Reorder actions in ProcArrayApplyRecoveryInfo()

Since 5a1dfde8334b, 2PC filenames use FullTransactionId.  Thus, it needs to
convert TransactionId to FullTransactionId in StandbyTransactionIdIsPrepared()
using TransamVariables->nextXid.  However, ProcArrayApplyRecoveryInfo()
first releases locks with usage StandbyTransactionIdIsPrepared(), then advances
TransamVariables->nextXid.  This sequence of actions could cause errors.
This commit makes ProcArrayApplyRecoveryInfo() advance
TransamVariables->nextXid before releasing locks.

Reported-by: Thomas Munro, Michael Paquier
Discussion: https://postgr.es/m/CA%2BhUKGLj_ve1_pNAnxwYU9rDcv7GOhsYXJt7jMKSA%3D5-6ss-Cw%40mail.gmail.com
Discussion: https://postgr.es/m/Zadp9f4E1MYvMJqe%40paquier.xyz

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index e2f71da4a016e013694f01bfee98cdcf523913fa..93cdc97166c53c2303ff6a1a4e7000c036b0afc3 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1053,6 +1053,7 @@ void
 ProcArrayApplyRecoveryInfo(RunningTransactions running)
 {
        TransactionId *xids;
+       TransactionId xid;
        int                     nxids;
        int                     i;
 
@@ -1066,6 +1067,16 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
         */
        ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
 
+       /*
+        * Adjust TransamVariables->nextXid before StandbyReleaseOldLocks(),
+        * because we will need it up to date for accessing two-phase transactions
+        * in StandbyReleaseOldLocks().
+        */
+       xid = running->nextXid;
+       TransactionIdRetreat(xid);
+       AdvanceNextFullTransactionIdPastXid(xid);
+       Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
+
        /*
         * Remove stale locks, if any.
         */
@@ -1275,11 +1286,6 @@ ProcArrayApplyRecoveryInfo(RunningTransactions running)
 
        LWLockRelease(ProcArrayLock);
 
-       /* TransamVariables->nextXid must be beyond any observed xid. */
-       AdvanceNextFullTransactionIdPastXid(latestObservedXid);
-
-       Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
-
        KnownAssignedXidsDisplay(DEBUG3);
        if (standbyState == STANDBY_SNAPSHOT_READY)
                elog(DEBUG1, "recovery snapshots are now enabled");