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Rework subtransaction commit protocol for hot standby.
This patch eliminates the marking of subtransactions as SUBCOMMITTED in pg_clog during their commit; instead they remain in-progress until main transaction commit. At main transaction commit, the commit protocol is atomic-by-page instead of one transaction at a time. To avoid a race condition with some subtransactions appearing committed before others in the case where they span more than one pg_clog page, we conserve the logic that marks them subcommitted before marking the parent committed. Simon Riggs with minor help from me
This commit is contained in:
Alvaro Herrera
@ -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 1.76 2008/03/26 18:48:59 alvherre Exp $
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* $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.77 2008/10/20 19:18:18 alvherre 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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@ -40,15 +40,12 @@ static const XLogRecPtr InvalidXLogRecPtr = {0, 0};
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/* Local functions */
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static XidStatus TransactionLogFetch(TransactionId transactionId);
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static void TransactionLogUpdate(TransactionId transactionId,
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XidStatus status, XLogRecPtr lsn);
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/* ----------------------------------------------------------------
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* Postgres log access method interface
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*
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* TransactionLogFetch
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* TransactionLogUpdate
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* ----------------------------------------------------------------
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*/
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@ -100,41 +97,6 @@ TransactionLogFetch(TransactionId transactionId)
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return xidstatus;
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}
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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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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, lsn);
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}
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/*
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* TransactionLogMultiUpdate
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*
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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 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, lsn);
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}
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/* ----------------------------------------------------------------
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* Interface functions
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*
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@ -144,11 +106,12 @@ TransactionLogMultiUpdate(int nxids, TransactionId *xids,
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* these functions test the transaction status of
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* a specified transaction id.
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*
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* TransactionIdCommit
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* TransactionIdAbort
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* TransactionIdCommitTree
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* TransactionIdAsyncCommitTree
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* TransactionIdAbortTree
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* ========
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* these functions set the transaction status
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* of the specified xid.
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* these functions set the transaction status of the specified
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* transaction tree.
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*
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* See also TransactionIdIsInProgress, which once was in this module
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* but now lives in procarray.c.
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@ -287,76 +250,22 @@ TransactionIdIsKnownCompleted(TransactionId transactionId)
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return false;
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}
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/*
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* TransactionIdCommit
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* Commits 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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*/
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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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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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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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InvalidXLogRecPtr);
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}
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/*
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* TransactionIdCommitTree
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* Marks all the given transaction ids as committed.
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* Marks the given transaction and children as committed
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*
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* The caller has to be sure that this is used only to mark subcommitted
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* subtransactions as committed, and only *after* marking the toplevel
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* parent as committed. Otherwise there is a race condition against
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* TransactionIdDidCommit.
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* "xid" is a toplevel transaction commit, and the xids array contains its
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* committed subtransactions.
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*
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* This commit operation is not guaranteed to be atomic, but if not, subxids
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* are correctly marked subcommit first.
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*/
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void
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TransactionIdCommitTree(int nxids, TransactionId *xids)
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TransactionIdCommitTree(TransactionId xid, 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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InvalidXLogRecPtr);
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return TransactionIdSetTreeStatus(xid, nxids, xids,
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TRANSACTION_STATUS_COMMITTED,
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InvalidXLogRecPtr);
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}
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/*
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@ -364,29 +273,30 @@ TransactionIdCommitTree(int nxids, TransactionId *xids)
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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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TransactionIdAsyncCommitTree(TransactionId xid, int nxids, TransactionId *xids,
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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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return TransactionIdSetTreeStatus(xid, nxids, xids,
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TRANSACTION_STATUS_COMMITTED, 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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* Marks the given transaction and children as aborted.
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*
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* "xid" is a toplevel transaction commit, and the xids array contains its
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* committed subtransactions.
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*
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* We don't need to worry about the non-atomic behavior, since any onlookers
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* will consider all the xacts as not-yet-committed anyway.
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*/
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void
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TransactionIdAbortTree(int nxids, TransactionId *xids)
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TransactionIdAbortTree(TransactionId xid, 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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InvalidXLogRecPtr);
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TransactionIdSetTreeStatus(xid, nxids, xids,
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TRANSACTION_STATUS_ABORTED, InvalidXLogRecPtr);
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}
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/*
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* TransactionIdPrecedes --- is id1 logically < id2?
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*/
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