Improve C comments in GetSnapshotData.

Move discussion of why our algorithm for taking snapshots in recovery
to a more appropriate location in the function, and delete incorrect
mention of taking a lock.

diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index fad95ca7ceebac683c7a01a09b98d8f35735ea3c..984c2861cc6b1df350d274fe15c522122c67a690 100644 (file)
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1307,14 +1307,6 @@ GetSnapshotData(Snapshot snapshot)
    /* initialize xmin calculation with xmax */
    globalxmin = xmin = xmax;
 
-   /*
-    * If we're in recovery then snapshot data comes from a different place,
-    * so decide which route we take before grab the lock. It is possible for
-    * recovery to end before we finish taking snapshot, and for newly
-    * assigned transaction ids to be added to the procarray. Xmax cannot
-    * change while we hold ProcArrayLock, so those newly added transaction
-    * ids would be filtered away, so we need not be concerned about them.
-    */
    snapshot->takenDuringRecovery = RecoveryInProgress();
 
    if (!snapshot->takenDuringRecovery)
@@ -1429,6 +1421,12 @@ GetSnapshotData(Snapshot snapshot)
         * Either way we need to change the way XidInMVCCSnapshot() works
         * depending upon when the snapshot was taken, or change normal
         * snapshot processing so it matches.
+        *
+        * Note: It is possible for recovery to end before we finish taking the
+        * snapshot, and for newly assigned transaction ids to be added to the
+        * ProcArray.  xmax cannot change while we hold ProcArrayLock, so those
+        * newly added transaction ids would be filtered away, so we need not
+        * be concerned about them.
         */
        subcount = KnownAssignedXidsGetAndSetXmin(snapshot->subxip, &xmin,
                                                  xmax);