANSACTION_STATUS_COMMITTED,
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InvalidXLogRecPtr);
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}
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/*
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* TransactionIdAsyncCommitTree
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* Same as above, but for async commits. The commit record LSN is needed.
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*/
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void
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TransactionIdAsyncCommitTree(int nxids, TransactionId *xids, XLogRecPtr lsn)
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{
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if (nxids > 0)
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TransactionLogMultiUpdate(nxids, xids, TRANSACTION_STATUS_COMMITTED,
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lsn);
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}
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/*
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* TransactionIdAbortTree
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* Marks all the given transaction ids as aborted.
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@ -323,7 +364,8 @@ void
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TransactionIdAbortTree(int nxids, TransactionId *xids)
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{
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if (nxids > 0)
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TransactionLogMultiUpdate(nxids, xids, TRANSACTION_STATUS_ABORTED);
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TransactionLogMultiUpdate(nxids, xids, TRANSACTION_STATUS_ABORTED,
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InvalidXLogRecPtr);
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}
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/*
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@ -389,3 +431,43 @@ TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2)
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diff = (int32) (id1 - id2);
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return (diff >= 0);
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}
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/*
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* TransactionIdGetCommitLSN
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*
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* This function returns an LSN that is late enough to be able
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* to guarantee that if we flush up to the LSN returned then we
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* will have flushed the transaction's commit record to disk.
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*
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* The result is not necessarily the exact LSN of the transaction's
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* commit record! For example, for long-past transactions (those whose
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* clog pages already migrated to disk), we'll return InvalidXLogRecPtr.
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* Also, because we group transactions on the same clog page to conserve
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* storage, we might return the LSN of a later transaction that falls into
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* the same group.
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*/
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XLogRecPtr
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TransactionIdGetCommitLSN(TransactionId xid)
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{
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XLogRecPtr result;
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/*
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* Currently, all uses of this function are for xids that were just
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* reported to be committed by TransactionLogFetch, so we expect that
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* checking TransactionLogFetch's cache will usually succeed and avoid an
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* extra trip to shared memory.
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*/
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if (TransactionIdEquals(xid, cachedFetchXid))
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return cachedCommitLSN;
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/* Special XIDs are always known committed */
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if (!TransactionIdIsNormal(xid))
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return InvalidXLogRecPtr;
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/*
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* Get the transaction status.
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*/
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(void) TransactionIdGetStatus(xid, &result);
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return result;
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}
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