Re: New vacuum option to do only freezing

Hi,

On 2019-04-16 12:01:36 -0400, Tom Lane wrote:
> (BTW, I don't understand why that code will throw "found xmin %u from
> before relfrozenxid %u" if HeapTupleHeaderXminFrozen is true?  Shouldn't
> the whole if-branch at lines 6113ff be skipped if xmin_frozen?)

I *think* that just looks odd, but isn't actively wrong. That's because
TransactionIdIsNormal() won't trigger, as:

#define HeapTupleHeaderGetXmin(tup) \
( \
    HeapTupleHeaderXminFrozen(tup) ? \
        FrozenTransactionId : HeapTupleHeaderGetRawXmin(tup) \
)

which afaict makes
    xmin_frozen = ((xid == FrozenTransactionId) ||
                   HeapTupleHeaderXminFrozen(tuple));
redundant.

Looks like that was introduced relatively recently, in

commit d2599ecfcc74fea9fad1720a70210a740c716730
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:   2018-05-04 15:24:44 -0300

    Don't mark pages all-visible spuriously


@@ -6814,6 +6815,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
 
    /* Process xmin */
    xid = HeapTupleHeaderGetXmin(tuple);
+   xmin_frozen = ((xid == FrozenTransactionId) ||
+                  HeapTupleHeaderXminFrozen(tuple));
    if (TransactionIdIsNormal(xid))
    {
        if (TransactionIdPrecedes(xid, relfrozenxid))
@@ -6832,9 +6835,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
 
            frz->t_infomask |= HEAP_XMIN_FROZEN;
            changed = true;
+           xmin_frozen = true;
        }
-       else
-           totally_frozen = false;
    }

Greetings,

Andres Freund