Remove cut-off bug from RunningTransactionData

32ac7a118fc17f5 tried to fix a Hot Standby issue
reported by Greg Stark, but in doing so caused
a different bug to appear, noted by Andres Freund.

Revoke the core changes from 32ac7a118fc17f5,
leaving in its place a minor change in code
ordering and comments to explain for the future.

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 9db184f8fed09acd1b0c4ccd4e12b4461e07a413..31dddaf0ed5b7a51aa1a74a059f17c811b78a9dd 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1907,7 +1907,7 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
  * GetRunningTransactionData -- returns information about running transactions.
  *
  * Similar to GetSnapshotData but returns more information. We include
- * all PGXACTs with an assigned TransactionId, but not VACUUM processes.
+ * all PGXACTs with an assigned TransactionId, even VACUUM processes.
  *
  * We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
  * releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
@@ -1995,10 +1995,6 @@ GetRunningTransactionData(void)
                volatile PGXACT *pgxact = &allPgXact[pgprocno];
                TransactionId xid;
 
-               /* Ignore procs running LAZY VACUUM */
-               if (pgxact->vacuumFlags & PROC_IN_VACUUM)
-                       continue;
-
                /* Fetch xid just once - see GetNewTransactionId */
                xid = pgxact->xid;
 
@@ -2009,13 +2005,26 @@ GetRunningTransactionData(void)
                if (!TransactionIdIsValid(xid))
                        continue;
 
-               xids[count++] = xid;
-
+               /*
+                * Be careful not to exclude any xids before calculating the values of
+                * oldestRunningXid and suboverflowed, since these are used to clean
+                * up transaction information held on standbys.
+                */
                if (TransactionIdPrecedes(xid, oldestRunningXid))
                        oldestRunningXid = xid;
 
                if (pgxact->overflowed)
                        suboverflowed = true;
+
+               /*
+                * If we wished to exclude xids this would be the right place for it.
+                * Procs with the PROC_IN_VACUUM flag set don't usually assign xids,
+                * but they do during truncation at the end when they get the lock
+                * and truncate, so it is not much of a problem to include them if they
+                * are seen and it is cleaner to include them.
+                */
+
+               xids[count++] = xid;
        }
 
        /*